The crank request circuit is used to signal the PCM that the ignition switch is in the START position. With the ignition switch in the UNLOCK, or RUN position, the PCM should detect zero volts on the crank request circuit. With the ignition switch in the START position, the crank request circuit applies a fused ignition voltage to the PCM. The PCM uses the crank request signal, and other inputs to decide whether, or not to allow starter operation.

The engine coolant temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The ECT sensor resistance varies from 100,000 ohms at -40°C (-40°F) to 70 ohms at 130°C (266°F). The PCM uses the ECT signal to calculate the coolant temperature. The PCM applies 5 volts to the ECT signal circuit through a pull-up resistor. When the engine coolant temperature is cold, the ECT sensor resistance is high. This causes the PCM to detect a high ECT signal voltage. When the engine coolant temperature increases, the sensor resistance lowers. The PCM should detect a low ECT signal voltage.

The scan tool displays the engine coolant temperature in degrees. After engine startup, the coolant temperature should steadily rise to approximately 90°C (194°F). Then, when the thermostat opens, the temperature should stabilize. If the engine has not been run for several hours (overnight), the ECT sensor and IAT sensor scan tool displays should read close to each other. Engine coolant temperature affects most PCM controlled systems. A hard fault in the ECT sensor circuit should set DTC P0117 or P0118. An intermittent fault should set DTC P1114 or DTC P1115. To check ECT sensor resistance relative to temperature, refer to the Temperature Versus Resistance table.

The EGR pintle position sensor is potentiometer used to indicate the amount of EGR valve opening. The PCM supplies the pintle position sensor with a 5 volt reference and a ground. The pintle position sensor provides a signal voltage to the PCM. By monitoring the voltage on the signal line, the PCM is able to determine if the EGR valve responds properly to commands from the PCM. As the EGR valve position changes, the pintle position signal voltage will change. With the EGR valve closed, the signal voltage is near 0 volts. However, the pintle position signal voltage increases as the EGR valve opens. When the PCM commands the EGR valve fully open, the pintle position signal voltage should be above 4 volts. If the PCM detects an excessively low pintle position signal voltage (circuit is open or shorted to ground), DTC P0405 will set.

When the ignition switch is in the RUN position, the PCM learns the EGR closed valve pintle position. When the PCM commands the EGR valve closed, the PCM compares the closed valve pintle position to the actual EGR position. If the actual EGR position indicates that the EGR valve is still open, DTC P1404 will set.

The PCM controls the EGR valve using an ignition voltage driver and ground located within the PCM. When the PCM commands the EGR valve open, the PCM compares the actual EGR position to the desired EGR position. If the actual EGR is less than the desired EGR by a calibrated amount, DTC P0404 will set. If an electrical malfunction occurs in the EGR valve control circuit, DTC P0403 will set.

The engine oil pressure sensor is a rheostat mounted in the oil filter adapter. The PCM supplies the sensor with a 5 volt reference and a ground. The sensor varies the 5 volt input voltage relative to the oil pressure at various engine speeds.

The PCM sends the oil pressure information via Class 2 to the instrument panel cluster (IPC). The IPC uses the information to control the oil pressure indicator.

The PCM monitors the fuel tank pressure sensor to detect vacuum decay and excess vacuum during the EVAP system tests. The fuel tank pressure sensor measures the difference between the air pressure (or vacuum) in the tank and the outside air pressure. The PCM supplies a 5 volt reference and a ground for the fuel tank pressure sensor. The fuel tank pressure sensor provides a signal to the PCM that ranges between 0.1 and 4.9 volts.

The fuel level sensor is a rheostat mounted on the fuel sender assembly. The PCM supplies the sensor with a 5 volt reference and a ground. The sensor varies the 5 volt input voltage based on the level of fuel in the tank. The PCM uses the signal voltage to calculate the amount of fuel in the tank.

The fuel level sensor is part of the fuel sender assembly. The PCM uses the fuel level input to make sure that the level of fuel in the tank is sufficient to run the EVAP tests. The PCM also sends the fuel level information via class 2 to the instrument panel cluster (IPC). The IPC uses the information to control the fuel level gauge.

The L-terminal circuit connects the generator to the PCM. The PCM applies ignition voltage to the L-terminal signal circuit through a resistor. The PCM should detect a low signal voltage input when the key is in the RUN position with the engine OFF, or when the charging system malfunctions. During engine operation, the PCM should detect a high signal voltage. The PCM monitors the L-terminal circuit for conditions outside the normal operating range. If the PCM detects an incorrect condition DTC P0621 will set and DTC P0622 may also set.

The F-terminal circuit connects the generator to the PCM. The PCM uses this circuit to monitor the pulse width modulation (PWM) of the field circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5 and 100 percent. The PCM monitors the F-terminal circuit for conditions outside the normal operating range. If the PCM detects an incorrect condition, DTC P0622 will set.

The heated oxygen sensors allow the PCM to maintain an air/fuel ratio that provides the best performance, fuel economy, and emission control. There are three heated oxygen sensors mounted in the exhaust gas stream. HO2S bank 1 sensor 1 and bank 2 sensor 1 are mounted in the right and left exhaust manifolds. HO2S bank 1 sensor 2 is mounted in the exhaust pipe after the converter. These sensors produce a voltage due to the difference in oxygen content between the outside air and the exhaust gas stream.

The PCM uses the fuel control heated oxygen sensors (HO2S bank 1 sensor 1 and bank 2 sensor 1) to decide what fuel mixture command to give the fuel injectors. The PCM supplies a 450 millivolt reference voltage to the sensors. The sensors vary the reference voltage in response to the oxygen content in the exhaust gas stream. When the oxygen content is low (a rich condition), the PCM will detect a signal voltage near 900 millivolts. When the oxygen content is high (a lean condition), the PCM will detect a signal voltage near 100 millivolts. The PCM adjusts the injector pulse width to correct for a rich or a lean condition. The PCM uses HO2S bank 1 sensor 2 to determine how well the three-way catalyst is controlling emissions. The PCM compares the signals from HO2S bank 1 sensor 1 and bank 2 sensor 1 to the signal from HO2S bank 1 sensor 2. If the catalyst is operating efficiently, the PCM should detect a HO2S bank 1 sensor 2 signal less active than the signals from HO2S bank 1 sensor 1 and bank 2 sensor 1.

The intake air temperature (IAT) sensor is a thermistor integrated with the mass air flow (MAF) sensor. The IAT sensor resistance varies from 100,000 ohms at 40°C (40°F) to 70 ohms at 130°C (266°F). The PCM uses the IAT signal to calculate the intake air temperature. The PCM applies 5 volts to the IAT signal circuit through a pull-up resistor. When the intake temperature is cold, the IAT sensor resistance is high. This causes the PCM to detect a high IAT signal voltage. As the underhood temperatures increase, the IAT sensor resistance lowers. The PCM should detect a low IAT signal voltage.

The scan tool displays the intake air temperature in degrees. The IAT sensor display should read close to ambient air temperature when the engine is cold. As the underhood temperature increases, the IAT sensor display should also increase. If the engine has not been run for several hours (overnight), the IAT sensor and ECT sensor scan tool displays should read close to each other. A hard fault in the IAT sensor circuit should set DTC P0112 or P0113. An intermittent fault should set DTC P1111 or DTC P1112. To check IAT sensor resistance relative to temperature, refer to the Temperature Vs Resistance table.

The manifold absolute pressure (MAP) sensor responds to changes in intake manifold pressure. The PCM supplies a 5 volt reference and a ground for the MAP sensor. The MAP sensor provides a signal to the PCM relative to the pressure changes in the manifold. The MAP sensor signal voltage to the PCM varies from below 2 volts at idle (low manifold absolute pressure - high vacuum) to above 4 volts with the key ON, engine not running or at wide-open throttle (high manifold absolute pressure - low vacuum).

If the PCM detects a voltage that is lower than the possible range of the MAP sensor, DTC P0107 will set. A signal voltage higher that the possible range of the MAP sensor will set DTC P0108. An intermittent low or high voltage will set DTC P1107 or P1106 respectively.

The mass air flow (MAF) sensor measures the amount of air flow into the engine in a given time. The MAF sensor produces a signal as air passes through the sensor and into the engine. The amount of air flow determines the frequency of the signal. If the air flow through the sensor increases, the frequency of the signal will increase. If the air flow through the sensor decreases, the frequency of the signal will decrease. Normally, the frequency will vary from approximately 2000 Hertz at idle to about 10,000 Hertz at maximum engine load. The PCM uses the MAF sensor information to provide the correct fuel delivery for all engine operating conditions.

The scan tool displays the MAF value in grams per second (g/s). At idle, the scan tool should display a MAF value of 4 g/s - 7 g/s on a fully warmed engine. Values should change rather quickly on acceleration. However, the values should remain fairly stable at any given RPM.

If the PCM detects a signal frequency lower than the possible range of a normally operating MAF sensor, DTC P0102 will set. If the PCM detects a signal frequency higher than the possible range of a normally operating MAF sensor, DTC P0103 will set. If the actual MAF sensor frequency does not match a PCM calculated MAF value, DTC P0101 will set.

The throttle position (TP) sensor is potentiometer used to indicate the amount of throttle opening. The PCM supplies the TP sensor with a 5 volt reference and a ground. The TP sensor provides a signal voltage to the PCM relative to throttle blade angle. By monitoring the voltage on the signal line, the PCM calculates throttle position. As the throttle valve changes (accelerator pedal moved), the TP sensor output voltage will change. With the throttle closed, the signal voltage is low (below 1 volt). However, the TP sensor voltage increases as the throttle valve opens. At wide open throttle (WOT), the TP sensor voltage should be above 4 volts.

The TP signal is one of the most important sensor inputs used by the PCM for controlling fuel and most of the PCM-controlled outputs. A malfunction in the TP sensor or related wiring should set DTC P0122 or DTC P0123. An intermittent condition will set DTC P1121 or DTC P1122. If the actual TP sensor signal does not match a PCM calculated TP value, DTC P0121 will set.

The PCM uses a knock sensor (KS) to detect abnormal vibration in the engine (detonation/spark knocking). The knock sensor is mounted in the engine block, under the intake manifold. The knock sensor produces an AC signal at all engine speeds and loads. The PCM then adjusts the spark timing based on the amplitude and frequency of the KS signal.

A knock sensor module is no longer used to diagnose the knock sensor system. The circuitry is integrated into the PCM. The PCM uses the knock sensor to determine the amount of normal engine noise (noise channel) for a wide range of engine speeds and loads. The PCM compares the actual knock sensor signal to the learned noise channel.

The PCM uses the input from the torque converter clutch (TCC) and extended travel brake switches to determine the state of the brake pedal (applied or released). The PCM uses the TCC switch input to mainly control the transaxle torque converter clutch (TCC). The PCM sends the extended travel brake switch input, via class 2, to the EBTCM for braking and traction control management. The switches receive power through a fused ignition feed (hot in RUN and START). With the ignition in the RUN or CRANK position, and the brakes not applied, the PCM should detect ignition voltage. With the brakes applied, the PCM should detect zero volts.

The cruise control module also uses the input from the TCC brake switch. The cruise control system will disengage cruise operation when the TCC brake switch input indicates that the brakes are applied.