Engine Controls - Tests W/codes: Diagnosis Pontiac Bonneville IX

SELF-DIAGNOSTIC SYSTEM

Note. Powertrain Control Module (PCM) may also be referred to as Electronic Control Module (ECM) in some diagnostic charts and figures. Terms are used interchangeably.

Control module is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, control module will store a numerical code and, in most cases, illuminate SERVICE ENGINE SOON light located on instrument panel. SERVICE ENGINE SOON light is also referred to as the Malfunction Indicator Light (MIL). Malfunctions are recorded as hard failures or as intermittent failures.

Note. Models equipped with OBD II diagnostic systems may have additional diagnostic information and procedures available; however, to fully utilize information and procedures requires the use of a Tech 1 scan tester. See tester owners manual for additional information.

DIAGNOSTIC PROCEDURE

Diagnosis of computerized engine control system should be performed in following order

1. Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See «BASIC TESTING»(ref-19935) article in this section.
2. If trouble codes were displayed, determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See «HARD OR INTERMITTENT TROUBLE CODE DETERMINATION»(ref-19847-S32485317822001010200000) . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in «TESTS W/O CODES»(ref-19937) article in this section.
3. If no trouble codes are present and a driveability problem exists, refer to SYMPTOMS in «TESTS W/O CODES»(ref-19937) article in this section. Doing so will help identify proper system or component to check in «SYSTEM/COMPONENT TESTS»(ref-19889) article in this section.
4. After necessary repairs are made, clear trouble codes, verify vehicle will enter "closed loop" operation and ensure code does not reset.

Note. For specific information on retrieving codes using a scan tester, refer to user and reference manuals supplied with tester.

Note. Field service mode check can only be performed on vehicles equipped with 12-pin DLC with a wire present in test terminal "B".

DATA LINK CONNECTOR (DLC) TEST TERMINALS (16 PIN)

Scheme 70

READING TROUBLE CODES

Control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Trouble codes may be read by counting flashes of SERVICE ENGINE SOON light (some models) or by reading digital display on a scan tester. Scan tester is faster to use, more accurate and capable of reading information which otherwise would necessitate testing individual control module and sensor/solenoid connector terminals using a digital voltmeter. See SCAN TESTER USAGE and SCAN DATA .

Note. When using most scan testers, a time delay exists between serial data updates. For instantaneous response, a digital voltmeter must be used.

TROUBLE CODE DEFINITION

TROUBLE CODE CONVERSION

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION

During any diagnostic procedure, determine if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes

1. Enter diagnostic mode. Read and record all stored trouble codes. Exit diagnostic mode, and clear trouble codes. See «CLEARING TROUBLE CODES»(ref-19847-S35765130472001010200000) .
2. Apply parking brake, and place transmission in Neutral or Park. Block drive wheels, and start engine. SERVICE ENGINE SOON light should go out. Run warm engine at specified curb idle for 2 minutes and note SERVICE ENGINE SOON light.
3. If SERVICE ENGINE SOON light comes on, enter diagnostic mode. Read and record trouble codes. This will reveal hard failure codes. Oxygen sensor related codes may require a road test to reset hard failure after trouble codes were cleared.
4. If SERVICE ENGINE SOON light does not come on, all stored trouble codes were intermittent failures, except as noted above.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of that sensor or switch for 5 seconds; others require operation for 5 minutes or longer at normal operating temperature, vehicle speed and load. Therefore, some codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate conditions under which code will set.

CLEARING TROUBLE CODES

To clear trouble codes from memory, either to determine if malfunction will occur again or after making necessary repairs, disconnect power supply to PCM for at least 30 seconds or clear codes using a scan tester with code clearing capability.

Diagnostic Aids

Diagnostic aids (located in many trouble code charts) are additional tips used to help diagnose trouble codes when inspected circuit is okay. Diagnostic aids may help lead to a definitive solution to trouble code problem.

SPECIAL TOOLS (DIAGNOSTIC)

Note. A scan tester plugged into DLC may be used to read trouble codes and check voltages in system on serial data line. On most models scan tester is REQUIRED to retrieve vehicle information. For additional information, see SCAN TESTER USAGE and SCAN DATA .

Computerized engine control system is most easily diagnosed using scan tester; however, other tools may aid in diagnosing problems if a scan tester is unavailable. These tools are a tachometer, test light, ohmmeter, digital voltmeter with a 10-megohm input impedance (minimum), vacuum pump, vacuum gauge, fuel injector test lights and 6 jumper wires 6" long (one wire with female connectors at both ends, one wire with male connectors at both ends and 4 wires with male and female connectors at opposite ends). A test light, rather than a voltmeter, must be used when indicated by a diagnostic chart. In addition, special jumper harnesses or testers may be required by manufacturer to facilitate diagnosis.

Circuit Description

Mass Airflow (MAF) sensor measures flow of air which passes through it in a given time. PCM uses this information to monitor operating condition of engine for fuel delivery calculations. A large quantity of air movement indicates acceleration, while a small quantity indicates deceleration or idle. MAF sensor produces a frequency signal, which cannot be easily measured. Diagnose sensor using procedures on this chart.

An intermittent may be caused by a poor connection, mis-routed harness, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection At PCM pin

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

1. Mis-Routed Harness

Inspect MAF sensor harness to ensure it is not too close to high voltage wires, such as spark plug wires.

1. Damaged Harness

Inspect harness for damage. If harness appears okay, observe scan tester while moving related connectors and wiring harness. A change in display would indicate intermittent fault location.

1. Plugged Air Intake Filter

A wide-open throttle acceleration from a stop should cause MAF reading on scan tester to range from about 4-7 grams per second at idle to 100 or greater at time of 1-2 shift. If not, check for restriction.

Intake Air Temperature (IAT) sensor is a thermistor. PCM applies and monitors a 5-volt reference signal to sensor. When air is cold, sensor resistance is high and PCM will measure a high signal voltage. If air is warm, sensor resistance is low causing PCM to measure low voltage.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

1. Intermittent Test

Observe IAT on scan tester while moving related connectors and wiring harness with warm engine running. If failure is induced, IAT display will change to a -40°C temperature reading. This may assist in isolating location of malfunction.

Intake Air Temperature (IAT) sensor is a thermistor. PCM applies and monitors a 5-volt reference signal to sensor. When air is cold, sensor resistance is high and PCM will measure a high signal voltage. If air is warm, sensor resistance is low causing PCM to measure low voltage.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness for short to ground in IAT signal circuit, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

1. Intermittent Test

Observe IAT on scan tester while moving related connectors and wiring harness with warm engine running. If failure is induced, IAT display will change to a reading of about 147°C. This may assist in isolating location of malfunction.

ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors a 5-volt reference signal to sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant increases, sensor resistance becomes less and PCM voltage drops.

Tech 1 displays engine temperature in degrees celsius (°C). After engine is started, temperature should rise steadily to about 90°C, then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

1. Intermittent Test

Using scan tester, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

1. Shifted Sensor

See TEMPERATURE-TO-RESISTANCE VALUES table to test ECT sensor at various temperature levels to evaluate possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.

1. A faulty connection, or an open in sensor circuits will cause Code P0117 to set.

TEMPERATURE-TO-RESISTANCE VALUES (1)

ECT sensor uses a thermistor to control signal voltage to PCM. PCM applies and monitors a 5-volt reference signal to sensor. When engine coolant is cold, sensor (thermistor) resistance is high and PCM will sense a high signal voltage. As engine coolant warms, sensor resistance becomes less and PCM voltage drops. With Code P0118 set, PCM will turn cooling fans on and use a default engine coolant temperature value based on run time.

Tech 1 displays engine temperature in degrees celsius (°C). After engine is started, temperature should rise steadily to about 90°C, then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check the following for

1. A short to ground in coolant sensor signal circuit.
2. Intermittent Test

Using scan tester, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

1. Shifted Sensor

See TEMPERATURE-TO-RESISTANCE VALUES table to test ECT sensor at various temperature levels to evaluate possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.

TEMPERATURE-TO-RESISTANCE VALUES (1)

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from about .20-.74 volt at idle to greater than 4 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by PCM for fuel control and for most of PCM control outputs.

Scan tester displays throttle position in volts. Voltage should increase steadily as throttle is moved toward WOT. An open or short to ground in reference and signal circuits will cause Code P0122 to set. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

1. Intermittent Test

Monitor TP sensor voltage display on scan tester while moving related connectors and wiring harness. If failure is induced,display will change. This may assist in isolating location of malfunction.

1. TP Sensor Scaling

Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TP sensor voltage when throttle is closed (about .20-.74 volt) to greater than 4 volts when throttle is held at WOT position.

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from .20-.74 volt at idle to about 5 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by PCM for fuel control and for most of PCM control outputs.

Scan tester displays throttle position in volts. With closed throttle, ignition on, or at idle, voltage should be about .20-.74 volt. If voltage is not as specified, replace TP sensor. An open in sensor ground circuit will cause Codes P0112, P0712, P0117 and P0123 to set. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

1. Intermittent Test

Monitor TP sensor voltage display on scan tester while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

1. TP Sensor Scaling

Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TP sensor voltage when throttle is closed (about .20-.74 volt) to greater than 4 volts when throttle is held at WOT position.

PCM supplies and monitors a voltage of about .45 volt between PCM sensor low reference circuit and sensor signal circuit. If read with a 10-megohm DVOM, voltage may read as low as .32 volt. Sensor varies voltage within a range of about 1.0 volt (rich) to .10 volt (lean). Sensor is like an open circuit and produces no voltage when less than about 600°F (316°C). Open loop operation is caused by Codes P0131 or P0132, an open sensor circuit, or a cold sensor.

Using scan tester, observe LT fuel trim values at different RPM and air flow conditions. Tech 1 also displays fuel trim cells allowing LT fuel trim values to be checked in each cell, determining when Code P0131 may have been set. LT fuel trim values will be around 158 or greater if conditions exist for Code P0131 to set.

1. Heated Oxygen Sensor Wire

Sensor pigtail may be mispositioned and contacting exhaust manifold.

1. Check for intermittent ground in wire between connector and sensor.
2. Poor PCM to engine block ground.
3. MAF Sensor

System will go lean when MAF sensor output causes PCM to sense a lower than normal airflow. Disconnect MAF sensor. If lean condition no longer exists, replace MAF sensor.

1. Lean Injectors

Perform injector balance test.

1. Fuel Contamination

Water near in-tank fuel pump inlet causing fuel contamination in fuel delivered to injectors. Water causes a lean exhaust and can set Code P0131.

1. Fuel Pressure

If pressure is too low, system will be lean. To confirm, monitor fuel pressure while driving at various speeds and/or load conditions.

1. Exhaust Leaks

If an exhaust leak above oxygen sensor is present, outside air may be allowed to be pulled into exhaust stream and flow past sensor.

1. Vacuum Or Crankcase Leak

Can cause a lean condition and/or possibly a high idle.

1. If all above components/systems are okay, heated oxygen sensor is faulty.
2. Faulty sensor heater or heater circuit

Refer to DIAGNOSTICS AIDS in Code P0134 chart.

PCM supplies and monitors a voltage of about .45 volt between PCM sensor low reference circuit and sensor signal circuit. If read with a 10-megohm DVOM, voltage may read as low as .32 volt. Sensor varies voltage within a range of about 1.0 volt (rich) to .10 volt (lean). Sensor is like an open circuit and produces no voltage when less than about 600°F (316°C). Open loop operation is caused by Codes P0131, P0132 or P0134, or a cold sensor.

1. Fuel Pressure

If pressure is too high, system will be rich. PCM can compensate for some increase; however, Code P0132 will set if pressure gets too high.

1. Rich Injectors Perform injector balance test.
2. Leaking Injectors Check for fuel contaminated oil.
3. EVAP Canister Purge

Check for fuel saturation. If full of fuel, check canister control and hoses.

1. MAF Sensor

System will go rich when MAF sensor output causes PCM to sense a higher than normal airflow. Disconnecting MAF sensor will allow PCM to set a fixed value for sensor. If rich condition no longer exists, replace MAF sensor.

1. Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
2. TP Sensor

An intermittent TP sensor output will cause system to go rich due to a false indication of throttle movement.

1. False rich indication due to silicone contamination of heated oxygen sensor. This will be indicated by Code P0131 accompanied by lean driveability conditions and a powdery White deposit on sensor.
2. Heated Oxygen Sensor (HO2S)

If sensor is internally shorted, sensor voltage displayed on Tech 1 will be greater than one volt. Disconnect sensor with ignition on and engine running. If displayed voltage decreases from greater than 1.0 volt to about .45 volt, replace sensor.

1. Faulty Sensor Heater Or Heater Circuit

See DIAGNOSTICS AIDS in Code P0134 chart.

PCM supplies and monitors voltage of about .45 volt between PCM sensor low reference circuit (Tan wire) and sensor signal circuit (Purple wire). If read with a 10-megohm DVOM, voltage may read as low as .32 volt. Sensor varies voltage within a range of about one volt (rich) to .10 volt (lean). Sensor is like an open circuit and produces no voltage when less than about 600°F (316°C). Open loop operation is caused by open oxygen sensor circuit or a cold sensor.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

1. Faulty Sensor Heater Or Heater Circuit

With ignition on and engine off, sensor voltage displayed on Tech 1 should gradually decrease to less than .25 volt, indicating heater is functioning properly. If display does not read as specified, disconnect sensor and connect test light between terminals "C" and "D". If test light does not light, repair open in suspect wire. If test light lights, replace sensor.

1. Intermittent Test

Using scan tester, monitor sensor signal voltage while moving related connectors and wiring harness with engine running at part throttle in closed loop. If failure is induced, sensor signal voltage reading will change from normal fluctuating voltage (greater than .6 volt and less than .30 volt) to a fixed value of about .45 volt. This may assist in isolating location of malfunction.

A closed loop air/fuel metering system is used to provide best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. Scan tester monitors fuel trim values, and will indicate a change made to fuel delivery by long and short term fuel trim values.

Ideal fuel trim values are about 128. If oxygen sensor signal indicates a lean condition, PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating that PCM is reducing amount of fuel delivered. PCM will set Code P0171 if an excessively lean condition is detected.

Preliminary Inspection

1. Check exhaust for corrosion, loose or missing components.
2. Ensure oxygen sensor is installed properly and pigtail is not contacting hot exhaust or ignition wires.
3. Check vacuum hoses for splits, kinks and proper routing and connections.
4. Check for vacuum leaks at throttle body, intake manifold and EGR valve.
5. Check for proper operation of IAC system.
6. Check proper operation of PCV system.
7. Check throttle body inlet screen for damage and/or foreign objects.
8. Check fuel for excessive water, alcohol, or other contaminates.
9. Ensure PCM and sensor grounds are clean and tight. NOTE: To complete a trip cycle for fuel trim diagnostic, fuel trim diagnostic test must be enabled and run according to conditions required to set Code P0171. A trip is not considered complete until fuel trim diagnostics have been run by PCM.

If problem can not be isolated using diagnostic charts, monitor LT fuel trim and fuel trim cell while operating vehicle under various loads. This may isolate condition which caused Code P0171 to set.

A condition that causes Code P0300 (MISFIRE DETECTED) may also set Code P0171. An extremely lean condition which sets Code P0171 can cause a misfire at idle and Code P0300 to set. If cause of Code P0171 can not be determined and Code P0300 is also set, refer to Code P0300 chart.

A closed loop air/fuel metering system is used to provide best possible combination of driveability, fuel economy and emission control. While in closed loop, PCM monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. Scan tester monitors fuel trim values, and will indicate a change made to fuel delivery by long and short term fuel trim values.

Ideal fuel trim values are about 128. If oxygen sensor signal indicates a lean condition, PCM will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating PCM is reducing amount of fuel delivered. PCM will set Code P0172 if an excessively rich condition is detected.

1. Ensure air intake duct is not collapsed or restricted and air filter is not plugged.
2. Check for damaged or partially plugged throttle body inlet screen.
3. Check for proper operation of IAC system.
4. Check fuel pressure regulator operation, ensuring diaphragm is not ruptured.
5. Check for proper operation and mounting of throttle position sensor. NOTE: To complete a trip cycle for fuel trim diagnostic, fuel trim diagnostic test must be enabled and run according to conditions required to set Code P0172. A trip is not considered complete until fuel trim diagnostic has been run by PCM.

If problem can not be isolated using diagnostic charts, monitor LT fuel trim and fuel trim cell while operating vehicle under various loads. This may isolate condition which caused Code P0172 to set.

PCM uses spark reference signal circuit to improve ignition timing accuracy during crank and at engine speeds up to 1200 RPM. Spark reference circuit allows use of ignition control mode at speeds less than 400 RPM, eliminating need to utilize module mode during start-up, and also allows PCM to calculate true crankshaft position in 1/6 the time that use of fuel control reference signal would permit.

During normal operation, PCM uses spark reference signal to control ignition timing until engine speed exceeds 1200 RPM, at which time fuel control reference signal circuit is used.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside insulation. Check for

1. Backed out connector terminals or broken down insulation.
2. If connections and harness are okay, monitor voltage on spark reference circuit using DVOM while moving related wiring harness and connectors with engine idling. This may assist in isolating any malfunctions.

Knock sensor is used to detect engine detonation and allow PCM to retard Ignition Control (IC) timing based on signal being received. Circuitry within knock sensor causes PCM's supplied 5 volts signal to be pulled down, so that under a no knock condition circuit would measure about 2.5 volts DC. Knock sensor produces an AC signal which rides on 2.5 volts DC voltage. Amplitude and signal frequency is dependent upon knock level.

If circuit becomes open or shorted to ground, voltage will either become greater than 3.5 volts or less than 1.5 volts respectively.

Check signal circuit for a intermittent open or short to ground. Also check for proper installation of PROM. If knock sensor circuit is routed too close to secondary ignition wires, it may induce a voltage and cause a false knock signal.

Knock sensor is used to detect engine detonation and allow PCM to retard Ignition Control (IC) timing based on signal being received. Circuitry within knock sensor causes PCM's supplied 5 volts signal to be pulled down, so that under a no knock condition circuit would measure about 2.5 volts DC. Knock sensor produces an AC signal which rides on 2.5 volts DC voltage. Amplitude and signal frequency is dependent upon knock level.

If circuit becomes open or shorted to ground, voltage will either become greater than 3.5 volts or less than 1.5 volts respectively.

Check signal circuit for a intermittent open or short to ground. Also check for proper installation of PROM. If knock sensor circuit is routed too close to secondary ignition wires, it may induce a voltage and cause a false knock signal.

During cranking, Ignition Control Module (ICM) monitors crankshaft position sensor signal. Signal is used to determine correct cylinder pair to spark first. ICM processes signal then sends a fuel control reference pulse to PCM. When PCM receives this pulse, all 6 injectors will be commanded to open for one priming shot of fuel in all cylinders. After priming, injectors remain off for the next 6 fuel control reference pulses from ICM (2 crankshaft revolutions). This allows each cylinder a chance to use fuel from priming shot.

During this waiting period, a cam pulse will have been received by PCM. PCM will now begin to operate injectors sequentially based on true camshaft position. With engine running, PCM monitors cam and fuel control references pulses received and expects to detect 6 fuel control pulses for each cam pulse.

Code P0341 indicates an intermittent fault and may not set immediately or under all conditions. Customer comments of symptom experienced may assist in isolating cause of condition. A poor connection of fault in camshaft position sensor circuits, or a faulty camshaft position sensor, may cause PCM to reinitialize injector sequence when fault occurs, causing a possible stumble or miss.

A poor connection or fault in fuel control circuit, crankshaft position sensor circuits, 18X portion of crankshaft position sensor, or damaged vanes on harmonic balancer interrupter rings will cause PCM to stop pulsing injectors when fault occurs, causing an intermittent stumble or stall.

During cranking, Ignition Control Module (ICM) monitors crankshaft position sensor signal. Signal is used to determine correct cylinder pair to spark first. ICM processes signal then sends a fuel control reference pulse to PCM. When PCM receives this pulse, all 6 injectors will be commanded to open for one priming shot of fuel in all cylinders. After priming, injectors remain off for the next 6 fuel control reference pulses from ICM (2 crankshaft revolutions). This allows each cylinder a chance to use fuel from priming shot.

During this waiting period, a cam pulse will have been received by PCM. PCM will now begin to operate injectors sequentially based on true camshaft position. However, if cam signal is not present at start-up, Code P0342 will set and PCM will start sequential fuel delivery in random pattern with a one in 6 chance that fuel delivery is correct.

Code P0342 will set when engine is running and cam signal is not received by PCM for last 5 seconds.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out cam signal circuit terminal, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

1. Intermittent Test

If connections and harness are okay, monitor a DVOM connected between PCM cam signal circuit terminal and ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change. This may assist in isolating location of malfunction.

PCM tests exhaust gas recirculation valve by momentarily commanding valve on while monitoring engine RPM. PCM will illuminate Malfunction Indicator Light (MIL) and store Code P0401 if expected drop is not seen for a calibrated number of tests.

An intermittent may be caused by a broken wire inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out EGR control circuit terminal, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

1. Intermittent Test

If connections and harness are okay, monitor a DVOM connected between PCM EGR control circuit terminal and ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

Note. Check exhaust system for blockage (possibly a plugged converter) if EGR valve shows signs of excessive heat. Repair cause of restricted exhaust system as necessary. Injector stuck open may be due to stuck injector pintle, grounded driver circuit or possible faulty PCM. If conditions are not present, oil should be checked for possible fuel contamination.

Vehicle Speed Sensor (VSS) in transaxle provides vehicle speed information to PCM. Voltage level and number of pulses increase with vehicle speed. PCM converts pulsing voltage to MPH, and MPH can be displayed using a scan tester.

Function of VSS buffer, used in past models, has been incorporated into PCM. PCM supplies necessary signal for instrument cluster (4004 pulses per mile) for operating speedometer and odometer.

When vehicle speed is greater than about 3 MPH, Tech 1 should indicate a vehicle speed. Code P0502 indicates an intermittent and may not set immediately or under all conditions. Check sensor circuits for proper connections. Ensure they are clean and tight and harness is correctly routed.

PCM monitors status of TCC brake switch input.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

1. Intermittent Test

Monitor scan tester while moving related connectors and wiring harness. If failure is induced, scan data will change from released to applied, or applied to released. This may assist in isolating location of malfunction.

Transmission range switch is part of Transmission Mounted Neutral Start Switch (TMNSS) mounted on transaxle assembly. Transmission range switch is a multi-signal switch that sends information, relative to gear selector position, to PCM. PRNDL input consists of 4 discrete circuits to pull 4 PCM voltages low in various combinations to indicate each gear range. Voltage level of each of circuits is represented as low equals grounded circuit and high equals open circuit. The 4 states displayed represent decoder parity, "A", "B"and "C" respectively.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

1. Intermittent Test

Monitor scan tester while moving related connectors and wiring harness. If failure is induced, scan data will change from low to high, or high to low. This may assist in isolating location of malfunction.

Transaxle temperature sensor uses a thermistor to vary signal voltage to PCM according to temperature. PCM applies and monitors a 5-volt reference signal to sensor. When transaxle fluid is cold sensor resistance is high. Thus, PCM will monitor a high signal voltage. As transaxle fluid warms, sensor resistance becomes less and voltage drops. At normal operating temperature of 68-194°F (20-90°C) transaxle temperature signal will measure about 2-4 volts.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

1. Intermittent Test

Monitor scan tester while moving related connectors and wiring harness. If failure is induced, scan data will change from low to high, or high to low. This may assist in isolating malfunction.

1. Shifted Sensor

See TEMPERATURE-TO-RESISTANCE VALUES table to test sensor at various temperature levels to evaluate possibility of a shifted sensor which may result in driveability complaints.

1. A faulty connection, or an open in sensor circuits will cause Code P0117 to set.

TEMPERATURE-TO-RESISTANCE VALUES (1)

Transaxle temperature sensor uses a thermistor to vary signal voltage to PCM according to temperature. PCM applies and monitors a 5-volt reference signal to sensor. When transaxle fluid is cold sensor resistance is high. Thus, PCM will monitor a high signal voltage. As transaxle fluid warms, sensor resistance becomes less and voltage drops. At normal operating temperature of 68-194°F (20-90°C) transaxle temperature signal will measure about 2-4 volts.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

1. Intermittent Test

Monitor scan tester while moving related connectors and wiring harness. If failure is induced, scan data will change from low to high, or high to low. This may assist in isolating malfunction.

1. Shifted Sensor

See TEMPERATURE-TO-RESISTANCE VALUES table to test sensor at various temperature levels to evaluate possibility of a shifted (mis-scaled) sensor which may result in driveability complaints.

TEMPERATURE-TO-RESISTANCE VALUES (1)

The Torque Converter Clutch (TCC) eliminates loss of power to torque converter when cruise control is engaged. This allows convenience of automatic and fuel economy of a manual transaxle. The main components of system are 2 PCM controlled solenoids located inside transaxle.

TCC is applied when TCC apply solenoid coil is activated (on) resulting in a straight through mechanical coupling from engine to wheels. TCC is released when TCC apply solenoid coil is deactivated (off) allowing torque converter to operate in conventional manner (fluid coupling between engine and transaxle). TCC PWM solenoid is used to vary hydraulic pressure to converter clutch regulator valve, allowing a smoother engagement of converter clutch.

Scan tester only indicates when PCM has commanded TCC driver on, this does not confirm that TCC is actually engaged. Road test vehicle to determine if TCC is properly functioning. Engine RPM should decrease when tester indicates TCC has been turned on. If diagnosis indicates all electrical circuits and components are okay, check for hydraulic and mechanical problems.

The 4T60E is an electronically shifted transaxle. Within transaxle are 4 solenoids for shift and TCC control. Solenoid "A" is energized for 1st and 4th gear operation. Solenoid "B" is energized for 1st gear as well as 2nd gear operations. The other 2 solenoids are for TCC operation. This diagnostic chart deals with shift control solenoids only.

When ignition is on, both solenoids "A" and "B" receive 12 volts. PCM will ground "A" and "B" circuits for 1st gear until a shift to 2nd gear is commanded. When vehicle speed and TP sensor reach calibrated values, PCM will turn off ground for solenoid "A" and 2nd gear is engaged. Further increase in vehicle speed will cause PCM to turn off ground for solenoid "B", engaging 3rd gear. In 3rd gear, both solenoids are de-energized. In 4th gear, only solenoid "A" is energized.

All PRNDL indications are ignored as far as transaxle shifting is concerned except for manual low gear. If PRNDL inputs indicate manual low has been selected, PCM will keep both solenoids "A" and "B" energized until about 5400 RPM, when PCM will force a shift by de-energizing solenoid "A". Manual 2nd and manual 3rd are controlled hydraulically within transaxle.

PCM controls and monitors injector driver circuits. If any injector feed or control circuit malfunctions, code will set.

An intermittent may be caused by rubbed through wire insulation. Check for

1. Boost control driver circuit shorted to ground.

Intermittent Test

Disconnect PCM Blue connector and install a DVOM to monitor voltage between PCM harness boost control driver circuit terminal and ground. With ignition on, observe voltage while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

Under most conditions, PCM commands boost control solenoid to operate at a 100 percent duty cycle (on) to allow full intake boost pressure upon demand. However, if reverse gear is selected, PCM detects rapid deceleration or engine load is extremely high, reduced boost is desired. Under these conditions, PCM commands boost control solenoid to operate at a zero percent duty cycle (off), which opens by-pass valve to reduce boost pressure by recirculating it back through supercharger inlet.

An intermittent may be caused by rubbed through wire insulation. Check for

1. Boost control driver circuit shorted to ground.

Disconnect PCM Blue connector and install a DVOM to monitor voltage between PCM harness boost control driver circuit terminal and ground. With ignition on, observe voltage while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

When engine is cranking, Ignition Control Module (ICM) sends a spark reference and a fuel control signal to PCM. At start of crank, ICM controls ignition timing (module mode). PCM sends a 5-volt signal on by-pass circuit to switch timing to PCM control when second fuel control pulse is recognized by PCM. Code P1350 will set at start-up if an open is present in ignition control circuit. Code P1361 will set if an open in Ignition Control (IC) circuit, or an open or grounded by-pass circuit is present during time when engine is started. Engine may be started but will run on module mode timing.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

1. Intermittent Test

Monitor a DVOM connected between affected terminal and ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

PCM constantly monitors linear EGR valve pintle position sensor to ensure valve is responding properly to commands from PCM.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

1. Intermittent Test

If connections and harness are okay, monitor a DVOM connected between affected terminal and ground while moving related connectors and wiring harness. If failure is induced, voltage reading will change.

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connections or damaged harness.

Perform intermittent check by monitoring circuit and code status while wiggling related wiring and connectors. If failure is induced, monitored circuit status will change rapidly and/or related code will set.

A/C head pressure switch opens at 200-220 psi. When head pressure switch interrupts ground at PCM, left fan should run at high speed.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

PCM controlled cruise control system is designed to be self-monitored to ensure desired cruise servo position and actual cruise servo position are equal to one another.

Code P1558 may set if cruise control throttle cable binds or intermittently sticks. Outside interference such as a CB antenna lead near PCM wiring harness may induce a false SPS signal and set Code P1558.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Cruise switch within turn signal lever receives ignition voltage from a 15-amp fuse to turn signal lever cruise switches. Cruise ON/OFF, SET/COAST and RESUME/ACCEL switches are inputs to cruise portion of PCM.

Cruise servo vent and vacuum solenoids output are controlled by high side drivers in PCM. When ignition is on, PCM looks at these output lines and will set codes if an incorrect status is seen on any line.

Vent solenoid is a normally-open (de-energized) solenoid valve that allows vacuum in cruise servo to be depleted. When solenoid is on (energized), cruise servo holds vacuum allowing servo to remain retracted and hold throttle open.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection and damaged harness.

Cruise switch within turn signal lever receives ignition voltage from a 15-amp fuse to turn signal lever cruise switches. Cruise ON/OFF, SET/COAST and RESUME/ACCEL switches are inputs to cruise portion of PCM.

Cruise servo vent and vacuum solenoids output are controlled by high side drivers in PCM. When ignition is on, PCM looks at these output lines and will set codes if an incorrect status is seen on any line.

Vacuum solenoid is a normally closed solenoid valve that blocks flow of vacuum to cruise servo. When solenoid is on (energized), solenoid valve opens allowing vacuum to be drawn into servo.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

PCM applies and monitors 5 volts to cruise control servo position sensor through PCM servo position sensor terminal and receives a returned frequency from servo terminal "B" on same circuit. Depending on actual servo position, AC frequency will vary indicating to PCM position of servo blade. PCM uses this information to control servo position when cruise is engaged.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

Power is supplied to cruise control switches and cruise brake switch as well as other circuits by ignition switch. Circuit is protected by a 15-amp fuse.

Note. A short to ground in cruise ON/OFF circuit, SET/COAST, cruise/brake or RESUME/ACCELL will cause a failure of cruise engagement switch. It will not blow 15-amp fuse.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

PCM controlled cruise control system is designed to be self monitored to ensure desired cruise servo position and actual cruise servo position are equal to one another. When Code P1568 is set, vehicle may operate in power management mode and Code P1599 will set. While in power management, PCM will shut off fuel to 3 cylinders to avoid over-revving engine in case throttle is being held open by a sticking cruise control throttle cable, brake vacuum release valve, or cruise control servo. Power management may be perceived as a severe engine miss or lack of power.

Most solenoids leak a small amount of vacuum when closed; however, they should not leak enough to allow servo to reach WOT in 15 seconds with vent closed. When vacuum solenoid is forced on, vacuum will vent to atmosphere unless vent valve is stuck closed.

Code P1568 may set if cruise control throttle cable binds or intermittently sticks. Code P1568 can also be set by manually compressing cruise servo to raise engine speed. Outside interference such as a CB antenna lead near PCM wiring harness may induce a false SPS signal and set Code P1568.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

Traction control system uses anti-lock brake system in conjunction with PCM fuel and ignition controls to limit drive wheel slippage during acceleration. PCM controlled portion of traction control system reduces engine torque by any or all of following methods.

1. Retarding spark advance.
2. Altering air/fuel ratio.
3. Altering boost duty cycle (VIN 1 only).
4. Shutting off up to 3 injectors.

To determine amount of torque reduction required, PCM monitors desired torque PWM signal circuit from Electronic Brake and Traction Control Module (EBTCM). PCM also provides a delivered torque PWM signal, informing EBTCM how much torque is being produced by engine. Code P1571 will set when the following condition is present.

1. If desired torque signal PWM duty cycle is less than 5 percent or greater than 95 percent. Code P1571 will set indicating a problem with desired torque input on circuit.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness for an open or short to ground in desired torque circuit, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

1. Intermittent Test

Using a DVOM observe voltage between PCM desired torque terminal and ground while moving related connectors and wiring harness with warm engine running. If failure is induced, voltage reading will change. This may assist in isolating location of malfunction.

PCM uses serial data line to communicate with various other components and systems within vehicle. If PCM does not receive data from Electronic Brake and Traction Control Module (EBTCM), PCM will store Code P1573 indicating loss of communication with ABS/TCS system.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

1. Poor Connection Or Damaged Harness

Inspect wiring harness for an open or short to ground in serial data circuit, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

1. Intermittent Test

Observe ABS data on Tech 1 while moving related connectors and wiring harness. If failure is induced, Tech 1 data will stop updating. This may assist in isolating location of malfunction.

PCM controlled cruise control system is designed to be self monitored to ensure desired cruise servo position and actual cruise servo position are equal to one another. If actual servo position is too high, PCM will set Code P1568, and vehicle will operate in power management mode. While in power management, PCM will shut off fuel to 3 cylinders to avoid over-revving engine in case throttle is being held open by a sticking cruise control throttle cable, brake vacuum release valve, or cruise control servo. Code P1599 is an information code included to alert service that vehicle has operated in power management mode.

Most solenoids leak a small amount of vacuum when closed; however, they should not leak enough to allow servo to reach WOT in 15 seconds with vent closed. When vacuum solenoid is forced on, vacuum will vent to atmosphere unless vent valve is stuck closed.

A cruise control throttle cable which binds or intermittently sticks may cause vehicle to operate in power management and Code P1599 to set. Code P1599 can also be set by manually compressing cruise servo to raise engine speed.

Outside interference such as a CB antenna lead near PCM wiring harness may induce a false SPS signal and set Code P1599.

To determine engine oil life remaining, PCM monitors engine coolant temperature, number of crankshaft revolutions, vehicle speed, engine speed, and calculated oil temperature. When PCM determines engine oil is near end of its useful life, it will command instrument cluster via serial data circuit to illuminate CHANGE OIL SOON indicator or CHANGE OIL SOON/NOW message after start-up. PCM will command CHANGE OIL SOON indicator or CHANGE OIL SOON/NOW message on after each start-up until engine oil life monitor is reset by grounding oil life monitor reset input circuit through oil life monitor reset switch for more than 5 seconds.

An intermittent Code P1626 or P1629 and/or a possible no-start may be caused by the following.

1. Loss Of Power Or Ground To Theft Deterrent Module

A loose ground or poor ignition or battery condition could cause an intermittent loss of PASS-Key II fuel enable signal and Codes P1626 and P1629 to be set.

1. Dirty, Damaged, Or Loose Connections Or Damaged Harness -Check for any damage to harness which could cause an intermittent open or short to ground, backed out terminals at PCM and theft deterrent module connectors, broken locks, improperly formed or damaged terminals.

PCM monitors system voltage on PCM ignition feed terminal.

An intermittent may be caused by a poor connection, rubbed through wire insulation, a wire broken inside insulation or poor PCM grounds. Check for

1. Poor Connection Or Damaged Harness

Inspect PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connection and damaged harness.

1. Intermittent Test

Using scan tester, monitor system volts display while moving related connectors and wiring harness. If failure is induced, display will abruptly change. This may assist in isolating location of malfunction. An engine stall while manipulating harness indicates PCM has lost voltage at ignition feed terminal (Pink wire). Check for loose connectors in power feed circuit.

Note. Charging with a battery charger while starting engine may set Code P1630.

PCM is used to control several components as shown in wiring schematic. PCM controls these devises through use of a Quad-Driver Module (QDM). When PCM is commanding a component on, voltage potential of output circuit will be low (near zero volt). When PCM is commanding output circuit to a component off, voltage potential of circuit will be high (near battery voltage). Primary function of QDM is to supply ground for component being controlled.

Each QDM has a fault line which is monitored by PCM. Fault line signal is available on data stream for scan tool test equipment display on Tech 1. PCM will compare voltage at QDM based on accepted values of fault line. If QDM No. 1 fault detection circuit senses a voltage other than accepted value, fault line will go from a low signal on data stream to a high signal and Code P1640 will set.

Monitor voltage at each QDM terminal while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may assist in isolating an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If code reoccurs with no apparent connector problem, replace PCM.

PCM is used to control several components as shown in wiring schematic. PCM controls these devices through use of a Quad-Driver Module (QDM). When PCM is commanding a component on, voltage potential of output circuit will be low (near zero volt). When PCM is commanding output circuit to a component off, voltage potential of circuit will be high (near battery voltage). Primary function of QDM is to supply ground for component being controlled.

Each QDM has a fault line which is monitored by PCM. Fault line signal is available on data stream for scan tool test equipment display on Tech 1. PCM will compare voltage at QDM based on accepted values of fault line. If QDM No. 2 fault detection circuit senses a voltage other than accepted value, fault line will go from a low signal on data stream to a high signal and Code P1650 will set.

Monitor voltage at each terminal shown above while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may assist in isolating an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If code reoccurs with no apparent connector problem, replace PCM.

PCM is used to control several components as shown in wiring schematic. PCM controls these devises through use of a Quad-Driver Module (QDM). When PCM is commanding a component on, voltage potential of output circuit will be low (near zero volt). When PCM is commanding output circuit to a component off, voltage potential of circuit will be high (near battery voltage). Primary function of QDM is to supply ground for component being controlled.

Each QDM has a fault line which is monitored by PCM. Fault line signal is available on data stream for scan tool test equipment display on Tech 1. PCM will compare voltage at QDM based on accepted values of fault line. If QDM No. 4 fault detection circuit senses a voltage other than accepted value, fault line will go from a low signal on data stream to a high signal and Code P1670 will set.

Monitor voltage at each terminal shown above while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may assist in isolating an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If code reoccurs with no apparent connector problem, replace PCM.

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connections or damaged harness.

Perform intermittent check by monitoring circuit and code status while wiggling related wiring and connectors. If failure is induced, monitored circuit status will change rapidly and/or related code will set.