Chapter 22 Sensors

Variable Reluctance sensor

A Sensor used to measure rotational speed, including wheel speed, engine speed, vehicle speed, and camshaft and crankshaft position.

can potentially cause in-controlled acceleration of an engine.

A Short circuit or incorrect data from the TPS, also called the accelerator position sensor (APS)

Calculating Crankshaft position

A better strategy than using a single sensor on the camshaft is to use both camshaft and crankshaft position sensors. the advantage that two sensors provide is improved precision.

Low Voltage reading

A broken magnet will cause

Voltage Drop

A circuit inside the module monitoring the switch connection will measure the____________ across a fixed resistor inside the ECM

Sending units And Sensors

A distinction is made between

Reference Voltage (Vref)

A precisely regulated voltage supplied by the ECM to sensors; the value is typically 5 VDC, but some manufactures use 8 or 12 volts

Hall Effect Sensor

A sensor commonly used to measure the rotational shaft; they have the advantage of producing signal square waveform and have strong signal strength at low shaft rotational speeds.

Electronic control module

A sensor is considered active or passive depending on whether they use power supplied by the

NOx Sensor

A sensor that detects oxygen IONs originating from nitric oxide from among the other oxygen ions present in the exhaust gas.

Passive Sensor

A sensor that does not use a current supplied by the ECM to operate.

Active sensors

A sensor that uses a current supplied by the ECM to operate.

Piezoresistive Sensor

A sensor that uses piezo resistive crystals arranged with a Wheatstone bridge to measure the change in RESISTANCE of the piezo crystal; these sensors are adapted to measuring vibration and dynamic or continuous pressure changes.

ammonia Sensor

A sensor used in selective catalyst reduction (SCR) that provides data to the ECM that is used to determine if ammonia values are out of anticipated range.

Pull-up Switch

A switch connected between the ECM and a battery positive.

Pull-down switch

A switch connected between the ECM and a negative ground current potential. When the switch is closed, ground current will flow into the ECM.

Thermistor

A temperature-sensitive variable resistor commonly used to measure coolant, oil, fuel, and air temperatures.

Rheostat

A two-wire variable resistor sensor constructed of a fixed input terminal and a variable output terminal, which vary current flow by passing current through a long resistive tightly coiled wire.

Wide-range planar Sensor

A type of sensor technology that uses a current pump to calculate relative concentrations of oxygen, nitric oxide and ammonia in gases.

In Resistive Sensors, the ZVR

Acts as a reference point to measure VOLTAGE DROP across the sensor.

Variable capacitance pressure sensor

An active Sensor that measure both dynamic and static pressures.

Graphing meter

Another important check of hall effect sensors is made using a?

Substrate of Silicon

Another type of piezo resistive sensor uses mineral crystals arranged on a

Resistive Sensors

Are a class of sensors that will condition or change VOLTAGE signal applied to the sensor.

Hall effect TPSs (Non Content Style)

Are even more reliable, because they have no moving parts. This throttle position sensor uses AC magnetic field to induce current in a rotor moved by the throttle pedal. This type of non contact TPS has no sliding parts to wear out.

Dual-path TPS

Are potentiometers.

Potentiometer

Are similar to rheostats in that they vary signal voltage depending on the position of a sliding contact or wiper moving across a resistive material.

Potentiometers

Are three-wire sensors with the SIGNAL WIRE connected to the INTERNAL WIPER. They also supply analog data to processing circuits.

Variable reluctance and galvanic Sensors

Are two examples of voltage generating sensors, this category of sensor is also passive and produces an analog signal of varying voltage or AC frequency.

Switches

At the simplest sensors of all, because they have no resistance in the closed position and infinite resistance in the open position.

HD-OBD System

Because all vehicles are required by emission legislation to monitor engine and other system operations for faults that could produce excessive emissions, evaluating sensor operation is a critical function of the

Functionality Faults

HD-OBD Systems are required to evaluate the operation of at least 12 to 14 other major emission systems =, such as exhaust after treatment boost pressure and EGR

High Bias Resistor

If the arrangement of the pull-up resistor causes signal voltage to go high when disconnected, it is considered

low-bias Sensors

If the tendency for a sensor circuit is to produce a voltage low code when disconnected it is considered?

Crankshaft and cylinder identification

In order to send an electrical signal to fire the injectors, The ECM needs to know two things.

Solenoids

Injectors will use solenoids to meter fuel and adjust timing of injection events.

Transistors

Inside the ECM are most often used to open or close circuits controlling operators.

Mass Air flow sensor

Is a device that measures the weight of air entering the engine intake. Its unique design also reports data about air density and, to some extent, the vapor content.

The third wire

Is a signal return from the sensor. This circuit provides a positive voltage proportional to the physical value measured by the sensor.

Rationality, plausibility, or logical faults

Manufactures use different terms toescribe the same fault detection strategy whereby the validity or accuracy of sensor data is evaluated by comparing sensor voltages with expected values.

Pressure, temperature, and positon sensors are the most common.

Many types of resistive sensors exist, some of these are three-wire active sensors.

12-Volt jumper wire

Never use a what? connected to battery positive to quick check sensor harnesses. The ECM can easily be damaged by this method.

Idle Validation switch (IVS)

One common throttle safety system is the _______________. This circuit uses two switches: at idle, one switch will be open and the other will be closed. off idle the switches change state, which means the normally open switch closes, and the normally closed switch opens.

Reference Voltage

One wire provides reference voltage to the sensor. if it is an active sensor ____________ will supply current to operate an integrated CHIP inside the device.

Voltmeter

Out of range faults on the sensor can be pinpoint tested with a___________by first verifying +Vref and ZVR are available to the sensor.

Field Effect Transistors

Output drivers use (FETs) that are switched either on or off with very small voltages and produce little heat, which makes them ideal for output drivers.

Voltage Generators:

Oxygen sensors, NOx sensors, ammonia sensors, variable reluctance sensors, piezoelectric sensors.

Sensors

Provide information to electronic control units.

The Second Sensor wire

Provides a negative ground signal through the ECM and NOT to the engine ground.

jumper-Wire

Quick testing to determine whether a fault-code is generated by defective wiring, pin connectors, or sensor can be performed using?

ohmmeter

Several temperature and resistance vaues are supplied by the manufacturer to properly evaluate a thermistor when using an?

The Simplest digital Signal is a

Signal pole single throw (SPST) switch. It is found in either an open or closed state.

Calibrated resistor in series with the jumper wire

Some Manufacturers recommend using what? when performing a test to prevent damage to sensitive control modules.

Kirchhoffs Law

States the sum of the voltage drops in a circuit equals source voltage.

High- side Drivers

Switching transistors supplying positive DC voltage are referred to as

Using the Crank Sensor

The ECM can determine exactly where the position of the piston is.

In a positive temperature coefficient (PTC) Thermistor

The Resistance increases as the temperature increases.

Solenoids and relays

The Two basic type of operators are?

Sending Units lack

The capability to Self monitor circuit operation.

NTC

The most common type of thermistor is an ______, In which the sensors resistance goes down as the temperature increases.

In a negative temperature coefficient (NTC) Thermistor

The resistance decreases as the temperature increases.

Variable Resistors

Thermistors are what that change resistance with temperature

Variable Capacitance Sensors And Strain gauge resistive sensors

These are both active sensors that produce analog output signals. Are also a type of pressure Sensor.

Out Of Range Faults

These faults primarily check sensor voltages, and in a few cases they also check current draw.

The Advantage of using three-wire sensors is that

They provide comprehensive diagnostic information about the sensor and its circuit operation.

With a dual track or even three path TPS

To improve reliability of a TPS and validate accelerator position signals, some manufactures are replacing the signal TPS sensor.

Negative and Positive temperature coefficient

Two types of thermistors exist:

Low-side Driver

When supplying a negative polarity or ground to device, current is switched through a transistor called a?

ECM Return or ground is also called

Zero volt Return (ZVR) and is identical to engine ground except it is free of any type of electrical interference.

resistance test

are to test to identify shorted or open wires in harnesses to these sensors.

Silicon-based Piezo resistive sensors

are very sensitive to slight pressure changes.

Worn Gears

can result in a significant amount of gear train backlash, producing unacceptable error in reporting crankshaft postion.

Strain Gauge Wires

construction of this type of pressure sensing device uses resistive wires, embedded in a flexible glass block.

The Advantage of Piezo resistive sensors

is their ability to measure very high pressures. because of there sturdiness of the crystal, piezo sensors are better adapted to measuring vibration and dynamic or continues pressure changes.

A Strain Gauge

measures small changes in the RESISTNACE of tiny wires caused by stretching or contraction.

Knock Sensors

measuring abnormal combustion signals are common application for piezo resistive sensors.

Sending units

provide information to instrument gauges

Resistive Sensors:

rheostats, potentiometers, thermistors, piezoresisitive sensors, And Wheatstone bridge pressure sensors.

PInpoint Test

using break-out harness are performed on live circuits to.

Alternating Current Voltmeter

variable reluctance sensor are two-wire passive sensors. the out put of the sensor can be measured using an.

A Wheatstone bridge electrical circuit

which measures changes in resistance of an unknown variable resistor, is used to measure this small changes in resistance of the strain gauge wires.

The Voltage data

will provide information to processing circuits that will determine whether the circuit or switch is open, closed, out of range, or shorted to ground or positive current potential.