The A/C refrigerant pressure sensor signal indicates thehigh side refrigerant pressure to the powertrain control module (PCM). The PCM uses this information to adjust the idle air control (IAC) valve to compensate for the higher engine loads present with a high A/C refrigerant pressure and to control the cooling fans. A fault in the A/C refrigerant pressure sensor signal will cause a DTC P0530 to set.

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 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.

The CKP sensor used on this engine is actually 2 sensors within a single housing. Each sensor has a separate power, ground, and signal circuit. The PCM supplies 12 volts to both sensors. The PCM provides the ground path, or sensor return circuit, from both sensors. The power and ground circuits are also connected to the camshaft position (CMP) sensor. Two separate signal circuits connect the CKP sensor and the PCM.

The PCM can use 3 different modes of decoding the crankshaft position. During normal operation, the PCM performs an Angle Based calculation using both signals to determine the crankshaft position. The dual sensor allows the engine to run even if one signal is lost. If either signal is lost, the PCM switches to a Time Based method of calculating the crankshaft position. If the system is operating in Time A mode, the PCM is using only the signal from Sensor A. Time B indicates that the Sensor B signal is being used. If the lost signal is restored, the PCM will continue to operate in Time Based mode for the remainder of the current key cycle. The PCM will revert back to the Angle Based mode on the next start if the fault is no longer present. The scan tool can display the Crank Position Sensing Decode Mode. A problem with sensor A will set a DTC P0335. A problem with sensor B will set a P0385.

The CMP sensor signal, when combined with the CKP sensor signal, enables the PCM to determine exactly which cylinder is on a firing stroke. The PCM can then properly synchronize the ignition system, the fuel injectors, and the knock control. The CMP sensor has a power, ground, and signal circuit. The PCM supplies 12 volts to the sensor. The PCM provides the ground path, or sensor return circuit, from the sensor. The power and ground circuits are also connected to the CKP sensor. If a problem is detected with the CMP circuit, a DTC P0340 will set.

The PCM uses the Class 2 serial data line to communicate with various components and systems within the vehicle. The PCM ensures that the communication remains established by monitoring the Class 2 serial data circuit for state of health (SOH) messages from the other devices using the circuit. If the PCM detects a loss of the SOH serial data message from the EBTCM, the PCM will store a DTC P1602.

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 to enhance the misfire diagnostic by detecting any crankshaft speed variations caused by driving on rough road surfaces. This allows any 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, a 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, a DTC P1381 will set.

Under certain conditions, the PCM has the ability to request the EBTCM to shut OFF the traction control via the Class 2 serial data. The following DTCs will cause the traction control to be disabled, an ABS/TCS DTC to be set, and the Traction Off lamp to be illuminated:

Refer to ABS/TCS in Antilock Brake System for information regarding the ABS/TCS operation.

The engine coolant temperature (ECT) sensor is a thermistor, which is a resistor that changes value based on the temperature. The engine coolant temperature sensor is mounted in the engine coolant stream. A low ECT produces a high resistance, while a high coolant temperature causes a low resistance..

The PCM supplies a 5 volt signal to the ECT 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 ECT. The scan tool displays the ECT in degrees. After engine startup, the temperature should rise steadily to about 90°C (194°F) and then stabilize when the thermostat opens. If the engine has not been run for several hours or overnight, the ECT and the intake air temperature (IAT) displays should be close to each other.

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

The PCM monitors the EGR valve pintle position input to ensure that the valve responds properly to 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, a DTC P0405 will set.

The linear EGR valve is controlled by using an ignition positive driver and ground circuit within the PCM. The driver has the ability to detect an electrical malfunction in the ignition positive or the ground circuit. If an electrical malfunction occurs, a 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, a DTC  P1404 will set.

When the PCM commands the EGR valve open, the actual EGR position is compared with 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, a DTC P404 will set.

The engine oil level 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 commands the Low Oil Level lamp ON for approximately 3 seconds test the bulb. The PCM also checks the engine oil level switch circuit at startup. If the engine has been running, the PCM performs a test routine based on the ECT to ensure that the engine oil has drained back into the sump before checking 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.

The PCM applies battery voltage through a pull up resistor to the engine oil pressure switch circuit. The PCM monitors the applied voltage on the engine oil pressure switch circuit. If the ignition switch is turned ON with the engine not running, or the engine oil pressure is less than 35 kPa (5 psi), the engine oil pressure switch grounds the PCM voltage input. The PCM sends the engine oil pressure information via Class 2 serial data to the instrument panel cluster (IPC). The IPC controls the engine oil pressure indicator.

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. To ensure a sufficient volume in the tank to begin the various diagnostic tests, the fuel level must be between 15 and 85 percent. Refer to Evaporative Emission Control System Operation Description for a complete description of the EVAP system.

The fuel tank pressure sensor is used to detect any vacuum decay or excess vacuum during the enhanced EVAP diagnostic routine. Refer to Evaporative Emission Control System Operation Description for a complete description of the EVAP system.

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 present in the exhaust gas reacts with the sensor to produce a voltage output. This voltage should constantly fluctuate from approximately 100 mV at a high oxygen content to 900 mV at a low oxygen content. The heated oxygen sensor voltage can be monitored with a scan tool. By monitoring the voltage output of the oxygen sensor, the PCM calculates what fuel mixture command to send to the injectors.

An open HO2S 1 circuit should set a DTC P0134, and the scan tool will display a constant voltage between 400 - 500 mV. A constant voltage of less than 175 mV in the sensor circuit should set a DTC P0131, while a constant voltage of more than 975 mV in the circuit should set a DTC P0132. A fault in the HO2S 1 heater circuit should cause a DTC P0135 to set. The PCM can also detect HO2S response problems. If the response time of an HO2S is determined to be too slow, the PCM will store a DTC that indicates a degraded HO2S performance.

To control the emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a 3-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction that oxidizes the HC and CO present in the exhaust gas, converting the HC and CO into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx, converting the NOx to nitrogen. The PCM has the ability to monitor this process using the HO2S 1 and the HO2S 2.

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

Although the main function of the HO2S 2 is catalyst monitoring, the sensor also plays a limited role in the fuel control. If the sensor output indicates a voltage of more than or less than the 450 millivolt bias voltage for an extended period of time, the PCM will make a slight adjustment to the fuel trim to ensure that the fuel delivery is correct for the catalyst monitoring.

A problem with the HO2S 2 signal circuit should set a DTC P0137, P0138, or P0140, depending on the specific condition. A fault in the heated oxygen sensor heater element or the heater element's 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 a DTC P0141 to set.

The heated oxygen sensors (HO2S) require an air reference for proper operation. The air reference is supplied through the HO2S wiring. Inspect the HO2S wires and connections for breaks or contamination. Do not use solder to repair HO2S wiring. Solder will obstruct the air path. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems for proper repair procedures.

The intake air temperature (IAT) sensor is a thermistor which changes value based on the temperature of air entering the engine. A low air temperature produces a high resistance , while a high temperature causes a low resistance. 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, and low when the air is hot. By measuring the voltage, the PCM calculates the incoming air temperature.

The IAT sensor signal is used in calculating the incoming air density. The scan tool displays the temperature of the air entering the engine, which should read close to the ambient air temperature when the engine is cold, and rise as the underhood temperature increases. If the engine has not been run for several hours or overnight the IAT and the engine coolant temperature should read close to each other. A failure in the IAT sensor circuit should set a DTC P0112 or DTC P0113.

The knock sensor detects abnormal vibration or spark knocking in the engine. The knock sensor produces an AC voltage signal under all engine operating conditions. The PCM adjusts the ignition control (IC) spark timing based on the amplitude and the frequency of the KS signal being received.

The PCM contains integrated KS diagnostic circuitry. The PCM uses the circuitry to diagnose the KS and the related wiring. During normal operation the PCM calculates the average voltage of the knock sensor signal. If the knock sensor system is operating normally, the PCM should monitor a KS signal voltage varying over 0.5 volt more than and less than the calculated average voltage. If the PCM malfunctions in a manner which will not allow a correct diagnosis of the KS circuit, a DTC 325 will set.

DTC P0327 applies to the knock sensor and related wiring.

Refer to Knock Sensor (KS) System Description for a complete description of the knock sensor system.

The mass air flow (MAF) sensor measures the amount of air which passes through the throttle body. The PCM uses this information to determine the operating condition of the engine and to control fuel delivery. A large quantity of air indicates acceleration or a high engine load, while a small quantity indicates deceleration or an idle.

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

The manifold absolute pressure (MAP) sensor responds to changes in the intake manifold pressure. The MAP sensor signal voltage to the PCM varies from less than 2 volts at idle to more than 4 volts with the key ON and engine not running or at wide-open throttle. The MAP sensor is used to determine any manifold pressure changes while the linear EGR flow test diagnostic is being run (refer to DTC P0401), to determine engine vacuum level for other diagnostics, and to determine the barometric pressure (BARO).

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

The TCC brake switch signal indicates when the brake pedal is applied. The TCC brake switch information is used by the PCM mainly to control the transaxle torque converter clutch. Refer to Transmission Component and System Description in Automatic Transaxle.

The transaxle fluid temperature sensor is a thermistor which changes value based on the temperature of the transaxle fluid. A high transaxle fluid temperature may cause the vehicle to operate in Hot Mode. While in Hot Mode, the shift points may be altered, the 4th gear disabled, and the TCC forced ON in 2nd gear.

A failure in the TFT sensor or the associated wiring should cause a DTC P0712 or P0713 to set. In this case, a value based on the engine coolant temperature will be substituted for the TFT sensor value, and the transaxle will operate normally. Refer to Transmission Component and System Description in Automatic Transaxle.

The throttle position (TP) sensor is a potentiometer connected to the throttle shaft on the throttle body. By monitoring the voltage on the signal line, the PCM calculates the throttle position. As the throttle valve angle is changed when the accelerator pedal is moved, the TP sensor signal also changes. At a closed throttle position, the output of the TP sensor is low. As the throttle valve opens, the TP sensor voltage increases so that at 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 and 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. Once a DTC is set, the PCM will use an artificial default value based on the engine RPM and the mass air flow for the throttle position, and some vehicle performance will return. A high idle may result when either a DTC P0122 or a DTC P0123 is set.

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

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 the transmission shift control, the ignition timing, the EVAP canister purge, and the EGR and IAC valve operations. The combination of the 4 transaxle range input states determines the PCM commanded shift pattern. The input voltage level at the PCM is high 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 4 parameters represent transaxle range switch Parity, A, B, and C inputs respectively. The valid transaxle range input combinations are shown in the Transaxle Range Switch Valid Input Combinations table.