engine pref CH6
Technician A says that the air-fuel ratio sensor produces below 3.3 volts in a negative direction when the exhaust is rich. Technician B says that the air-fuel ratio sensor operates at a lower temperature than the conventional oxygen sensor.
A
While discussing O2 sensor diagnostics, Technician A says that the speed of switching from rich to lean is important. Technician B says that the voltage levels attained (toggling from high to low) are also important.
A
While discussing the term fail soft, Technician A says that a fail-soft problem exists when a sensor fails and the ECM is able to substitute a value for the sensor and the vehicle is able to be driven until it can be repaired. Technician B says that a fail soft is a failure of the system software.
A
While discussing vehicle speed sensors (VSS), Technician A says that the resistance of the VSS coil can be checked with an ohmmeter. Technician B says that the VSS produces a DC voltage signal that is sent to the PCM.
A
The signal from most sensors must be amplified and converted from:
A- Analog to digital
Technician A says that the Hall-effect switch contains an electromagnet. Technician B says that the Hall-effect switch also uses a shutter wheel connected to a rotational component.
B
Technician A says that the engine coolant temperature (ECT) sensor signal is used by the PCM to provide a lean mixture when the engine is cold. Technician B says that the signal is used by the PCM to provide less spark advance on a hot engine.
B
A noncontact-style TP sensor is used on some vehicles. Technician A says that electrically, the output of the sensor looks much like the action of two potentiometers. Technician B says that the linear Hall-effect TP sensor has the advantage of no contacts to wear or contaminate.
C
EMI is being discussed. Technician A says that EMI can cause drivability problems. Technician B says that EMI is worse with poor grounds.
C
Technician A says that an analog signal is variable within a given voltage range. Technician B says that a digital signal is either on or off.
C
Technician A says that computer feedback is information sent back to the computer to confirm that a command was carried out by an actuator. Technician B says that feedback can also be in the form of a monitored voltage signal to a switch or relay.
C
Technician A says that if the engine rpm is constant, the scan tool should show a constant MAF grams-per-second reading. Technician B says that the MAF sensor can be frequency-producing sensor.
C
Technician A says that some TP sensors used with TAC systems are actually two or three TP sensors in one housing. Technician B says that some TP sensors are non-contact type Hall-effect sensors.
C
Technician A says that the TP sensor is a reference voltage sensor. Technician B says the oxygen sensor is a voltage-generating sensor.
C
Technician A says that the air intake temperature (IAT) sensor signal is very similar to the engine coolant temperature sensor signal. Technician B says that cold intake air is denser than warm air.
C
Technician A says that the intake air temperature (IAT) sensor voltage should be about 0.28 volt at 260°F . Technician B says that the voltage should be about 2.51 volts at 100°F .
C
While discussing ECT sensor diagnosis, Technician A says that a defective ECT sensor may cause hard cold engine starting. Technician B says that a defective ECT sensor may cause improper operation of emission control devices. Who is correct?
C
While discussing a clutch pedal position (CPP) sensor, Technician A says that the CPP sensor tells the ECM if the clutch is engaged or disengaged. Technician B says that a defective CPP sensor also affects MAF sensor calculations.
C
While discussing magnetic pulse generator tests, Technician A says that an ohmmeter can be used to test the resistance of the coil. Technician B says that the voltage generated by the sensor can be measured by connecting a voltmeter across the sensor's terminals.
C
While discussing the testing of sensors, Technician A says that sensors can be tested with a scan tool. Technician B says that a breakout box is available for some vehicles to test sensor outputs. Who is correct?
C
Technician A says that air-fuel (AF) ratio sensors can be diagnosed with a voltmeter. Technician B says that the air-fuel (AF) ratio sensor is a Hall-effect sensor.
D
Technician A says that the intake air temperature (IAT) sensor is a voltage-generating sensor. Technician B says that the MAF sensor is a reference voltage sensor.
D
Technician A says that the oxygen sensor produces a high-voltage signal when the exhaust is lean. Technician B says that the oxygen sensor produces a low-voltage signal when the exhaust is rich.
D
While discussing trouble codes, Technician A says that hard failures are those that have occurred in the past, but were not present during the last test of the PCM. Technician B says that history or intermittent codes are those that were detected the last time the PCM tested the circuit.
D
When observing o2 sensor voltages
It is important to monitor both the maximum voltage levels attained and the frequency of the signal.
Thermistors utilize
a conductor or a pair of conductors separated by a semiconductor, temperature changes increase or decrease the resistance.
The code or symbol shown above depicts:
antistatic measures and devices should be utilized.
Vehicle speed sensors (VSS)
have an internal resistance that can be checked with an ohm meter.
Voltage generating sensors
induce or produce their own voltage that is strictly engineered via their construction, and send it as a data input signal to the computer.
Feedback
is the return signal to the computer as a data input.
MAF sensors produce a signal with a frequency that, when monitored
should show as a constant grams per second reading at a steady rpm rate.
Reference voltage sensors operate on
the premise that a reference voltage of a specific value is sent to the sensor and then the conditions acting on the sensor cause it to change or modify the voltage signal and send it back to the computer as a data input.
Mass airflow sensors (MAF) and manifold absolute pressure sensors (MAP) give the computer
the same information but by a different means of data collection and measuring different aspects of the same substance. This requires each computer to be programed to decipher one type of signal through a particular formula or the other signal with a different formula.
Piezoelectric sensors
use a quartz crystal that is acted on by pressure to generate their voltage signal.
Hall effect sensors
use an input voltage signal that is affected by a permeant magnet. The magnets flux field travels through the hall layer, (thin semiconductor layer [usually disc shaped] made of gallium arsenate crystal) this is lavered with a shutter wheel which blocks the flux field at intended intervals. The hall layer produces a specific voltage signal that is pulsed by the shutter wheel ultimately sending that signal to the computer.
02 sensors
use zirconium dioxide to chemically react with oxygen to produce their voltage signal.
Wheatstone bridges
utilize a series parallel circuit of fixed resistors and a variable resistor to modify reference voltage.
Potentiometers are
variable resistors that use a mechanical blade and grid resistor to create and analog increase or decrease in resistance in relation to the position of the blade on the resistive element.
