Information Sensors/Switches Description

3X Reference PCM Input

The PCM uses a signal from the ignition control module in order to calculate the engine RPM and the crankshaft position at engine speeds above 1200 RPM. The PCM also uses the pulses on this circuit in order to initiate the injector pulses. If the PCM receives no pulses on this circuit, the PCM will use the 18X reference signal circuit for fuel control and for ignition control. The engine will continue to start and will run using only the 18X reference signal. DTC P1374 will set.

18X Reference PCM Input

The PCM uses a signal from the ignition control module in order to calculate the engine RPM and the crankshaft position at engine speeds below 1200 RPM. The PCM also uses the pulses on this circuit in order to initiate the injector pulses. If the PCM receives no pulses on this circuit, DTC P0336 will set. The PCM will use the 3X reference signal circuit at all times for fuel control and for ignition control. The engine will continue to start and will run using only the 3X reference signal.

A/C Refrigerant Pressure Sensor

The A/C refrigerant pressure sensor signal indicates high side refrigerant pressure to the PCM. The PCM uses this information in order to perform the following functions:

• To adjust the idle air control valve
• To compensate for the higher engine loads that are present with the high A/C refrigerant pressures
• To control the cooling fans

A fault in the A/C refrigerant pressure sensor signal will cause DTC P0530 to set.

A/C Request PCM Input

The A/C request signal indicates to the PCM that an A/C mode is selected at the A/C control head. The PCM uses this information in order to adjust the idle speed before turning ON the A/C clutch. If this signal is not available to the PCM, the A/C compressor will be inoperative.

Crankshaft Position (CKP) Sensor

The crankshaft position sensor provides a signal that the ignition control module uses in order to calculate the ignition sequence. The ignition control module also uses the crankshaft position sensor signals in order to initiate the 18X reference pulses and the 3X reference pulses. The PCM uses these pulses as a reference, in order to calculate the RPM and the crankshaft position.

Camshaft Position (CMP) Sensor and CAM Signal

The camshaft position sensor sends a cam signal to the PCM. The PCM uses the signal as a sync pulse in order to trigger the injectors in the proper sequence. The CAM signal is passed through the ignition control module. The signal is filtered and buffered by the ignition control module, but the signal is not processed in any other way. The PCM uses the CAM signal in order to indicate the position of the #1 piston during its power stroke. This allows the PCM to calculate a true Sequential Fuel Injection (SFI) mode of operation. If the PCM detects an incorrect CAM signal while the engine is running, DTC P0341 will set.

If the CAM signal is lost while the engine is running, the fuel injection system will shift to a calculated sequential fuel injection mode, based on the last fuel injection pulse. The engine will continue to run. The engine can be restarted, and the engine will run in the calculated sequential mode as long as the fault is present. There is a 1-in-6 chance of the injector sequence being correct.

Refer to DTC P0341 for further information.

Electronic Brake and Traction Control Module (EBTCM) / Electronic Brake Control Module (EBCM) - PCM UART Serial Data

The PCM uses the universal asynchronous receiving and transmitting (UART) serial data line in order to communicate with other components and systems within the vehicle. If the PCM does not receive the data from the Electronic Brake and Traction Control Module (EBTCM), or from the Electronic Brake Control Module (EBCM), the PCM will store DTC P1573, indicating the loss of communication with the ABS/TCS system.

The PCM also receives rough road information from the EBTCM/ EBCM on the Class 2 serial data circuit. The PCM uses the rough road information in order to enhance the misfire diagnostic by detecting the crankshaft speed variations that are caused by driving on rough road surfaces. This allows false misfire information to be rejected. The EBTCM/EBCM calculates the rough road information by monitoring the ABS wheel speed sensors. If a malfunction occurs which does not allow the EBTCM/EBCM to transmit the correct rough road information to the PCM while a misfire DTC is requesting the MIL, DTC P1380 will set. If a loss of communications occurs which causes the PCM to not receive the rough road information while a misfire DTC is requesting the MIL, DTC P1381 will set.

During certain conditions, the PCM can request the EBTCM to shut OFF, the traction control via the serial data. The following DTCs will cause traction control to be disabled, cause an ABS/TCS DTC to be set, and cause the Traction OFF lamp to illuminate:

• DTC P0101--Mass Air Flow System Performance
• DTC P0102--Mass Air Flow Sensor Circuit Low Frequency
• DTC P0103--Mass Air Flow Sensor Circuit High Frequency
• DTC P0171--Fuel Trim System Lean
• DTC P0172--Fuel Trim System Rich
• DTC P0300--Engine Misfire Detected
• DTC P0336--18x Reference Signal Circuit
• DTC P0341--Camshaft Position Sensor Performance
• DTC P1374--3X Reference Circuit

Engine Coolant Temperature (ECT) Sensor

The engine coolant temperature (ECT) sensor is a thermistor, or a resistor, which changes value based on the temperature. The ECT sensor is mounted in the engine coolant stream. A low coolant temperature produces a high resistance (100,700 ohms at -40°C/-40°F). A high coolant temperature causes a low resistance (70 ohms at 130°C/266°F).

The PCM supplies a 5-volt signal to the engine coolant temperature sensor through a resistor in the PCM, and measures the voltage. The voltage will be high when the engine is cold, and low when the engine is hot. By measuring the voltage, the PCM calculates the engine coolant temperature. The scan tool displays the ECT in degrees. After engine startup, the temperature should rise steadily to approximately 90°C (194°F), then stabilize when thermostat opens. If the engine has not been run for several hours, the ECT and the intake air temperature displays should be similar.

The ECT affects most systems that the PCM controls. A hard fault in the engine coolant sensor circuit should set DTC P0117 or DTC P0118. An intermittent fault should set a DTC P1114 or DCT P1115. This section also contains a specification table in order to check for sensor resistance values that are relative to the temperature.

Exhaust Gas Recirculation (EGR) Pintle Position Sensor

The PCM monitors the exhaust gas recirculation (EGR) valve pintle position input in order to ensure that the valve properly responds to the commands from the PCM, and to detect a fault if the pintle position sensor circuit is open or shorted. If the PCM detects an excessively low EGR feedback signal voltage, where the pintle position feedback is open or shorted, DTC P0405 will set.

The linear EGR valve is controlled by an ignition positive driver and ground circuit within the PCM. The PCM can detect an electrical malfunction in the ignition positive or ground circuit. If an electrical malfunction occurs, DTC P0403 will set.

When the ignition switch is turned ON, the PCM learns the EGR closed valve pintle position. When the PCM commands the EGR valve closed, the learned EGR closed valve pintle position is compared to the actual EGR position. If the actual EGR position indicates that the EGR valve is still open, DTC P1404 will set.

When the PCM commands the EGR valve open, the actual EGR position is compared to the desired EGR Position. If the actual EGR Position is 15 percent less than the desired EGR position when the PCM is commanding the EGR valve opened, DTC P0404 will set.

Engine Oil Level Switch

The Engine Oil Level (EOL) switch is a simple float switch that is grounded when the engine oil level is OK. When the ignition is first turned ON, the PCM briefly commands ON the Low Oil Level lamp in order to test the bulb. The PCM also tests the engine oil level switch circuit at startup. If the engine has been running, the PCM performs a test routine that is based on the ECT in order to ensure that the engine oil has drained back into the sump before testing the state of the engine oil level switch. If the ECT is between 15°C (59°F) and 130°C (266°F), the PCM compares the ECT at the last key OFF to the ECT at the current key ON. If the difference between the recorded temperature values is at least 12°C (54°F), the PCM will test the engine oil level.

Fuel Level Sensor PCM Input

The fuel level sensor input to the PCM is used to determine if the fuel level in the tank is correct to run the EVAP diagnostic tests. In order to ensure sufficient volume in the tank to begin the various diagnostic tests, the fuel level must be between 15 percent and 85 percent.

Fuel Tank Pressure Sensor

The fuel tank pressure sensor is used in order to detect the vacuum decay and the excess vacuum during the enhanced EVAP diagnostic routine

Heated Oxygen Sensors

The fuel control Heated Oxygen Sensor (HO2S 1) is mounted in the exhaust manifold, where the sensor can monitor the oxygen content of the exhaust gas stream. The oxygen in the exhaust gas reacts with the sensor in order to produce a voltage output. This voltage should constantly fluctuate from approximately 100 mV at a high oxygen content and a lean mixture, to 900 mV at a low oxygen content and a rich mixture. A scan tool can monitor the HO2S voltage. By monitoring the voltage output of the oxygen sensor, the PCM calculates the fuel mixture command for the injectors. A lean mixture and a low HO2S voltage will produce a rich command. A rich mixture and a high HO2S voltage will produce a lean command.

An open HO2S 1 circuit should set a DTC P0134. The scan tool will display a constant voltage between 400 mV and 500 mV. A constant voltage below 300 mV in the sensor circuit, with the circuit grounded, should set DTC P0131. A constant voltage above 800 mV in the circuit should set DTC P0132. A fault in the HO2S 1 heater circuit should cause DTC P0135 to set. The PCM can also detect HO2S response problems. If the response time of an HO2S is too slow, the PCM will store a DTC that indicates degraded HO2S performance.

A 3-way catalytic converter controls the emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx). The catalyst within the converter promotes a chemical reaction, which oxidizes the HC and the CO in the exhaust gas. The catalytic converter converts these emissions into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM can monitor this process using the HO2S 1 and the HO2S 2 heated oxygen sensors.

The HO2S 1 sensor produces an output signal that indicates the amount of oxygen in the exhaust gas that is entering the 3-way catalytic converter. The HO2S 2 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalyst's ability to efficiently convert the exhaust gases. If the catalyst is operating efficiently, the HO2S 1 signal will be much more active than the signal that the HO2S 2 sensor produces. The catalyst monitor sensors operate the same as the fuel control sensors.

Although the HO2S 2 sensor's main function is catalyst monitoring, the sensor also plays a limited role in fuel control. If the sensor output indicates a voltage that is above or below the 450-millivolt bias voltage for an extended time, the PCM will make a slight adjustment to fuel trim in order to ensure that the fuel delivery is correct for catalyst monitoring.

A problem with the HO2S 2 signal circuit should set DTC P0137, DTC P0138, or DTC P0140. A fault in the heated oxygen sensor heater element or in its ignition feed or ground will result in slower oxygen sensor response. This may cause erroneous catalyst monitor diagnostic results. A fault in the HO2S 2 heater circuit should cause DTC P0141 to set.

Intake Air Temperature Sensor

The Intake Air Temperature (IAT) sensor is a thermistor which changes value based on the temperature of the air entering the engine. A low temperature produces a high resistance (100,700 ohms at -40°C/-40°F). A high temperature causes a low resistance (70 ohms at 130°C/266°F). The PCM supplies a 5-volt signal to the sensor through a resistor in the PCM, and measures the voltage. The voltage will be high when the incoming air is cold. The voltage will be low when the air is hot. By measuring the voltage, the PCM calculates the incoming air temperature.

The IAT sensor signal is used in order to adjust the spark timing according to the incoming air density. The scan tool displays the temperature of the air that enters the engine. The scan tool reading should be close to the ambient air temperature when engine is cold. The scan tool reading should rise when the underhood temperature increases. If the engine has not run for several hours, the IAT sensor temperature and the ECT should be similar. A failure in the IAT sensor circuit will set DTC P0112 or DTC P0113.

Reference Low

This is a ground circuit for the digital RPM counter inside the PCM, but the wire is connected to engine ground only through the Ignition Control Module. Although this circuit is electrically connected to the PCM, it is not connected to ground at the PCM. The PCM compares the voltage pulses on the 18X reference circuit and on the 3X reference input circuits to any pulses on this circuit. The PCM ignores the pulses that appear on both circuits. If the circuit is open, or if the circuit is connected to ground at the PCM, it may cause faulty engine performance, and can cause a MIL with no DTC set.

Knock Sensors

The knock sensors detect abnormal vibration, or spark knocking, in the engine. The sensors are mounted in the engine block, near the cylinders. The knock sensors produce an AC voltage signal during all engine operating conditions. The PCM adjusts the Ignition Control (IC) spark timing, based on the amplitude and the frequency of the KS signal that the PCM receives.

The PCM contains integrated Knock Sensor (KS) diagnostic circuitry. The PCM uses the circuitry in order to diagnose the KS sensors and the related wiring. The PCM calculates an average voltage of each knock sensor's signals, and takes instantaneous signal voltage readings. The PCM uses the instantaneous signal voltage readings in order to determine the state of the knock sensor circuitry. If the knock sensor system is operating normally, the PCM should monitor instantaneous KS signal voltage readings that vary outside a voltage range above and below the calculated average voltage. If the PCM malfunctions in a manner which will not allow proper diagnosis of the KS circuit, DTC P0325 will set. DTC P0327 and DTC P0332 are designed to diagnose the knock sensors and the related wiring, so KS system problems should set a DTC.

Mass Air Flow Sensor

The Mass Air Flow (MAF) sensor measures the amount of air which passes through the throttle body. The PCM uses this information in order to determine the operating condition of the engine, in order to control the fuel delivery. A large quantity of air indicates acceleration. A small quantity of air indicates a deceleration or an idle.

The scan tool displays the MAF value in grams per second (gm/s). During idle, the MAF should be between 4 gm/s and 7 gm/s on a fully-warmed engine. The values should change quickly during acceleration. The values should remain fairly stable at any specific RPM. A MAF sensor malfunction or a MAF signal circuit problem will set DTC P0101, DTC P0102, or DTC P0103.

Manifold Absolute Pressure Sensor (VIN K)

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 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 more than 4 volts with the key ON, leaving the engine off, 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 be set. A signal voltage higher than the possible range of the sensor will set DTC P0108. An intermittent low or high voltage will set DTC P1107 or DTC P1106 respectively.

Manifold Absolute Pressure Sensor (VIN 1)

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 that is relative to the pressure changes in the manifold. With the key ON, engine not running, the MAP sensor signal voltage to the PCM varies between 1.5-2.5 volts. With the engine running, the MAP sensor voltage to the PCM varies from less than 2 volts at idle (low manifold absolute pressure - high vacuum) to more than 4 volts 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 be set. A signal voltage that is higher than the possible range of the sensor will set DTC P0108. An intermittent low or high voltage will set DTC P1107 or DTC P1106 respectively.

TCC Brake Switch

The TCC brake switch signal indicates when the brake pedal is applied. The PCM uses the TCC brake switch information to control the Transaxle torque converter clutch.

Throttle Position Sensor

The Throttle Position (TP) sensor is a potentiometer that is connected to the throttle shaft on the throttle body. By monitoring the voltage on the signal line, the PCM calculates the throttle position. When the throttle valve angle during accelerator pedal movement, the TP sensor signal also changes. During closed throttle, the output of the TP sensor is low. When the throttle valve opens, the TP sensor voltage increases. During Wide Open Throttle (WOT), the TP sensor voltage should be more than 4 volts. The PCM calculates the fuel delivery based on the throttle valve angle.

A broken or loose TP sensor may cause intermittent bursts of fuel from an injector. This condition will cause an unstable idle because the PCM thinks the throttle is moving. A hard failure in the TP sensor 5-volt reference or signal circuits should set either a DTC P0122 or DTC P0123. A hard failure with the TP sensor ground circuit may set DTCs P0123 and P0117. If a DTC sets, the PCM uses an artificial default value that is based on the engine RPM and the mass air flow for the throttle position. Some vehicle performance will return. A high idle may result when either DTC P0122 or DTC P0123 is set.

The PCM can detect intermittent TP sensor faults. DTC P1121 or DTC P1122 will set if an intermittent high or low circuit failure is being detected. The PCM can also detect a shifted TP sensor. The PCM monitors throttle position, and compares the actual TP sensor reading to a predicted TP value that is calculated from the engine speed. If the PCM detects an out-of-range condition, DTC P0121 will be set.

Transaxle Range Switch

The Transaxle Range Switch is part of the Transaxle Park/Neutral Position (PNP) switch mounted on the transaxle manual shaft. The 4 inputs from the transaxle range switch indicate to the PCM which position is selected by the Transaxle selector lever. This information is used for transmission shift control, ignition timing, EVAP canister purge, EGR and IAC valve operation. The combination of the four transaxle range input states determine the PCM commanded shift pattern. The input voltage level at the PCM is high (B+) when the transaxle range switch is open and low when the switch is closed to ground. The state of each input is represented on the scan tool as High voltage level, Low voltage level. The four parameters represent transaxle range switch Parity, A, B, and C inputs respectively. Valid transaxle range input combinations are shown in the Transaxle Range Switch Valid Input Combinations table.