Engine Controls Self-Diagnostics - 3.4L: Overview Pontiac Montana I

MODEL IDENTIFICATION

Vehicle model is identified by the fifth character of Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION table.

MODEL IDENTIFICATION

Description

This procedure satisfies enable criteria necessary to execute all monitor diagnostics, and complete trips for those particular diagnostics. When all diagnostic tests have been completed, I/M System Status indicators are set to YES. Perform this test when more than one or all I/M System Status indicators are set to NO.

Ensure vehicle meets the following conditions before performing procedure

1. Barometric pressure is greater than 65 kPa.
2. Engine coolant temperature is less than 86°F (30°C).
3. Intake air temperature is less than 90°F (32°C).
4. Difference between intake air temperature and engine coolant temperature is 7°F (5°C) or less.
5. Battery voltage is 10-18 volts.
6. Fuel level is 1/4-3/4 tank.

This test should satisfy enable criteria necessary to execute I/M readiness diagnostics for secondary Air Injection (AIR) system. Test may be used to set I/M SYSTEM STATUS indicators to YES. Ensure vehicle meets requirements listed in enable criteria before performing test.

This test should satisfy enable criteria necessary to execute I/M readiness diagnostics for the catalyst system. Test may be used to set I/M SYSTEM STATUS indicators to YES. Ensure vehicle meets requirements listed in enable criteria before performing test.

This test should satisfy enable criteria necessary to execute I/M readiness diagnostics for the Exhaust Gas Recirculation (EGR) system. Test may be used to set I/M SYSTEM STATUS indicators to YES. Ensure vehicle meets requirements listed in enable criteria before performing test.

This test should satisfy enable criteria necessary to execute I/M readiness diagnostics for the evaporative emission system. Test may be used to set I/M SYSTEM STATUS indicators to YES. Ensure vehicle meets requirements listed in enable criteria before performing test.

Purpose of this test is to satisfy enable criteria necessary to execute I/M readiness diagnostics for heated oxygen sensor/oxygen sensor system. Test may be used to set I/M system status indicators to YES. Ensure vehicle meets enable criteria before performing test.

Purpose of this test is to satisfy enable criteria necessary to execute I/M readiness diagnostics for heated oxygen sensor heater system. Test may be used to set I/M system status indicators to YES. Ensure vehicle meets enable criteria before performing test.

Heated Oxygen Sensors (HO2S) are used to minimize amount of time required to enter closed-loop fuel control operation and to allow accurate catalyst monitoring. The HO2S No. 1 (HO2S 1) heater is powered directly from ignition 1 circuit. The HO2S 1 heater control circuit or heater ground is connected to PCM. PCM controls HO2S heater operation by grounding the control circuit via an internal solid state device called a driver. The driver supplies ground for the component being controlled. The driver for the HO2S 1 heater control circuit has the ability to measure amount of current drawn by the controlled device.

DTC will set when PCM detects that HO2S heater control circuit voltage is greater than the PCM internal driver capacity and condition is present for greater than 20 seconds.

Mass Airflow (MAF) sensor measures amount of air entering engine during a given time. PCM uses MAF sensor information for fuel delivery calculations. MAF sensor readings during acceleration are much higher than those during deceleration or idle.

PCM calculates what MAF sensor reading should be when received from sensor under certain conditions using engine speed (RPM), throttle position, and barometric pressure parameters. When certain test conditions are met, PCM will compare its calculated MAF value to actual value received from sensor. If difference is too great, DTC will set.

Mass Airflow (MAF) sensor measures amount of air entering engine during a given time. PCM uses MAF sensor information for fuel delivery calculations. MAF sensor readings during acceleration are much higher than those during deceleration or idle.

PCM calculates what MAF sensor reading should be when received from sensor under certain conditions using engine speed (RPM), throttle position, and barometric pressure parameters. When certain test conditions are met, PCM will compare its calculated MAF value to actual value received from sensor. DTC will set if signal from MAF sensor is less than a predetermined value.

Mass Airflow (MAF) sensor measures amount of air entering engine during a given time. PCM uses MAF sensor information for fuel delivery calculations. MAF sensor readings during acceleration are much higher than those during deceleration or idle.

PCM calculates what MAF sensor reading should be received from sensor under certain conditions using engine speed (RPM), throttle position, and altitude parameters. When these test conditions are met, PCM will compare its calculated MAF value to actual value received from sensor. DTC will set if PCM detects a frequency signal higher than the possible range of a normally operating sensor.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in intake manifold. The pressure changes occur based on engine load. MAP sensor has a 5-volt reference circuit, a low reference circuit, and signal circuit. The PCM supplies 5 volts to MAP sensor on the 5-volt reference circuit. PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to PCM on the signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. PCM should detect a high signal voltage at a high MAP, such as when ignition is on, with engine off, or at a Wide Open Throttle (WOT). Certain vehicle will also use MAP sensor to determine the Barometric Pressure (BARO). This occurs when ignition is on, with engine off. The BARO reading may also be updated whenever engine is operated at WOT. The PCM monitors MAP sensor signal for voltage outside of the normal range.

If PCM detects a MAP sensor signal voltage that is excessively low, this DTC will set.

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in intake manifold. The pressure changes occur based on engine load. MAP sensor has a 5-volt reference circuit, a low reference circuit, and signal circuit. The PCM supplies 5 volts to MAP sensor on the 5-volt reference circuit. PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to PCM on the signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. PCM should detect a high signal voltage at a high MAP, such as when ignition is on, with engine off, or at a Wide Open Throttle (WOT). Certain vehicles will also use MAP sensor to determine the Barometric Pressure (BARO). This occurs when ignition is on, with engine off. The BARO reading may also be updated whenever engine is operated at WOT. The PCM monitors MAP sensor signal for voltage outside of the normal range.

If PCM detects a MAP sensor signal voltage that is excessively high, this DTC will set.

The Intake Air Temperature (IAT) sensor is a thermistor which measures temperature of the air entering engine. The PCM applies 5 volts through a pull-up resistor. When intake air is cold, sensor resistance is high and PCM will monitor a high signal voltage on IAT sensor signal circuit. As intake air warms, sensor resistance drops, causing PCM to monitor a lower voltage. If PCM detects an excessively low IAT sensor signal voltage, high temperature indicated, DTC will set.

IAT sensor is a thermistor which measures the temperature of the air entering engine. The PCM applies 5 volts through a pull-up resistor. When intake air is cold, sensor resistance is high, and PCM will monitor a high signal voltage on IAT sensor signal circuit. As intake air warms, sensor resistance becomes lower, causing PCM to monitor a lower voltage. If PCM detects an excessively high IAT sensor signal voltage, a low temperature is indicated and DTC will set.

Engine Coolant Temperature (ECT) sensor is a variable resistor that measures temperature of engine coolant. The PCM supplies 5 volts to signal circuit. When coolant temperatures are low, resistance is high. When coolant temperatures are high, resistance is low. PCM uses this input for engine controls and enabling criteria for diagnostics. PCM will record amount of time engine is off. At restart, PCM will compare the temperature difference between the ECT and Intake Air Temperature (IAT). If temperature difference is not within the calculated amount, after the predetermined soak time, DTC will set. Before failing this test, PCM will check for presence of a block heater.

Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures temperature of engine coolant. The PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC will set.

Engine Coolant Temperature (ECT) sensor is a thermistor that varies resistance based on temperature. As temperature of sensor increases, resistance decreases. Low temperature will result in a high signal voltage. DTC will set when PCM detects an excessively high ECT signal voltage, which is a low temperature indication.

The Throttle Position (TP) sensor circuit provides a voltage signal that changes relative to throttle blade angle. PCM provides TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of TP sensor rotor from closed throttle position to Wide Open Throttle (WOT) position provides PCM with a signal voltage from less than one volt to greater than 4 volts through the TP sensor signal circuit. When conditions for running this DTC are met, PCM will use the MAP sensor to determine if the predicted operating range of TP sensor is correct.

A skewed MAP sensor may cause this DTC to set and should be tested for proper operation if TP sensor is determined to be operating properly and this DTC continues to set.

The Throttle Position (TP) sensor circuit provides a voltage signal that changes relative to throttle plate angle. PCM provides TP sensor with a 5-volt reference circuit and a low reference circuit. Rotation of TP sensor rotor from closed throttle position to Wide Open Throttle (WOT) position provides PCM with a signal voltage from less than one volt to greater than 4 volts through the TP sensor signal circuit.

DTC will set if PCM detects an excessively low signal voltage.

Throttle Position (TP) sensor measures amount of throttle opening. PCM uses TP sensor information for fuel delivery calculations. TP sensor readings during acceleration are much higher than those during deceleration or idle. DTC will set if TP sensor signal voltage is greater than 4.9 volts, with ignition on.

The Engine Coolant Temperature (ECT) sensor monitors coolant temperature. This input is used by the PCM for engine control and as an enabling criteria for some diagnostics. The airflow coming into the engine is accumulated and used to determine if engine has been driven within conditions that would allow engine coolant to heat up normally to the thermostat regulating temperature. If coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected.

DTC will set when there has been excessive time to reach a minimum coolant temperature required for closed-loop fuel control.

Engine Coolant Temperature (ECT) sensor monitors temperature of coolant. This input is used by PCM for engine control and as an enabling criteria for some diagnostics.

The airflow coming into engine is accumulated and used to determine if engine has been driven within conditions that would allow engine coolant to heat up normally to thermostat regulating temperature. If coolant temperature does not increase normally or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria may not run when expected.

DTC will set when engine coolant fails to reach a preset target temperature before a calculated airflow is accumulated.

PCM supplies a bias voltage of about 450 millivolts between HO2S high signal and low reference circuits. When measured with a 10 megohm DVOM, this may display as low as 350 millivolts. The oxygen sensor signal varies from about 800 millivolts when exhaust is rich, to about 50 millivolts when exhaust is lean.

DTC will set if signal amplitude of HO2S 1 sensor exceeds the no activity (DTC P0134) thresholds, but will not allow closed-loop operation.

The PCM supplies a bias voltage of about 450 millivolts between HO2S high signal circuit and HO2S low reference circuit. When measured with a 10-megohm DVOM, this may display as low as 350 millivolts. The oxygen sensor signal varies from about 800 millivolts when exhaust is rich, to about 50 millivolts when exhaust is lean.

DTC will set when HO2S 1 voltage remains excessively low for an extended time.

PCM supplies a bias voltage of about 450 millivolts between Heated Oxygen Sensor (HO2S) high signal circuit and the HO2S low reference circuit. When measured with a 10-megohm DVOM, this may display as low as 350 millivolts. The oxygen sensor signal varies from about 800 millivolts when exhaust is rich to about 50 millivolts when exhaust is lean.

DTC will set if HO2S 1 voltage remains excessively high for an extended period of time.

PCM continuously monitors Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this period, PCM counts the number of times that a rich-to-lean and lean-to-rich response is indicated and adds the amount of time taken to complete all transitions. With this information, an average time for each transition can be determined. If average response time is too slow, DTC will be set.

A lean-to-rich transition is indicated when HO2S voltage changes from less than 300 millivolts to greater than 600 millivolts. A rich-to-lean transition is indicated when HO2S voltage changes from greater than 600 millivolts to less than 300 millivolts. An HO2S that responds too slowly is likely to be faulty and should be replaced.

The PCM supplies a bias voltage of about 450 millivolts between the Heated Oxygen Sensor (HO2S) high signal and low reference circuits. When measured with a 10-megohm DVOM, this may display as low as 350 millivolts. The oxygen sensor signal varies from about 800 millivolts when exhaust is rich, to about 50 millivolts when exhaust is lean.

DTC will set if HO2S 1 voltage remains at or about the 450 millivolts bias for an extended period of time.

Heated Oxygen Sensors (HO2S) are used to minimize amount of time required to enter closed-loop fuel control operation and to allow accurate catalyst monitoring. The HO2S 1 heater voltage is supplied directly from the ignition 1 circuit. HO2S 1 heater control circuit is connected to PCM. PCM controls HO2S heater operation by grounding the control circuit using an internal solid state device called a driver. The primary function of the driver is to supply ground for the component being controlled.

PCM will run the heater test only after a cold start, determined by engine coolant temperature and intake air temperature at time of start-up, and will test only once during an ignition cycle. When engine is started, PCM will monitor HO2S voltage. When HO2S voltage indicates a sufficiently active sensor, PCM determines how much time has elapsed since start-up. The driver for HO2S 1 heater control circuit has the ability to measure amount of current drawn by the controlled device. If PCM determines that too much time was required for the HO2S 2 to become active, DTC will set.

To control 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 which oxidizes the HC and CO present in exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the Heated Oxygen Sensor (HO2S) No. 1 and 2.

The HO2S 1 sensor produces an output signal which indicates amount of oxygen present in the exhaust gas entering the 3-way catalytic converter. The HO2S 2 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst. This indicates the catalyst's ability to efficiently convert the exhaust gases. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than the signal produced by the HO2S 2 sensor. DTC will set if HO2S 2 signal voltage remains excessively low for an extended time.

The PCM supplies a bias voltage of about 450 millivolts between the Heated Oxygen Sensor (HO2S) high signal and low signal circuits. When measured with a 10-megohm DVOM this may display as low as 320 millivolts. The oxygen sensor varies the voltage within a range of about 1000 millivolts when exhaust is rich, down through about 10 millivolts when exhaust is lean. PCM constantly monitors the HO2S signal during closed-loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. DTC will set if HO2S 2 voltage remains excessively high for an extended period of time.

The PCM supplies a bias voltage of about 450 millivolts between the Heated Oxygen Sensor (HO2S) high signal circuit and HO2S low signal circuit. When measured with a 10-megohm DVOM, this may display as low as 350 millivolts. The oxygen sensor signal varies from about 800 millivolts when exhaust is rich, to about 50 millivolts when exhaust is lean

PCM constantly monitors the HO2S signal during closed-loop operation, then compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. If HO2S 2 voltage remains at or about the 450 millivolts bias for an extended period of time, DTC will set.

The PCM supplies a bias voltage of about 450 millivolts between the Heated Oxygen Sensor (HO2S) high signal circuit and HO2S low signal circuit. When measured with a 10-megohm DVOM, this may display as low as 350 millivolts. The oxygen sensor signal varies from about 800 millivolts when exhaust is rich, to about 50 millivolts when exhaust is lean

DTC will set if HO2S 2 voltage remains at or about the 450 millivolts bias for an extended period of time.

Heated Oxygen Sensors (HO2S) are used in order to minimize amount of time required to enter closed-loop fuel control operation and to allow accurate catalyst monitoring. HO2S 1 heater voltage is supplied directly from the ignition 1 circuit. The HO2S 1 heater control circuit is connected to PCM. PCM controls HO2S heater operation by grounding the control circuit using an internal solid state device called a driver. The primary function of the driver is to supply ground for the component being controlled.

PCM will run the heater test only after a cold start (determined by engine coolant temperature and intake air temperature at the time of start-up) and will test only once during an ignition cycle. When engine is started, PCM will monitor HO2S voltage. When HO2S voltage indicates a sufficiently active sensor, PCM determines how much time has elapsed since start-up. DTC will set if PCM determines that too much time was required for HO2S 2 to become active.

The PCM controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during open loop and closed-loop operation. During open loop, PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed-loop, PCM adds oxygen sensor inputs to calculate short and long term fuel trim (fuel delivery adjustments). If oxygen sensors indicate a lean condition, fuel trim values will be greater than zero percent. If oxygen sensors indicate a rich condition, fuel trim values will be less than zero percent. The short term fuel trim values change rapidly in response to Heated Oxygen Sensor (HO2S) voltage signals. The long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. DTC will set if PCM detects an excessively lean condition.

PCM controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during open loop and closed-loop. During open loop, PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During closed-loop, oxygen sensor inputs are added and used by PCM to calculate the short and long term fuel trim (fuel delivery adjustments). If oxygen sensors indicate a lean condition, fuel trim values will be greater than zero percent. If oxygen sensors indicate a rich condition, fuel trim values will be less than zero percent. The short term fuel trim values change rapidly in response to HO2S voltage signals. The long term fuel trim makes coarse adjustments in order to maintain air/fuel ratio of 14.7:1. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the Evaporative Emission (EVAP) canister is causing a rich condition. If PCM detects an excessively rich condition, this DTC will set. If PCM detects excessive vapor, then a pass is logged.

PCM enables appropriate fuel injector on intake stroke for each cylinder. A voltage is supplied directly to fuel injectors. PCM controls each fuel injector by grounding the control circuit via a solid state device called a driver. PCM monitors status of each driver. If PCM detects an incorrect voltage for the commanded state of the driver, a fuel injector control DTC sets.

PCM provides ignition positive voltage to coil side of fuel pump relay. When ignition switch is first turned on, PCM energizes fuel pump relay, which applies power to fuel pump. PCM enables fuel pump relay as long as engine is cranking or running, and crankshaft reference pulses are received. If no crankshaft reference pulses are received, PCM de-energizes fuel pump relay after 2 seconds. PCM monitors voltage on fuel pump relay control circuit. DTC will set if PCM detects an incorrect voltage on fuel pump relay control circuit.

PCM uses information from the Ignition Control (IC) module and Camshaft Position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring the variations in crankshaft rotation speed for each cylinder, PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter to overheat under certain conditions. Malfunction Indicator Light (MIL) will flash on and off when conditions for 3-way catalytic converter overheating are present.

Knock Sensor (KS) module is integrated in PCM. Input signals from KS is used to determine if excessive detonation (knock) is present. If excessive knock is present, PCM will retard timing until knock goes away. When KS module is missing or malfunctioning, PCM will set DTC.

The PCM contains integrated Knock Sensor (KS) diagnostic circuitry. An input signal from KS is used to detect engine detonation, allowing PCM to retard Ignition Control (IC) spark timing based on amplitude and frequency of KS signal being received. The KS produces an AC signal under all engine operating conditions. During engine operation, PCM calculates average voltage of KS signal. If knock sensor system is operating normally, PCM will see KS signal voltage vary at greater than or less than the calculated voltage average. If PCM detects KS input signal equal to the KS average voltage for longer than 95 percent of calibrated time, DTC will set.

The circuit uses 2 different types of Crankshaft Position (CKP) sensors. The 7X CKP sensor "B" is connected directly to Ignition Control (IC) module, and consists of CKP 1 sensor signal circuit and low reference circuit.

The 24X CKP sensor "A" connects directly to the PCM and consists of the 12-volt reference circuit, medium resolution engine speed signal circuit, and the low reference circuit.

During cranking, the Ignition Control (IC) module monitors the 7X crankshaft position sensor signal. Once the IC module determines spark synchronization, 3X reference signals are sent to PCM. PCM will command all 6 injectors on for one priming shot of fuel in all cylinders. After priming, injectors are left off for the next 6 fuel control reference signals (2 crankshaft revolutions). This allows each cylinder a chance to use the fuel from the priming shot. During this waiting period, a cam pulse would have been received by PCM.

PCM uses the Camshaft Position (CMP) sensor signal pulses to initiate sequential fuel injection and constantly monitors the number of pulses on CMP signal circuit, and compares the number of pulses to the number of 24X reference pulses and the number of 3X reference pulses being received. If PCM receives an incorrect number of pulses on CMP reference circuit, DTC will set and PCM will initiate injector sequence without the CMP signal with a one in 6 chance that injector sequence is correct. Engine will continue to start and run normally, although the misfire diagnostic will be affected if a misfiring condition occurs.

PCM tests Exhaust Gas Recirculation (EGR) valve during deceleration by momentarily commanding EGR valve on while monitoring engine MAP. PCM will illuminate MIL and store DTC P0401 if expected increase in MAP is not seen under certain conditions during deceleration.

PCM monitors EGR valve pintle position input to ensure that valve responds properly to commands from PCM. The EGR (linear) 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 voltage or ground circuit, then the ignition positive driver signals PCM to set DTC.

PCM monitors EGR valve pintle position input to ensure that valve responds properly to commands from PCM. PCM compares actual EGR position with desired EGR position when valve is commanded open. If actual EGR position is 15 percent less than desired EGR position when PCM is commanding EGR valve open, DTC will set.

PCM monitors EGR valve pintle position input to ensure that valve responds properly to commands from PCM. PCM compares actual EGR position with desired EGR position when valve is commanded open. If actual EGR position is 15 percent less than desired EGR position when PCM is commanding EGR valve opened, DTC will set.

Secondary Air Injection (AIR) pump is used lower tailpipe emissions on start-up. PCM grounds the AIR pump relay control circuit, which energizes the AIR pump. PCM also grounds the AIR combination valve vacuum control circuit, which energizes the AIR vacuum solenoid valve. Vacuum is then applied to both AIR combination valve diaphragms which open the shutoff valves. PCM enables both circuits simultaneously when AIR system operation is desired. When AIR system is active, the AIR pump forces fresh air into exhaust stream in order to accelerate catalyst operation. The AIR solenoid valves replace the conventional check valves. When AIR system is inactive, the shut-off valves prevent airflow in either direction. DTC will set if an airflow problem is detected.

Ignition voltage is supplied directly to secondary Air Injection (AIR) relay. The PCM supplies ground path to relay control circuit via an internal solid state device called a driver. Each driver has a fault line which is monitored by the PCM. When PCM commands the solenoid on, voltage on control circuit should be low, about zero volts. When PCM commands the solenoid off, voltage on the control circuit should be high, about battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

The PCM will monitor the control circuit for short to ground, short to voltage, open circuit, open solenoid or an internally-shorted or excessively low resistance solenoid.

Ignition voltage is supplied directly to the secondary AIR pump relay. The PCM supplies ground path to relay control circuit via an internal solid state device called a driver. Each driver has a fault line which is monitored by PCM. When PCM commands the relay on, voltage on control circuit should be low (near zero volts). When PCM commands the relay off, voltage on control circuit should be high (near battery voltage). If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

The PCM will monitor the control circuit for a short to ground, short to voltage, open circuit, open relay, or an internally shorted or excessively low resistance relay.

To control 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 which oxidizes the HC and CO present in exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The converter also has the ability to store excess oxygen and release the stored oxygen to promote these reactions. This Oxygen Storage Capacity (OSC) is a measurement of the catalyst's ability to control emissions. The PCM monitors this process using a Heated Oxygen Sensor (HO2S), located in exhaust stream past the 3-way converter. When the catalyst is functioning properly, the HO2S 2 is slow to respond to a large change in the HO2S 1 signal. When HO2S 2 responds quickly to a large change in the HO2S 1 signal, the OSC and efficiency of the catalyst is considered to be bad and MIL will be illuminated if subsequent tests also indicate a failure.

The Evaporative Emission (EVAP) large leak test applies vacuum to EVAP system and monitors vacuum decay. PCM monitors Fuel Tank Pressure (FTP) sensor signal to determine vacuum decay rate. At an appropriate time, PCM turns the EVAP canister purge valve and vent valve are turned on. This allows engine to draw a vacuum on EVAP system. At a calibrated time or vacuum level, the PCM turns the purge valve OFF (closed), sealing the system, and monitors the VTP sensor input in order to determine EVAP system vacuum. DTC will set if system is unable to achieve the calibrated vacuum level or vacuum level decreases too rapidly.

The Evaporative Emission (EVAP) small leak test applies vacuum to the EVAP system and monitors vacuum decay. The PCM monitors the Fuel Tank Pressure (FTP) sensor signal to determine vacuum decay rate. At an appropriate time, the PCM turns the EVAP canister purge valve and vent valve are turned on. This allows engine to draw a vacuum on EVAP system. At a calibrated time or vacuum level, PCM turns purge valve off (closed), sealing the system, and monitors the FTP sensor input in order to determine EVAP system vacuum decay. If system detects a leak larger than a calibrated amount DTC will set.

An ignition voltage is supplied directly to the Evaporative Emission (EVAP) purge solenoid. The EVAP purge solenoid is Pulse Width Modulated (PWM). The PCM controls the EVAP purge solenoid ON time by grounding the control circuit via an internal switch called a driver. The scan tool displays amount of ON time as a percentage. The PCM monitors the status of the driver. If PCM detects an incorrect voltage for the commanded state of the driver, DTC sets.

A restricted or blocked Evaporative Emission (EVAP) vent path is detected by PCM monitoring the fuel tank pressure during normal operation. The PCM commands the EVAP vent solenoid off (open) and EVAP canister purge solenoid on (open). The fuel tank pressure should remain low as vacuum is drawn on EVAP system. If the vent path is blocked or restricted, vacuum level will increase and DTC will set.

A restricted or blocked Evaporative Emission (EVAP) vent path is detected by PCM monitoring the fuel tank pressure during normal operation. The PCM commands the EVAP vent solenoid off (open) and EVAP canister purge solenoid on (open). The fuel tank pressure should remain low as vacuum is drawn on EVAP system. If the vent path is blocked or restricted, vacuum level will increase and DTC will set.

An incorrect Fuel Tank Pressure (FTP) sensor signal is detected by monitoring fuel tank pressure when ignition is first turned on during a cold start. If fuel tank pressure signal is out of range, EVAP diagnostic will not be able to detect leaks. If any of the conditions described are present, DTC will set.

Output Driver Modules (ODMs) are used by PCM in order to turn on many of the current-driven devices that are needed to control various engine and transmission functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which PCM is commanding on. ODMs have the capability of diagnosing each output circuit individually.

The PCM monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative Emission (EVAP) diagnostic. PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as fuel tank pressure decreases (negative pressure or vacuum - high voltage). The FTP sensor signal voltage decreases as fuel tank pressure increases (positive pressure - low voltage). When FTP sensor signal drops to less than a predetermined value, DTC will set.

PCM monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative Emission (EVAP) diagnostic. PCM supplies a 5-volt reference and ground to sensor. The FTP sensor signal voltage increases as fuel tank pressure decreases (negative pressure or vacuum - high voltage). The FTP sensor signal voltage decreases as fuel tank pressure increases (positive pressure - low voltage). DTC will set when FTP sensor signal voltage increases to more than a predetermined value.

The fuel level sensor changes resistance based on fuel level. PCM monitors the signal circuit of the fuel level sensor in order to determine fuel level. When fuel tank is full, sensor resistance is high and PCM senses a high signal voltage. When fuel tank is empty, sensor resistance is low and PCM senses a low signal voltage. PCM uses fuel level sensor signal circuit in order to calculate the total remaining fuel (%) in tank. PCM sends fuel level percent via the class 2 serial data circuit to the IPC in order to control fuel gauge. The fuel level information is also used for misfire and EVAP diagnostics.

Fuel level sensor changes resistance based on fuel level. PCM monitors the signal circuit of the fuel level sensor in order to determine fuel level. When fuel tank is full, sensor resistance is high and PCM senses a high signal voltage. When fuel tank is empty, sensor resistance is low and PCM senses a low signal voltage. PCM uses the signal circuit of the fuel level sensor in order to calculate the total remaining fuel (%) in the tank. PCM sends the fuel level percent via the class 2 serial data circuit to the IPC in order to control the fuel gauge. The fuel level information is also used for misfire and EVAP diagnostics.

Battery voltage is supplied to cooling fan No. 1 relay from COOL FAN 1 Maxifuse(R). The PCM controls cooling fan 1 relay by grounding the low speed cooling fan relay control circuit via an internal solid state device called a driver. The primary function of the driver is to supply ground for the component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage potential of control circuit should be low (about zero volts). When PCM is commanding that the control circuit to a component be turned off, voltage potential of circuit should be high (about battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC will set.

PCM will monitor the control circuit for short to ground, short to voltage, open circuit, open relay coil, internally shorted or excessively low resistance relay coil. When PCM detects any of these conditions, DTC will set and the affected driver will be disabled.

Battery voltage is supplied to the cooling fan relay and cooling fan No. 2 relay from the COOL FAN 2 Maxifuse(R). The PCM controls the relays by grounding the high speed cooling fan relay control circuit via an internal solid state device called a driver. The primary function of the driver is to supply ground for the component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage potential of control circuit should be low (about zero volts). When PCM is commanding that the control circuit to a component be turned off, voltage potential of the circuit should be high (about battery voltage). If fault detection circuit senses a voltage other than what is expected, DTC will set.

PCM will monitor the control circuit for a short to ground, short to voltage or an open circuit. When PCM detects any these conditions, DTC will set and the affected driver will be disabled.

PCM controls idle speed with Idle Air Control (IAC) valve, located on throttle body, to a calculated RPM based on sensor inputs and actual engine RPM. PCM moves IAC valve in or out to vary amount of airflow into intake manifold and thus decrease or increase idle RPM.

PCM commands IAC in counts. A higher count, allows more air to by-pass throttle plate (higher idle).

The Idle Air Control (IAC) valve is located in throttle body and consists of a movable pintle, driven by a gear attached to an electric motor called a stepper motor. The IAC valve motor is a 2-phase bi-polar permanent magnet stepper motor that is capable of highly accurate rotation or movement, every time polarity of a winding is changed. This change in polarity can be seen when observing a test light connected between ground or battery voltage and an IAC valve circuit while PCM is attempting to change engine RPM (test light will flash on or off each time polarity is changed). PCM does not use a physical sensor to determine IAC pintle position, but uses a predicted number of counts, one count represents one change in polarity which equals one step of stepper motor. The PCM counts the steps it has commanded to determine IAC pintle position. PCM uses IAC valve to control engine idle speed. It does this by changing the pintle position in idle air passage of throttle body. This varies the airflow around the throttle plate when throttle is closed.

To determine the desired position of IAC pintle at idle or during deceleration, PCM refers to engine RPM, battery voltage, air temperature, engine coolant temperature, TP sensor angle, engine load, and vehicle speed. When ignition is turned off after an ignition cycle, PCM will first seat the IAC pintle in the air bypass bore and then retract it a predetermined amount of counts to allow proper amount of air to by-pass the throttle plate for engine start-up. This procedure is known as an IAC reset.

PCM monitors the high side refrigerant pressure via the A/C refrigerant pressure sensor. When pressure is high, signal voltage is high. When pressure is low, signal voltage is low. When pressure is high, PCM commands the cooling fans on. When pressure is too high or too low, PCM will not allow the A/C compressor clutch to engage.

PCM monitors system voltage to make sure that voltage stays within the proper range. Damage to components and incorrect data input can occur when voltage is out of range. PCM monitors system voltage over an extended length of time. If PCM detects a system voltage out of an expected range for the calibrated length of time, DTC will set.

This diagnostic test applies to internal microprocessor integrity conditions within the control module. This diagnostic test also addresses if PCM is not programmed. The following DTCs are not applicable to all vehicles: DTC P0601, P0602 and P1683.

PCM uses an Electrically Erasable Programmable Read Only Memory (EEPROM). EEPROM contains program information and calibrations required for engine, transmission, and powertrain diagnostics operation. EEPROM is not replaceable. When PCM is replaced or a calibration update is required, PCM must be programmed using a scan tool or approved Techline(R) equipment. See POWERTRAIN CONTROL MODULE under PROGRAMMING.

PCM uses an Electrically Erasable Programmable Read Only Memory (EEPROM). EEPROM contains program information and calibrations required for engine, transmission, and powertrain diagnostics operation. EEPROM is not replaceable. When PCM is replaced or a calibration update is required, PCM must be programmed using a scan tool or approved Techline(R) equipment. See POWERTRAIN CONTROL MODULE under PROGRAMMING.

PCM uses the generator turn on signal circuit to control the generator. A high-side driver within the PCM allows PCM to turn generator on and off. When generator operation is desired, PCM sends a 5-volt signal to voltage regulator via the generator turn on signal circuit. This causes the voltage regulator to begin controlling generator field circuit. Once generator is enabled by PCM, voltage regulator controls generator output independently of the PCM. Under certain operating conditions, PCM can turn off the generator by turning off the 5-volt signal on the generator turn on signal circuit. The PCM has fault detection circuitry which monitors the state of the generator turn on signal circuit. If fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage regulator also contains fault detection circuitry. If regulator detects a problem, regulator will ground the generator turn on signal circuit, pulling the voltage low, causing PCM to set DTC.

When this DTC sets, PCM sends a class 2 serial data message to the IPC, illuminating the CHARGE indicator light.

Ignition voltage is supplied directly to Malfunction Indicator Light (MIL). PCM controls MIL by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply ground for the component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage of control circuit should be low, about zero volts. When PCM is commanding control circuit to a component off, voltage potential of circuit should be high, about battery voltage. If fault detection circuit senses a voltage other than what is expected, fault line status will change causing DTC to set.

The Torque Converter Clutch (TCC) brake switch indicates brake pedal status to PCM. The TCC brake switch indicates that brake pedal is either applied or released. The normally closed switch supplies battery voltage to PCM. Applying brake pedal opens TCC brake switch, interrupting voltage to PCM. When PCM receives zero volts at TCC brake switch input, PCM turns off the torque converter clutch Pulse Width Modulation (PWM) solenoid.

If PCM detects an open brake switch (indicating pedal applied) during a number of accelerations, DTC will set. DTC P0719 is a Type "C" DTC.

The Torque Converter Clutch (TCC) brake switch indicates brake pedal status to PCM. The TCC brake switch indicates that brake pedal is either applied or released. The normally closed switch supplies battery voltage to PCM. Applying brake pedal opens the TCC brake switch, interrupting voltage to PCM. When PCM receives zero volts at TCC brake switch input, PCM turns off the torque converter clutch Pulse Width Modulation (PWM) solenoid.

If PCM detects a closed TCC brake switch (indicating pedal released) during a number of decelerations, DTC will set. DTC P0724 is a Type "C" DTC.

Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure which gives an indication of engine load. The MAP sensor has a 5-volt reference and signal circuit. PCM supplies 5 volts to MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. MAP sensor provides a signal to PCM on the signal circuit which is relative to the pressure changes in the manifold. With low manifold absolute pressure such as during idle or deceleration, PCM should detect a low MAP sensor signal voltage. With high manifold absolute pressure such as ignition on, with engine off, or wide open throttle, PCM should detect a high MAP sensor signal voltage. Certain models will also use MAP sensor in order to calculate the Barometric (BARO) pressure when ignition is on, with engine off. The BARO reading may also be updated whenever engine is operated at wide open throttle. PCM monitors MAP sensor signal for voltage out of normal range. If PCM detects a MAP sensor signal voltage that is intermittently high, DTC will set.

Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure which gives an indication of engine load. The MAP sensor has a 5-volt reference and signal circuit. PCM supplies 5 volts to MAP sensor on the 5-volt reference circuit and provides a ground on the low reference circuit. MAP sensor provides a signal to PCM on the signal circuit which is relative to the pressure changes in the manifold. With low manifold absolute pressure such as during idle or deceleration, PCM should detect a low MAP sensor signal voltage. With high manifold absolute pressure such as ignition on, with engine off, or wide open throttle, PCM should detect a high MAP sensor signal voltage. Certain vehicle models will also use MAP sensor in order to calculate the Barometric (BARO) pressure when ignition is on, with engine off. The BARO reading may also be updated whenever engine is operated at wide open throttle. PCM monitors MAP sensor signal for voltage out of normal range. If PCM detects a MAP signal voltage that is intermittently low, DTC P1107 will set.

Intake Air Temperature (IAT) sensor is a thermistor which measures the temperature of the air entering the engine. PCM applies 5 volts through a pull-up resistor to IAT sensor. When intake air is cold, sensor resistance is high and PCM will monitor a high signal voltage on IAT signal circuit. If intake air is warm, sensor resistance is lower causing PCM to monitor a lower voltage. DTC will set when PCM detects an intermittently high signal voltage on the intake air temperature sensor signal circuit.

Intake Air Temperature (IAT) sensor is a thermistor which measures temperature of air entering engine. The PCM applies 5 volts through a pull up resistor to IAT sensor. When intake air is cold, sensor resistance is high and PCM will monitor a high signal voltage on IAT signal circuit. If intake air is warm, sensor resistance is lower causing PCM to monitor a lower voltage. DTC will set when PCM detects an intermittently low signal voltage on IAT signal circuit.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of engine coolant. PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively low ECT signal voltage, which is a high temperature indication, this DTC will set.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of engine coolant. PCM supplies 5 volts to ECT signal circuit. When ECT is cold, sensor resistance is high. When ECT increases, sensor resistance drops. With high sensor resistance, PCM detects a high voltage on ECT signal circuit. With lower sensor resistance, PCM detects a lower voltage on ECT signal circuit. If PCM detects an excessively high signal voltage, which is a low temperature indication, this DTC will set.

Throttle Position (TP) sensor measures amount of throttle opening. PCM uses TP sensor information for fuel delivery calculations. TP sensor readings during acceleration are much higher than those during deceleration or idle. DTC will set if PCM senses TP sensor voltage intermittently greater than 4.7 volts with engine running and TP signal voltage is intermittently greater than 4.7 volts.

The Throttle Position (TP) sensor is used by PCM to determine throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with 3 circuits: the 5-volt reference circuit, low reference circuit and signal circuit. Rotation of TP sensor rotor from closed throttle position to Wide Open Throttle (WOT) position provides PCM with a signal voltage from less than one volt to more than 4 volts through the TP sensor signal circuit. If PCM detects an intermittent excessively low signal voltage, this DTC will set.

PCM monitors the Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this test period, PCM counts the number of times that HO2S signal voltage crosses the rich-to-lean and lean-to-rich thresholds. If PCM determines that HO2S did not switch enough times, DTC will be set.

A lean-to-rich switch is determined when HO2S voltage changes from less than 300 millivolts to greater than 600 millivolts. A rich-to-lean switch is determined when HO2S voltage changes from greater than 600 millivolts to less than 300 millivolts.

PCM continuously monitors the Heated Oxygen Sensor (HO2S) activity for 100 seconds. During this period, PCM counts the number of times that HO2S responds from rich-to-lean and from lean-to-rich and adds the amount of time required to complete all the transitions. With this information, an average time for all the transitions can be determined. PCM then divides the rich-to-lean average by the lean-to-rich average to obtain a ratio. If HO2S transition time ratio is not within the appropriate range, DTC is set, indicating that the oxygen sensor is not responding as expected to changes in exhaust oxygen content.

Engine oil pressure switch is a normally closed switch that opens with the proper oil pressure. With ignition on, and engine off, PCM should detect a low signal voltage input. With engine running, pressure switch opens and PCM should detect a high signal voltage input. PCM tests the state of the engine oil pressure circuit with ignition on, and engine off. If PCM detects a high voltage input on engine oil pressure signal circuit, DTC will set.

The Crankshaft Position (CKP) system variation learning feature is used to calculate reference period errors caused by slight tolerance variations in crankshaft, crankshaft balancer interrupter rings, and crankshaft position sensor hall effect switches. The calculated error allows PCM to accurately compensate for reference period variations. The crankshaft position system variation learning feature enhances the ability of the PCM to detect misfire events over a wider range of engine speed and load.

The crankshaft position system variation values are stored in the PCM non-volatile memory after the crankshaft position system variation learn procedure has been performed. DTC indicates that crankshaft position system variation values have not been stored in the PCM and crankshaft position system variation learn procedure must be performed. The learn procedure is required after PCM replacement, engine replacement, crankshaft replacement, crankshaft balancer replacement, CKP sensor replacement, any engine repairs which disturbs crankshaft/harmonic balancer-to-crankshaft position sensor relationship.

Ignition control (IC) module has independent power and ground circuits. The circuits between the IC module and PCM consist of the IC timing signal, IC timing control, low-resolution engine speed signal and low reference signal.

The IC module sends 3X signals to PCM. The IC module controls the timing advance during engine cranking. The timing advance changes to PCM control after PCM receives the second 3X signal and PCM applies 5 volts to the IC timing signal circuit. The timing advance switches to PCM control.

The Ignition Control (IC) module has independent power and ground circuits. The circuits between the IC module and PCM consist of the IC timing signal, IC timing control, low-resolution engine speed signal and low reference signal.

The IC module sends 3X signals to PCM. The IC module controls the timing advance during engine cranking. The timing advance changes to PCM control after PCM receives the second 3X signal and PCM applies 5 volts to IC timing signal circuit. The timing advance switches to PCM control.

The Ignition Control (IC) module has independent power and ground circuits. The circuits between the IC module and PCM consist of the IC timing signal, IC timing control, low-resolution engine speed signal and low reference signal.

The IC module sends 3X signals to PCM. The IC module controls the timing advance during engine cranking. The timing advance changes to PCM control after PCM receives the second 3X signal and PCM applies 5 volts to IC timing signal circuit. The timing advance switches to PCM control.

The Ignition Control (IC) module has independent power and ground circuits. The circuits between the IC module and PCM consist of the IC timing signal, IC timing control, low-resolution engine speed signal and a low reference signal.

The IC module sends 3X signals to PCM. The IC module controls timing advance during engine cranking. The timing advance changes to PCM control after the PCM receives the second 3X signal and PCM applies 5 volts to IC timing signal circuit. The timing advance switches to PCM control.

The 3X reference signal is produced by the Ignition Control (IC) module. The IC module calculates the 3X reference signal by dividing the Crankshaft Position (CKP) sensor 7X pulses by 2 when engine is running and when CKP synchronizing pulses are being received. The PCM uses the 3X reference signal to calculate engine RPM and crankshaft position at engine speeds greater than 1600+/-150 RPM. The PCM also uses these pulses to initiate injector pulses. PCM compares the 3X reference pulses to the 24X CKP pulses and the Camshaft Position (CMP) sensor pulses.

If PCM receives an incorrect number of pulses on the 3X circuit, this DTC will set and PCM will use the 24X CKP reference circuit for fuel and ignition control. The engine will continue to start and run using only the 24X CKP and the camshaft position sensor signals.

PCM receives rough road information from the Electronic Brake Control Module (EBCM) on the serial data circuit. PCM uses this information to enhance the misfire diagnostic by distinguishing crankshaft speed variations caused by driving on rough road surfaces from variations caused by true misfires. EBCM transmits rough road information based on inputs from wheel speed sensors. If EBCM detects a condition which will allow it to properly identify rough road situations while a misfire condition is being detected by the PCM, DTC will set.

PCM receives rough road information from the Electronic Brake Control Module (EBCM) on the class II serial data circuit. PCM detects engine misfire by detecting variations in crankshaft deceleration between firing strokes. For accurate detection of engine misfire, PCM must be able to distinguish between crankshaft deceleration caused by actual misfire or deceleration caused by rough road conditions.

The ABS system can detect if vehicle is on a rough road based on wheel acceleration/deceleration data supplied by the wheel speed sensors. If ABS system detects rough road greater than a predetermined threshold, this information is sent to the PCM via the serial data (UART). PCM can then take the rough road into account when calculating misfire. Even if the ABS is malfunctioning and cannot detect rough roads, the misfire diagnostic will continue to run.

PCM monitors the Exhaust Gas Recirculation (EGR) valve pintle position input in order to ensure that valve responds properly to commands from PCM. When ignition is on, PCM learns the EGR learned minimum position. PCM compares the EGR learned minimum position to EGR position sensor when EGR valve is commanded closed. If EGR position sensor indicates that EGR valve is still open when PCM is commanding EGR valve closed, DTC will set.

This DTC will test for undesired intake manifold vacuum flow to the Evaporative Emission (EVAP) system. The PCM seals the EVAP system by commanding EVAP purge valve off (closed) and EVAP vent valve on (closed). PCM monitors the Fuel Tank Pressure (FTP) sensor to determine if vacuum is being drawn on EVAP system. If vacuum in EVAP system is more than a predetermined value within a predetermined time, DTC will set.

This DTC will test for undesired intake manifold vacuum flow to the Evaporative Emission (EVAP) system. The PCM seals the EVAP system by commanding EVAP purge valve off (closed) and EVAP vent valve on (closed). PCM monitors the Fuel Tank Pressure (FTP) sensor to determine if vacuum is being drawn on EVAP system. If vacuum in EVAP system is more than a predetermined value within a predetermined time, DTC will set.

Ignition voltage is supplied directly to the A/C compressor clutch relay. The PCM controls the relay by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply ground for the component being controlled. Each driver has a fault line which is monitored by PCM. When PCM is commanding a component on, voltage of the control circuit should be near zero volts. When PCM is commanding the control circuit to a component off, voltage potential of circuit should be near battery voltage. If fault detection circuit senses a voltage other than what is expected, DTC will set.

Traction Control System (TCS) uses Anti-Lock Brake System (ABS) in conjunction with PCM fuel and ignition controls to limit drive wheel slippage during acceleration.

DTC will set when desired torque signal Pulse Width Modulation (PWM) is less than 10 percent or greater than 95 percent and condition is present for at least 10 seconds.

The theft deterrent control module produces theft deterrent fuel enable signal when ignition is on and proper transponder key value is detected. The PCM monitors fuel enable signal during crank. If proper signal is present on the class 2 serial data circuit, PCM enables fuel delivery in order to allow engine to start. If PCM determines that fuel enable signal is not present or incorrect while engine is running, the theft deterrent control module will enter a fail enable state. The engine will not stall or stop running. If theft deterrent control module is in fail enable, the PassKey III(tm) system is not active, and engine will start.

The theft deterrent control module produces theft deterrent fuel enable signal when ignition is on and proper transponder key value is detected. The PCM monitors the fuel enable signal during crank. If the proper signal is present on the class 2 serial data circuit, the PCM enables fuel delivery in order to allow engine to start. If PCM is replaced, the replacement PCM should learn the password within a few seconds after ignition is turned on. DTC P1630 is an information code indicating that PCM is ready to learn the theft deterrent password. The engine starts and continues to run with DTC P1630 set.

Theft deterrent control module produces theft deterrent fuel and starter enable signal when ignition is on and proper transponder key value is detected. The PCM monitors fuel and starter enable signal during crank. If proper signal is present on the class 2 serial data circuit, the PCM enables fuel delivery and starter operation in order to allow engine to start. If PCM detects an incorrect password, Vehicle Theft Deterrent (VTD) system failure or attempted vehicle theft, DTC P1631 is set. Engine will not start or crank as long as the condition is present.

PCM monitors 5-volt reference "A" circuit to TP, MAP and EGR position sensors.

PCM monitors 5-volt reference 2 circuit as a sensor feed for the A/C refrigerant pressure sensor. PCM monitors voltage on the 5-volt reference 2 circuit. If voltage is out of tolerance, DTC will set.

PCM monitors 5-volt reference "B" circuit as a sensor feed for the A/C refrigerant pressure sensor and Fuel Tank Pressure (FTP) sensor. PCM monitors voltage on the 5-volt reference "B" circuit. If voltage is out of tolerance, PCM will set DTC P1639.

Output Driver Modules (ODM) are chips located inside PCM. ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to PCM microprocessor. ODM 1 determines if voltage or current may cause damage to PCM. The PCM monitors voltage through the ignition 1 input. Any incorrect current that is on a circuit to the ODM will cause ODM to report this DTC.

Output Driver Modules (ODM) are chips located inside PCM. ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to PCM microprocessor. ODM 2 determines if voltage or current may cause damage to PCM. The PCM monitors voltage through the battery input. Any incorrect current that is on a circuit to the ODM will cause ODM to report this DTC.

Output driver modules (ODM) are chips located inside PCM. ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to PCM microprocessor. ODM 3 determines if voltage or current may cause damage to PCM. The PCM monitors voltage through the battery input. Any incorrect current that is on a circuit to ODM will cause ODM to report this DTC.

Output driver modules (ODM) are chips located inside PCM. ODMs provide grounded outputs that control devices. Each output has an internal feedback circuit that connects to PCM microprocessor. ODM 4 determines if voltage or current may cause damage to PCM. The PCM monitors voltage through the battery input. Any incorrect current that is on a circuit to ODM will cause ODM to report this DTC.

The Electronic Brake Control Module (EBCM) and PCM simultaneously controls the traction control. PCM reduces amount of torque supplied to drive wheels by retarding spark timing and selectively turning off fuel injectors. EBCM actively applies brakes to front wheels in order to reduce torque.

EBCM sends a requested torque message via a Pulse Width Modulated (PWM) signal to PCM. The duty cycle of the signal is used to determine how much engine torque EBCM is requesting PCM to deliver. Normal values are between 10-90 percent duty cycle. The signal should be at 90 percent when traction control is not active and at lower values during traction control activations. PCM supplies a pull-up voltage of 5 volts that EBCM switches to ground to create the signal.

PCM sends a delivered torque message via a PWM signal to EBCM. The duty cycle of signal is used to determine how much engine torque PCM is delivering. Normal values are between 10-90 percent duty cycle. The signal should be at low values (around 10 percent) at idle and higher values under driving conditions. EBCM supplies a pull-up voltage of 12 volts that PCM switches to ground to create the signal.

When certain PCM DTCs are set, PCM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to EBCM indicating that traction control is not allowed.