Electrical/Electronics Systems
c4. Differentiate between electrical and engine mechanical problems that cause a slow crank or no crank condition.
First things first: Test the battery. If the battery is good, check all the connections in the starting system. If everything is tight, and corrosion doesn't seem to be a problem, verify the engine will turn over. Turn the crankshaft pulley manually to rule out any internal engine damage. Slow cranking and no cranking can both be caused by issues other than electrical, such as an improperly timed engine. Incorrect timing can cause a slow crank and increased current draw. If you suspect this you can do a compression test, or check the timing marks. Do a voltage drop test on all of the starter components, and a starter current draw test to determine whether or not the starter is causing the slow or no crank problem. (Refer to the steps earlier in the task list for instructions on performing these tests.) An extended cranking problem can many times be caused by fuel or ignition system problems. If the battery voltage and cranking amp readings are within spec, then you may need to start looking at the fuel and ignition systems. Unusual cranking noises are usually caused by mechanical problems related to the starter; such as: loose starter mounting bolts, worn starter drive gear, incorrect clearance between drive gear and flywheel, or worn flywheel teeth. These components should be visually inspected for any abnormal wear, or unusual shaping. Gear marking compound can be used to check the clearance between the starter drive gear and the ring gear. Shims can be used, if necessary, to adjust these clearances.
E1. Diagnose the cause of brighter than normal, intermittent, dim, continuous or no operation of headlights.
A DMM, wiring diagrams, and Ohm's Law will be your best friends when diagnosing problems in these circuits. Possible Causes of brighter than normal lights Bulb problems High Charging system voltage Dimmer switch in high beam position Incorrect setting of automatic dimming sensor Flash to Pass or high beam relay stuck on Possible causes of intermittent operation Bad switches Bad relays Bulb problems Weak circuit breakers Circuit connection issues Headlight relay problems Shorts causing circuit breaker shutdown Possible causes of dim lights Bulb problems Bad grounds Corrosion in relay contacts High resistance in connections Possible causes of Inoperable headlights Bulb problems Shorts causing circuit breaker shutdown Bad relays Bad switches Opens or high resistance in connections Blown circuit breakers or fusible links
a9. Measure and diagnose the cause(s) of abnormal key-off battery drain (parasitic draw); determine needed repairs.
A parasitic draw is when an electrical device stays on and draws current after it should be shut off. Or when a device that normally stays on but draws only a tiny amount of current begins to draw an excessive amount of current. Many systems use power from the battery after the vehicle is shut off: Alarm systems, Clocks, Radios, OBD II evap systems to name a few. Voltage regulators, relays, and light switches are some examples of things that can often times create unwanted parasitic draws. You can test for a parasitic draw using a DMM and a special test switch. Several minutes after the vehicle is shut off, you can connect the meter in series with the battery and tester switch. The average max amp draw is between 35 and 50 milliamps. Consult your ESM for actual specs, and sleep mode times, for accurate tests.
c1. Perform starter current draw test; determine needed repairs.
A specialized ammeter is usually used to perform this test, but there are hand held tools as well, that can give an indication of starter draw. You will connect the meter and crank the vehicle over, and check the amount of current that the starter is pulling to crank the engine. Amperage figures can vary, and they may be published for each particular vehicle. However, an average draw is between 130-200 amps. Some less, some more; it just depends of the engine and the starter. Slow cranking speed, high amperage draw, and low cranking voltage usually indicate a defective starter. Slow cranking speed, low amperage draw, and high cranking voltage usually means there is too much resistance in the starter circuit.
G2. Inspect, test, repair and/or replace components, connectors and wiring of comfort and convenience accessories.
A thorough visual inspection may uncover the problem in one of these complex systems. Connections should be tight, clean, and routed correctly to prevent failure. Use proper repair procedures; solder and heat shrink or crimp-and-seal connectors. A grounding device for the technician is advised when working around sensitive electronic components. You can also touch a metal surface on the vehicle prior to handling a control module to discharge static electricity.
d6. Perform charging circuit voltage drop tests; determine needed repairs.
A volt meter should be connected between the positive battery terminal and the positive terminal of the alternator. If the voltage drop is too high, the resistance is too high and cause an undercharged battery, an over worked alternator. Also do the same voltage drop test on the negative side of the charging system (between the negative battery terminal and alternator case) With the engine running you should see not see more than about .2 volts. Some say .5V is the max drop you want to see, so anything above these voltage drops indicate a problem. Check that the mounting bracket is not damaged, the mounting bolts are tight, and the engine to body grounding strap is in good condition and tight.
a2. Check voltages and voltage drops in electrical/electronic circuits with a voltmeter; interpret readings and determine needed repairs.
A voltage drop test across a component gives a good representation of the condition of that component. Generally, an electrical component should use all of the supplied voltage. If it does not, it is usually safe to say there is a problem with said component.
G1. Diagnose operation of comfort and convenience accessories and related circuits (such as: power window, power seats, pedal height, power locks, truck locks, remote start, moon roof, sun roof, sun shade, remote keyless entry, voice activation, steering wheel controls, back-up camera, park assist, and auto dimming headlamps); determine needed repairs.
Accessories such as power window, seats, locks and trunk locks, sun roofs and moon roofs, and pedal height motors use bi-directional motors. Most of the systems use reversible motors controlled by momentary contact switches. The motors will reverse direction when the polarity is reversed. If power or ground is lost at the main switch, they will fail to operate. If the systems are controlled by a control module, a scan tool will be necessary to help in diagnosis. Voice activated controls, keyless entry, backup camera, park assist, and auto dimming headlight systems are controlled by control modules. These systems use various input sensors that send signals to the logic device to complete the specified action. Scan tools will need to be used to diagnose these systems. In addition, DMMs will be used to test the electronic circuits.
b5. Inspect, clean, and repair or replace battery cables, connectors, clamps and holddowns, vent tubes.
Batteries should be kept clean to prevent surface discharge, and remove corrosion that may be built up. Electrolyte levels should be checked, and added to if low. Maintenance free batteries with hydrometers will have clear or yellow color in the sight glass when the electrolyte level is low, and needs to be replaced. Low electrolyte level can be caused by a system that is overcharging, so keep that in mind when forming a diagnosis. It is recommended to always disconnect the negative cable first. Clean all surfaces, and use some sort of protective coating to prevent corrosion. If there was excessive corrosion on the cables and terminals, you may need to do a voltage drop test on the cables to insure they are fit for re-use. There should be no more than a .5V drop. Secure the battery to prevent it from moving around.
G4. Inspect, test, repair and/or replace components, connectors and wiring of heated and cooled accessories.
If these systems are controlled with a logic device, then a scan tool should be used in diagnostic procedures. You should understand these systems, so you can know which of these systems are in fact controlled by a logic device. Use the same professional wire repair techniques as you would with any other electronic system.
d2. Inspect, adjust, and replace generator (alternator) drive belts, pulleys, and tensioners.
Inspect belt tension with a tension gauge or by measuring belt deflection in the center of the belt span. A belt should have .5" for every 12" of free span. Inspect for wear, glazing, and oil soaking of the belt. Any of these conditions can cause undercharging
E 2. Inspect, test, and repair daytime running light systems.
Many times DRL (daytime running light) systems use the vehicle's high beams as the DRLs. In cases like this, the circuit has a module that reduces the voltage to the high beams to 6 volts, to lower the brightness of the lights. When the headlights are switched on, the module is deactivated, and the lights work normally. When diagnosing these systems, first determine whether the problem is in the DRL or the headlight system. If the problem is in the headlght system, repairs and procedures would be the same as any any system without DRL. If the problem is in the DRL system, and the headlights work normally, only the part that is specific to the DRLs can be the problem.
E8. Inspect, test, and repair or replace switches, relays, bulbs, sockets, connectors, wires, and controllers of courtesy light (dome, map, vanity, cargo, trunk, and hood light)circuits
On late model vehicles, the courtesy lights are typically controlled by the BCM. This is what allows the lights to slowly dim until completely off after the door is shut. Many of these switches are the old one or two wire design, but are wired as inputs to the BCM. BCM controlled switches also allow the switches to turn the lights off after a period of time, to help prevent battery discharge. You may still need to check fuses, wiring and switches in these systems. Door switches may require adjustment as well. If the courtesy lights stay on after the door is shut, an adjustment may be necessary.
G8. Inspect, test, repair and/or replace components, connectors and wiring of entertainment systems.
Please refer to repair procedures listed in earlier sections, as the same type of quality repairs are required.
d1. Diagnose charging system problems that cause an undercharge, a no-charge, or an overcharge condition.
Possible causes of a no charge condition: Bad voltage regulator Bad alternator Loose, corroded, or damaged connections at alternator or battery Bad battery Loose or missing alternator belt Possible causes of an under charging condition: Bad battery Bad alternator Bad voltage regulator Loose, corroded, or damaged connections at alternator or battery Loose or missing alternator belt Possible causes of an over charging condition: Bad battery Bad alternator Bad voltage regulator Loose, corroded, or damaged connections at alternator or battery
b2. Perform battery capacity (load, high-rate discharge) test; determine needed service.
So the preferred method here, again, is an electronic battery tester. Basically what it boils down to is: The battery discharge rate for a capacity test is typically about half of the cold cranking amps (CCA) rating. So the battery will be discharged at that rate for 15 seconds. The battery should at least 75% charged and above 70 F for this test to be accurate. A good battery will remain above 9.6V during the test. The electronic tester does all that for you, and is the preferred method for testing.
a 1. Check electrical circuits with a test light; determine needed repairs.
Test circuits with a volt meter or test light. If the component is getting the required voltage, but non-operative, there is a good chance that component is bad and should be replaced.
b6. Jump start a vehicle with jumper cables and a booster battery or auxiliary power supply.
The recommended procedure is: (booster battery first) Positive then negative; Then on the dead battery; positive then negative. When disconnecting, remove the negative first from the dead battery.
d5. Inspect, and test voltage regulator/field control circuit; determine needed repairs.
The voltage regulator controls the field circuit in the alternator to keep a steady voltage between 13.5 and 14.6 volts. The regulator may be separate from the alternator, but usually in modern vehicles, it is inside the alternator. A faulty regulator can damage the alternator/generator as well. Both should be checked prior to replacing only one. Many late model vehicles have the voltage regulator incorporated into the engine computer. In a case like this, a scan tool can be used to control the charging output with a function test, in addition to retrieving DTCs to help aid in charging system problem diagnosis.
E6. Inspect, test, and repair or replace switches, flasher units, bulbs, sockets, connectors, wires, and controllers of turn signal and hazard light circuits.
Turn signal switches are usually inside the mult-function switch and can be accessed by removing the plastic housing on the steering column. Any repairs made should be done so with solder or crimp-and-seal connectors. Dielectric grease should be used with servicing the bulbs or connectors. Back up light switches are usually mounted around the steering column area, around the shifter, or under the dash. It may be a part of the neutral safety switch. Adjustment of the backup light switch may be possible by loosening the mounting bolts and rotating the switch. Sometimes the ackup light switch is incorporated in the PRNDL switch on the transmission. Some back up lights are controlled by the PCM or TCM and may require a scan tool to diagnose.
E4. Inspect, test, and repair or replace headlight and dimmer switches, relays, control units, sensors, sockets, connectors, and wires of headlight circuits.
Typical headlight systems include the following components: headlight switch, high beam switch, relays, fuse, connector, wiring, sockets, and bulbs. You should visually inspect the circuit components for obvious damage, and then proceed to voltage testing. On newer systems controlled by logic devices such as body control modules, or lighting control modules, use a scan tool to help in diagnosis. The scan tool can retrieve DTCs and can be used to command the elctrical items. Keep in mind that if the correct voltage is supplied to the bulb, and dropped, the problem must be in the bulb or the socket. If there is no voltage to the bulb, then follow the circuit to previous component. Always use wether resistant connections when making repairs.
E7. Diagnose the cause of intermittent, dim, continuous or no operation of courtesy lights (dome, map, vanity, cargo, trunk, and hood light).
When diagnosing interior lighting problems, you will be dealing with 2 types of systems. The conventional systems where lights are controlled by switches that directly control power or ground. You will use a volt meter to diagnose these systems. Another system utilizes the BCM to control these lights. The switches can be "normally open" or "normally closed" and may be resistive switches that vary their resistance as they operate. A scan tool would be necessary to diagnose problems with these systems. A scan tool can display the output of the resistive switches to help you determine the functionality of the switches.
a6. Use scan-tool data to diagnose electronic systems; interpret readings and determine needed repairs.
You will need a scan tool on many diagnostic procedures with late model vehicles. So basically they allow you to do many things, including: 1. View live data of different systems on the vehicle 2. Retrieve DTCs 3. Energize circuits to test functionality 4. Test circuits 5. Providing possible problems within certain systems Scan tools are invaluable. When viewing data reported by the scan tool from a certain system, compare it to known good data provided your service manual or an ESM. Using this data will help you determine which diagnostic or repair route to take.
a8. Find shorts, grounds, opens, and resistance problems in electrical/electronic circuits; determine needed repairs.
ok sorry let's do the definition thing again, just in case.. Short Circuit: Is a change is the intended electrical path. A volt meter would be used to test shorts typically. Grounded Circuit: A short to ground; when the electrical path goes to ground within the circuit before it is intended to. A short to ground on the power side of the circuit can cause serious problems. The current will be sent in a short loop, bypassing the load. The massively decreased resistance will cause current flow to multiply. If the circuit is protected, usually a fuse will blow, or circuit breaker trip. A short to ground on the ground side will usually not affect the circuit. An exception would be if the circuit is switched on the ground side (a horn for example). A short to ground in this case would cause the component to operate continuously. An ohmmeter is the preferred tool for testing grounded circuits. Ohmmeters will energize the circuit, so power must be disconnected from the circuit prior to testing. Open Circuit: One that has no continuity, or does not allow current to flow. This is my favorite. Why? Because of the different factors involved in testing. A Voltmeter, ohmmeter, or continuity test can be used to test these circuits. High Resistance Circuit: A circuit that has reduced current flow due to corrosion, loose terminals, burnt contacts, partial opens, etc. Reduced current flow is directly proportional to the amount of resistance present. (Remember Ohm's Law) The higher the resistance the lower the the amount of current that can flow. Resistance is measured with on ohmmeter. The ohmmeter will energize the circuit so it is important that the original source be disconnected. You can can also test these type of circuits with a volt meter. To do that, the original power source would need to be connected and ON. You would connect the meter in parallel with circuit and measure the "voltage drop" between the power source and the positive side of the load. For example: Source voltage (battery voltage) is 12.6 V, but between the starter motor and the battery you measure of voltage drop (difference; variance) of 3 volts. You can conclude that there is enough resistance in the cable you are losing 3 volts. Anything more than roughly .3 volts is considered an unacceptable voltage drop for a wire. Find the place with the highest resistance and correct the problem, whether it be terminals, wires, or connectors or all of the above. In any case, use your digital multimeter in conjunction with jumper wires we talked about above to isolate problem areas. Once you have isolated and confirmed the problem, replace the necessary component.
G9. Diagnose operation of safety systems and related circuits (such as: airbags, seat belt pretensioners, occupancy classification, wipers, washers, speed control/collision avoidance, heads-up display, park assist, and back up camera); determine needed repairs.
Airbag warning lights are typically designed to stay illuminated a few seconds after the engine is started, while it performs its checks. If everything checks out, the light will go out. If the light does not go out, there is a fault in the airbag system. When the airbag is set to diagnostic mode, the light will flash codes. If this light fails, there may also be a backup that utilize a tone, through the waning chime system. A diagnostic tool can be used to retrieve airbag fault codes. Air bag systems may be "aware" of the number and size of the occupants in the front seats. The passenger seat may have a pressure sensor that detects the weights of the passenger, and if the occupant weighs less than a given amount, the airbag may not deploy at the same level, or may not deploy at all. If the sensor detects no weight in the seat, the passenger airbag may not be deployed at all in the event of a collision. These sensors require calibration and diagnosis by using a scan tool. Some wiper motor will contain a series field coil, shunt field coil, and a relay. When activated the relay winding is grounded through one set of switch contacts. This closes the relay contacts, supplying current to series field coil and armature. The wiper motor would then start turning. If the wiper switch is in the high speed position, the shunt coil would not be grounded, and motor would turn at a high speed. When the wiper switch is set to low speed, the shunt coil is grounded through a second set of contacts. Current would flow through the shunt coil and the wiper switch to ground. A strong magnetic field that induces more opposing voltage in the armature windings, occurs when current flows through the shunt coil. This opposing voltage in the windings will reduce current flow through the series coil and windings, and slow the armature. If the wiper motor will not park, or parks in the wrong position, the parking switch or cam is likely faulty. A wiper motor may have permanent magnets instead of field coils. These motors will have a low and high speed brush. The low speed brush may be directly opposite the high speed brush, and the high speed brush would be in between the two. Constant operation of wipers could be caused by a short in the control circuit, or defective or stuck switch. Wipers that fail to park may have a defective park mechanism inside the motor, damaged park circuit, or damaged intermittent wiper unit. Intermittent wipers may be caused by a loose or damaged wire or connector. Inoperable wipers can be caused by a bad wiper motor, or an open somewhere in the circuit. The washer system is fairly simple and consists of a pump mounted inside the washer reservoir, that when supplied voltage will pump washer fluid through the hoses, and to the sprayers. The washer pump may be controlled by the BCM, so when the switch is activated the BCM will activate the wipers for a few cycles. When diagnosing the washer system, check for bad connections and washer fluid levels. Disconnect the hose at the pump to verify whether or not fluid will stream out when the switch is activated. If it does, check for broken or clogged washer hoses, or nozzles. Verify the pump receives voltage to determine whether there is an open in the circuit caused by a bad switch or damaged wire, or connection. Cruise control systems may combine electrical components, mechanical linkages, and vacuum operated components. Check for binding in the linkage before testing vacuum and electrical components. Adjustment of the linkage may be necessary. Vacuum devices can be checked with a hand held vacuum pump. The diaphragm should move when vacuum is applied. The unit should be able to hold vacuum, and the diaphragm should release when vacuum is released. In some systems the control module and steeper motor may be combined in one unit. The stepper motor is connected to the throttle linkage by a cable. The cruise control switch, brake switch, and VSS (vehicle speed sensor) provide inputs to the control unit. The stepper motor receives commands from the control module to determine the desired throttle opening. A defective VSS can affect cruise control operation. Some vehicles may actuate an electric servo motor with a cable attached to the throttle body or linkage to control speed, controlled by the PCM. VSS, brake switch, steering wheel, and cruise switch inputs will send information to the PCM which will control the speed, and monitor the speed via the VSS. These signals can be transferred through the clock spring, so a damaged clock spring can affect any of the systems that run through it. Some cruise control systems have the ability to slow the vehicle an object or vehicle is quickly approaching. This system uses radar to sense these objects. Inspection of the transmitter and receivers should be preformed when diagnosing cruise problems. HUD or heads up display systems project instrument panel data onto the windshield. The HUD uses mirror technology to perform the projection. Normal instrument panel diagnostic procedures can be used when working on this system. Park assist systems typically use sensors mounted in the rear bumper to detect objects within close proximity when backing up. Close object will trigger indicators inside the vehicle to warn the driver. These systems have diagnostics integrated into their software and should be tested with a scan tool. Back up cameras are usually mounted in the rear bumper and will display on a screen inside the vehicle when it is in reverse. Faults can happen in the camera, the screen, or the wire harness. Inspect for physical damage, connection condition and tightness, etc. A scan tool can be used to communicate with this system.
a11. Read and interpret electrical schematic diagrams and symbols.
Alright so this is task item that i can't help with too much. I don't really have the hardware to make these images or scan them in. So just Google "automotive electrical symbols" or something like that. You will find many pictures of them. You WILL need to be familiar with them, AND how to efficiently read a wiring diagram. Your ASE test will ask you more than a couple questions involving a wiring diagram. Get to know these diagrams. And VERY IMPORTANT!!! Pay attention to what side the ground is on a given component in the wiring diagram. It can be confusing if you dont read the question and the diagram carefully. The following 2 statements helped me a lot and I will pass them on: 1. You can't really short to ground if it's on the ground side. 2. An open can't really be the problem, if the circuit is normally open anyway - Not when the device stays on continuously But for these things to help you, YOU MUST BE ABLE TO EFFECTIVELY READ A WIRING DIAGRAM. sorry no more preaching Diagnose failures in the data bus communications networks; determine needed repairs. The data bus communications network is basically the network that allows the vehicles computers to communicate with each other, as well as scan tool communication. Usually the network consists of two wires connected various modules and the DLC in parallel. The process of pulsing voltage to send signals is call bussing or multiplexing. Most vehicles now days will have multiple data networks. The fastest is CAN (Controller Area Network). These networks may have terminating resistors at each end to help reduce interference on the network. These resistors should be tested while the ignition is off. Use your ohmmeter to measure the resistance between pins 6 and 14 of the DLC. The reading should be 60 ohms. Common problems in these systems will be shorts, opens, and resistance where there shouldn't be. To test these networks, you will use a DMM, DVOM, etc and a diagnostic trouble chart. Oscilloscopes can be used as well to motor high speed voltage activity. This activity would indicate some sort of communication is happening. Scan tools can be used but only if it can communicate with the systems. Check the DLC and scan tool leads as they can be potential trouble areas. Remove and replace control modules; program as needed. So the electronic control modules (ECMs) communicate with the computer and each other via the data bus networks or CAN. You should verify that all the electrical components are in good working order; Eg. starting and charging system, connectors, powers and grounds, etc. Disconnecting the neg battery cable, and wearing a grounding strap are not a bad idea. You really don't want to have any static built up on you when working around sensitive computer components. Make sure all connections are tight and any sort of hold down for the control module is re-installed, to prevent the module from moving around. Many modules need to be programmed. A scan tool or programming tool with the correct software will need to be used to program the module. After programming use a scan tool to operate the system to verify correct operation.
d8. Remove, inspect, and replace generator (alternator).
Always disconnect the battery terminal prior to removing the alternator. Verify the alternator case, mounting holes, and pulley size are the same as the original. Take care not to over tighten any connection at the alternator. A small amount of torque is all it takes.
a3. Check current flow in electrical/electronic circuits and components with an ammeter; interpret readings and determine needed repairs.
Ammeters are connected in series with electrical circuits. Higher than normal currecnt flow would indicate high voltage or low resistance. Low current flow would indicate too high resistance or too low voltage.
a5. Check electronic circuit waveforms using an oscilloscope; interpret readings and determine needed repairs.
An oscilloscope converts electrical signals to a visual representation of voltage signals over a period of time. An upward wave means a voltage increase. A downward wave means a voltage derease. A FLAT line indicates steady voltage. Compare your findings to what the changes in voltage should be to make a determination on whether or not the component is functioning properly.
G5. Diagnose operation of security/anti-theft systems and related circuits (such as: theft deterrent, door locks, remote keyless entry, remote start, and starter/fuel disable); determine needed repairs.
Anti-theft systems use a control module. This may be a dedicated module, or integrated into an existing one. Most factory installed systems are passive, meaning they are designed to start the system when the correct key is inserted. The system may disable the ignition, fuel system, starter system etc if the correct key is not inserted. Active anti-theft systems are designed to arm when the system is activated or a series of events occurs that automatically arm the system. An active system may sound the vehicle's horn and disable the starter if an attempt to break in to one of its coverage zones occurs. These zones can include trunk, doors, hood, ignition, radio, etc. Some convertibles may have active ultrasonic sound waves that protect the interior. False alarms can be caused by overly sensitive sensors, or misplaced sensors. Some shock and glass sensors may have 2-stage mechanisms that give warning when the first threshold is reached, and sound the alarm when the second threshold is reached. Door sensor may send false signals if they become rusty, or if moving parts begin to wear out. The dome light circuit may be tied into the alarm system as well, to signal that a door has been opened. They may be tied into the door ajar switch, or have their own dedicated switch. Separate switches may be used if the vehicle has door handle switches that signal to a control module that the door is open. Remote keyless entry is tied to the power door lock system. The transmitter send signals the the control module that will send voltage to the relay winding and perform the desired function. Typically the interior lights will illuminate when the unlock button is pressed. The keyless entry module will turn off the lights after a certain period of time, or when the ignition is turned on. Remote start systems will use the same technology as the remote door locks, and theft deterrent systems. When activated, the BCM will send signals to the necessary devices to start the engine. The doors will remain locked until the driver nears the vehicle and activates the unlock function.
G7. Diagnose operation of entertainment and related circuits (such as: radio, DVD, remote CD changer, navigation, amplifiers, speakers, antennas, and voice activated accessories); determine needed repairs.
Audio systems, typically, will either work, not work, or be noisy. The faulty component should be isolated and replaced. Check that there is the proper voltage to the unit, and if there is, the entire unit may need to be replaced. Sound quality may be affected by loose speakers, speaker grills, or trim panels. Check the tightness of all these things when diagnosing a rattle or buzz. Sound distortion can be caused by defective speaker, radio chassis, or wiring. If the problem is the radio chassis, all speakers on the same side of the vehicle will exhibit the distortion. Damaged wiring can cause sound distortion, and low output of sound. Static can be caused by ignition or charging systems. Bad engine grounds, or sound system grounds can cause static. Different systems may have suppression devices such as a suppression coil on an instrument voltage limiter, or a clamping diode on an electro-magnetic clutch. If defective, these suppression devices can cause static in the sound system. Damaged or missing ground shielding on an antenna may cause static as well. Voice activation systems allow the driver to perform many functions without pushing a button. The technology used may be adaptive to driver's speaking style and voice patterns. Systems that may be controlled by voice can include audio systems, climate control, mobile phone, navigation. The voice activation systems are integrated into existing body electronic functions, and will require a scan tool during diagnostics.
G10. Inspect, test, repair and/or replace components, connectors and wiring of safety systems.
Before servicing the airbag system, disconnect the battery, and allow the specified amount of time for the vehicle to completely power down. Never use a powered test light, or ohmmeter to diagnose an airbag system. Use a volt meter or the manufacturer specified diagnostic tool only. Wear appropriate protective equipment when servicing airbag systems. Airbag sensor MUST ALWAYS be mounted in their original position facing the direction that its airbag is on. The sensors may have arrows on them indicating the directions they should face. Always carry inflatable devices away from your body and walk slowly and carefully, to avoid tripping. Carry them with the trim piece pointing away from your body, and store modules face up only. Refer to the service manual for the procedure in disarming an airbag. The procedure generally involves removing the negative battery cable and taping it it to prevent accidental connection. The airbag fuse would then be removed, and wait a period of time (about 10 minutes) to allow any stored energy to dissipate, before servicing the airbag system. This a generic procedure, so always refer to the manual for the exact procedure. admin - ASE Certified Technician
c2. Perform starter circuit voltage drop tests; determine needed repairs.
Disable the ignition and fuel system before performing these tests. Check the voltage drop between each component in the starter circuit while operating the starter motor. Voltage drop between each component should not exceed .5V. The entire circuit should not exceed 1.5V. Anything more would be considered excessive. If you placed one lead from your voltmeter at the POS BAT terminal and the other lead to the POS terminal at the starter solenoid, then cranked the motor, you would not want to see more than a .5V drop.
G6. Inspect, test, repair and/or replace components, connectors and wiring of security/anti-theft systems.
Due to the placement of components in these systems, visual inspection of its components can be difficult. Wiring diagrams and parts locator guides can be used to aid in diagnosis. These circuits can be treated like most other circuits when diagnosing. Opens will prevent operation of affected component(s). Shorts can blow fuses, or circuit breakers. Unwanted resistance will cause the system to function properly. There may be many sensors and controllers in these systems, so a scan tool is a must when diagnosing them.
F5. Inspect, test, repair and/or replace bulbs, sockets, connectors, switches, relays, sensors, timers, wires, gauges, sending units, sensors, electronic components, and controllers of electronic instrument clusters and driver information system circuits.
Electronic gauges can either be analog or digital. Digital circuits will operate in one of two ways: On or Off. The pulsing of the circuit determines the readings on the guage. Analog gauges give the ability to show a constant change in values. In order for an electronic gauge to show an accurate reading, it must receive an accurate signal from its sensors. Check the connections and wiring at the sending unit. If the sending unit is unplugged, the gauge should respond. A typical gauge circuit is a simple series circuit with a variable resistor. A change in circuit resistance will cause a change in current flow and affect the reading on the gauge. Unwanted resistance from corrosion or whatnot, as well as high voltage from defective sending units, will cause incorrect gauge readings. Sending units are tested with an ohmmeter, comparing your findings to the published values the sending should have in various conditions. You may also need to do a voltage check at the gauge to help determine the problem. Sending units, controllers, gauges, and circuit boards are not repaired, but replaced, if found to be defective. Driver information systems are integrated with the communications network and display data on a screen on the dash. A scan tool will be needed to diagnose problems with this system. The display can be replaced as an entire unit, if it is found to be defective.
E9. Inspect, test and repair or replace trailer wiring harness, relays, connectors, and controllers.
Factory trailer wiring harnesses may have wiring diagrams available to aid in diagnosis. Plug and play wiring harnesses may be used as well. And in some cases, you may run across splicing and un-conventional wiring methods for trailer wiring harnesses. In any case, a voltmeter will be used to diagnose problems. You should have source voltage available for running lights, brake, and turn signals. Isolate the problem circuit, and make the necessary repairs.
E3. Inspect, replace, and aim headlights/bulbs, and auxiliary lights (fog lights/driving lights).
Halogen and xenon bulbs should always be allowed to cool before removal. New bulbs should only be handled by the plastic base to prevent premature failure. The glass needs to be free of any contaminants including: grease, moisture, dirt etc. The bulb contacts should be coated with dielectric grease to minimize corrosion. Replacement HID lamps may be brighter than originals, due to their age. It might be a good idea to let the customer know this, and give them the option of replacing both of them. Aiming headlights can be done using alignments tools, or built on built aiming mechanisms or aiming bubbles. Face the vehicle towards a wall, maybe 10 feet away. Turn on the headlights, and use the correct tool or procedure to adjust the level of the light beams. Use a wiring diagram, if available, to diagnose auxiliary lighting systems. They can be tricky as some may only operate when the low beam lights are on, or only when the key is, are only when the headlights are off. It is important to refer to the wiring diagram, so you can know what situation you are dealing with.
G3. Diagnose operation of heated and cooled accessories and related circuits (such as: heated/cooled seats, heated steering wheel, heated mirror, heated glass, and heated/cooled cup holders); determine needed repairs.
Heated systems generally use thermo-electric strips to create heat when power is supplied to them. The large amount of current drawn from these systems require them to use a relay. A control module will direct the relay when the person activates the switch. The systems are fairly simple and can be diagnosed using the same techniques as used in other circuit types. Cooled seats utilize perforated seats that direct air from the AC system through the seat. The seat may even have its own blower motor to aid in air movement through the seat cover. The seats should be cleaned and maintained to help prevent blockage of the perforations. The blower motor in the seat can be tested using a scan tool. Heated and cooled cup holders use electric grids that add or remove heat depending on the polarity of the current supplied. A switch controls the polarity based on the desired temperature by the driver or passenger. Heated steering wheels have a built in heater grid. The current path for this system is delivered through the clock spring/ribbon. A scan tool can be used to diagnose problems with this system.
a7. Check electrical/electronic circuits with jumper wires; determine needed repairs.
I am not sure if this still in the task list but I will include it anyway. So basically the purpose of this is to supply direct battery voltage to a certain electrical component and see if it works. Straight forward right? Many call this "jumping" or "hot-wiring" the component. You will need to use this technique often, especially on older vehicles. For example: if you are not sure whether or not an AC compressor is bad. Ok, so you have verified the freon charge in the system is correct, the fuse is good, the relay is good, but the compressor clutch still won't operate. So why not "jump" it? Send a jumper directly to the compressor clutch power wire and see if it turns on. If it does, then you can move on to your next test. If not, then there is something wrong in the compressor or clutch. This procedure can be used when testing a number of components. Eg. power window motors, blower motors, radiator and condenser fans, door lock actuators, power release mechanisms, and more. (Keep in mind that the component being tested should be unplugged from its original power source when performing the test)
c3. Inspect, test, and repair or replace switches, connectors, and wires of starter control circuits.
If a relay or switch is open, and you connect your ohmmeter across the contacts, you should see OL or infinite reading. This indicates the switch is open. If it is supposed to be open, then that test is complete. If it shows a low resistance, meaning it is closed, but it should be open, you will know the switch is faulty. When measuring resistance in a relay winding, there should be a resistance value. Compare it to the specified resistance. If it's too low there is a short in the winding. If too high, there is an open. A starter solenoid is basically a relay, and can be tested similarly, with your ohmmeter Test leads across the "S" terminal and the "motor" terminal will test the pull-in winding. Test leads across the "S" terminal and the ground will test the hold-in winding. A voltage drop across the load side of the high current contact, while in operation, i method of testing for burnt contacts. When replacing starter, verify shims are installed if needed. Bench test new starter. Check all contacts and connections for cleanliness and tightness. Check wires for corrosion, and replace if voltage drop is excessive.
b1. Perform battery state-of-charge test; determine needed service.
In the shop you will be using an electronic battery tester typically, but it may be more involved on the test. In flooded, non-maintenance free batteries, a hydrometer can be used to perform this test. Each cell should be 1.265 specific gravity points. That would be considered a fully charged battery. For every 10 degrees above 80F you would add .004 specific gravity points to your readings. For every 10 degrees below 80F, you would subtract .004 specific gravity points. (It is the temperature of the electrolyte in the battery, not the ambient temperature). So you measure each cell, and make your adjustments for temperature for each cell. Each cell should exceed 1.265 specific gravity points on a fully charged battery. .050 specific gravity points is considered the maximum allowed variation between cells. When referring to voltage: 12.6 V = 100% 12.4 V = 75% 12.2 V = 50% 12 V = 25%
E5. Diagnose the cause of turn signal and/or hazard light system malfunctions; determine needed repairs.
Most turn signal flashers are load sensitive and will change the speed they flash when the electrical current changes. This notifies the driver in case a bulb burns out. A hazard flasher is normally a heavy duty flasher. Heavy duty flashers can be installed in the place of non heavy duty flasher when connecting to a trailer wiring harness. It is not uncommon for the turn signal to flash at a different rate when connected to the trailer harness. A heavy duty flasher will help eliminate this condition. Common problems with these systems include: faulty flasher, bad bulbs, incorrect bulbs, bad grounds, resistance in circuit from corrosion, and shorts. Brake light switches can be involved too, if the turn signals share a bulb with the brake lights.
b4. Perform slow/fast battery charge in accordance with manufacturer's recommendations.
Never attempt to fast charge a cold battery. Use common sense. Batteries should not exceed 125F when charging because this can damage them. Slow charging is usually the best way to go, but as long as you following safe charging procedures, there shouldn't be any issues.
F1. Diagnose the cause of intermittent, dim, no lights, continuous operation or no brightness control of instrument lighting circuits.
Possible causes of dim Bad grounds High resistance in connections Bulb problems Corrosion Possible causes of No lights Bulb problems Bad relays Blown circuit breakers or fusible links opens or high resistance in connections High beam switch in the on position or faulty (driving/fog lights) Bad switches Shorts causing circuit breaker shutdown Possible causes of Intermittent Operation Faulty relays Connection issues Shorts causing circuit breaker shutdown Bulb problems Possible causes of brighter than normal High charging system voltage Bulb problems It is important to keep in mind whether the problem you are diagnosing is affecting one bulb or multiple bulbs. If only one bulb is affected, you should concentrate on system components that could affect just that bulb. If the problem affects all bulbs on the circuit, you should be looking for things that are common to all the bulbs.
F3. Diagnose the cause of high, low, intermittent, or no readings on electronic instrument cluster gauges; determine needed repairs.
Refer to previous sections to see possible causes of the conditions. In addition, remember that the instrument panel lighting can be controlled by a rheostat. In this case the instrument panel dimmer switch. A problem with this switch would affect all bulbs in the circuit. A problem with one bulb would cause all bulbs to not work, as they are wired in parallel to the battery.
F2. Inspect, test, and repair or replace switches, relays, bulbs, LEDs, sockets, connectors, wires, and controllers of instrument lighting circuits.
Regardless of the light circuit being diagnosed, it is always a good idea to visually inspect the circuit for loose connections, damaged wires, and corrosion. Typically in a circuit with multiple bulbs, if only one is not working, it is safe to assume the bulb is burned out, or there is a problem in that bulb's socket. In this case you could replace the bulb, and visually check the condition of the socket. If more than one bulb is not working, then typically the bulb is not the issue. Check for opens in the circuit and opens in the bulb. An open bulb can be verified with an ohmmeter. An open would read infinite resistance or OL. Some electronic instrument panels use logic devices to control the lighting operation. You would use a scan to retrieve DTCs from the instrument panel.
d3. Perform charging system output test; determine needed repairs.
The easiest way to perform a voltage output test is by connecting a volt meter to the battery while the engine is running. The battery should be at least at 75% charge before performing this test. You should see between 13.5 and 14.6 volts across the battery terminals. Anything higher or lower than this, you should address the condition of the alternator, or voltage regulator.
a10. Inspect, test, and replace fusible links, circuit breakers, fuses, diodes, and other current limiting devices.
This should be the most straight forward section. Use your best friends: Your your DMM, DVOM, or multimeter or whatever you want to call it, and a test light or probe. You will be measuring resistance and voltage (or absence of voltage) for the most part. The simplest way to explain this is - Where you know you should have voltage, test for voltage. If there is none, check the resistance. If your ohmmeter say OL (Out of Limits), then you have a problem. Fuses, link, circuit breakers you can pretty much test the same way. Test for voltage on either side of the fuse. If you have voltage on one side but not the other, the fuse is bad. If you have voltage on both sides, it's good. If there is no voltage to the fuse, then you need to follow the wire backwards to the next component and repeat the test until you find your faulty component.
d4. Perform generator (alternator) output test; determine needed repairs.
This test can be performed with a device known as a carbon pile. You will need to know what the alternator output is supposed to be if working normally. The device will apply a load to the alternator (all the vehicle accessories should be off). If the alternator cannot supply the specified output, there is a problem. You will need to determine whether it is an internal problem with the alternator or regulator, or simply a problem in the circuit's wiring.
F4. Diagnose the cause of constant, intermittent, or no operation of warning lights, indicator lights, audible warning devices, and other driver information systems; determine needed repairs.
Typical causes constant operation of warning lights are: control circuits shorted to ground, or switch or sender shorted out. An intermittent light could be caused by a loose wire or connector. A no operation condition could be a burned out bulb or an open in the circuit. Many of these lights are controlled by the BCM. The BCM will use signals from the various switches and senders, and ground the appropriate circuit to illuminate the light. Service on these systems is the same as in other light systems. Use solder and heat shrink or crimp-and-seal connectors. The BCM may use inputs from several switches and senders to illuminate warning lights. They may use a combination of the ignition switch, seat belts, door switches, wiper switch, horn, anti-theft inputs, vehicle speed inputs, brake light switch, head light switch, etc to illuminate warning lights, and sound chimes or buzzers. A scan tool is the best way to help pin-point the problem area. Testing beyond this would be the same as testing any other switch. You would use on ohmmeter or voltmeter. Tone generators should be tested by running them through the prescribed self-test mode. They are usually activated by the closing of a switch. The PCM or BCM generally triggers these systems. Use the manufacturer recommended procedure for testing them.
a4. Check continuity and resistances in electrical/electronic circuits and components with an ohmmeter; interpret readings and determine needed repairs.
When measuring continuity, make sure the circuit is not energized. The meter will supply its own power to perform this test, and meter damage can occur if the circuit is energized. Use the continuity test to find opens in circuits, where there should not be opens. No continuity would indicate an open. Continuity would indicate the circuit is closed. If it supposed to be closed, but there is no continuity, then you can assume there is a problem. On the other hand, if the circuit is supposed to be open, but there is continuity, there is a problem. Resistance specs are published on most everything these days. Use an ohmeter to measure resistance of the component in question, and compare to published specifications. If not within range, there is a problem.
d7. Inspect, repair, or replace connectors and wires of charging circuits.
When repairing electrical circuits, always use rosin core solder, insulate bare wires with heat shrink tubing, and if the wire contains a shield wire, solder the drain wire separately.
b3. Maintain or restore electronic memory functions.
When the battery is disconnected on newer vehicles, all kinds of things get erased. Not just the radio presets and clock, although the customer will be the most upset about this). But memory seats, mirrors, steering wheel placement, etc. In addition to that, all the data in the PCM will be gone, and can cause less than desirable vehicle behavior afterwards. After about 20 miles of driving, the computer will relearn and will return to normal operation. A 12 V power supply can be connected to the auxiliary power outlet to save computer memory. Some technicians will use another battery connected to ground and the main power fuse. Either way will work the same.
