Theory of Operation
The fuel feedback system will maintain a stoiciometric fuel/air mixture,14.7:1, by modifying the injector pulsewidth
according to the oxygen content of the exhaust gas. The PCM makes short termand long term fuel corrections to
maintain stoiciometric fuel/air ratio for best catalytic converter efficiency. Short term fuel correction is based on
upstream O2 sensor output and is designed for quick engine response. The long term fuel correction compensated
for variations in the engine specifications, sensor tolerances and component aging and is designed to correct rich
and lean conditions over a longer period of time.
When Monitored:
With the engine running in closed loop mode, the ambient/battery temperature above 20 deg. F and altitude
below 8500 ft.
Set Condition:
If the PCM multiplies short term compensation by long term adaptive and a purge fuel multiplier and the result
is below a certain value for 30 seconds over two trips, a freeze frame is stored, the MIL illuminates and a
trouble code is stored. Two Trip Fault. Three good trips to turn off the MIL.
Possible Causes
O2 SENSOR
(K41) O2 SENSOR 1/1 SIGNAL CIRCUIT OPEN
(K41) O2 SENSOR 1/1 SIGNAL CIRCUIT SHORTED TO VOLTAGE
1/1 O2 SENSOR HEATER OPERATION
EVAP SYSTEM OPERATION
TP SENSOR VOLTAGE GREATER THAN 0.92 OF A VOLT WITH THROTTLE CLOSED
TP SENSOR
FUEL FILTER/PRESSURE REGULATOR
MAP SENSOR
ECT SENSOR
ENGINE MECHANICAL CONDITION
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.GOOD TRIP EQUAL TO ZERO
NOTE: Check for contaminates that may have damaged the O2 Sensor: contaminated fuel, unapproved sil-
icone, oil and coolant.
Ignition on, engine not running.
With the scan tool, read DTCs and record the related Freeze Frame data.
NOTE: Any O2 Sensor, TPS, ECT, MAP, or EVAP DTCs must be repaired before continuing.
Is the Good Trip Counter displayed and equal to zero?
Ye s>>
Go To 2
No>>
Refer to the INTERMITTENT CONDITIONSymptom (Diagnostic Procedure).
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
2.CHECKING FUEL PRESSURE
Turn the ignition off.
WARNING: The fuel system is under a constant pressure (even with the engineoff). Before testing or ser-
vicing any fuel system hose, fitting or line, the fuel system pressure mustbe released.
Install a fuel pressure gauge.
Ignition on, engine not running.
With the scan tool, actuate the ASD FuelSystem test and observe the fuel pressure gauge.
NOTE: Fuel pressure specification is 379 KPa +/- 14 KPa (55 psi +/- 2 psi).
Choose a conclusion that best matches your fuel pressure reading.
Within Specification
Go To 3
Above Specification
Replace the fuel filter/pressure regulator.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
CAUTION: Stop All Actuations.
3.O2 SENSOR OPERATION
Ignition on, engine not running.
With the scan tool, monitor all of the O2 Sensor voltage readings.
Is the voltage above 4.5 volts for all of the O2 Sensors?
Ye s>>
Go To 4
No>>
Go To 11
4.O2 SENSOR HEATER OPERATION
Turn the ignition off.
NOTE: Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test. Allow
the O2 Sensor voltage to stabilize between 4 and 5 volts.
Ignition on, engine not running.
With the scan tool, actuate the O2 Heater Test.
With the scan tool, monitor O2 Sensor voltage for at least 2 minutes.
Does the voltage stay above 4.5 volts?
Ye s>>
Replace the O2 Sensor that had the voltage reading above 4.5 volts.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 5
5.EVAP SYSTEM OPERATION
NOTE: The engine must be at operating temperature and in closed loop to perform this test.
Start the engine.
WARNING: When the engine is operating, do not stand in a direct line with thefan. Do not put your hands
near the pulleys, belts, or fan. Do not wear loose clothing.
Allow the engine to reach normal operating temperature.
With the scan tool select System Tests, perform the Purge Vapors Test.
Observe the Short Term Adaptive value and press 3 to flow.
NOTE: Short Term Adaptive value change.
Did the Short Term Adaptive value change?
Ye s>>
Go To 6
No>>
Refer to the Driveability category and perform the appropriate Diagnostictest.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
6.TP SENSOR VOLTAGE GREATER THAN 0.92 OF A VOLT WITH THROTTLE CLOSED
Ignition on, engine not running.
With the scan tool, read TP Sensor voltage.
NOTE: The throttle must be against the stop.
Isthevoltage0.92ofavoltorlesswiththeThrottleclosed?
Ye s>>
Go To 7
No>>
Check for a binding throttle condition. If OK, replace the Throttle Position Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
7.TP SENSOR SWEEP
With the scan tool, read the TP Sensor voltage.
While monitoring the scan tool, slowly open and close the throttle.
Does the voltage increase and decrease smoothly?
Ye s>>
Go To 8
No>>
ReplacetheThrottlePositionSensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
8.MAP SENSOR OPERATION
Turn the ignition off.
Connect a Vacuum Gauge to a Manifold Vacuum source.
Start the engine.
Allow the engine to idle.
NOTE: If engine will not idle, maintain a constant RPM above idle.
With the scan tool in Sensors, read the MAP Sensor vacuum value.
Is the scan tool reading within 1
of the Vacuum Gauge reading?
Ye s>>
Go To 9
No>>
Replace the MAP Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
NOTE: Remove the vacuum gauge before continuing.
9.ECT SENSOR OPERATION
NOTE: For this test to be valid, the thermostat must be operating correctly.
NOTE: This test works best if performed on a cold engine (cold soak)
Ignition on, engine not running.
With the scan tool, read the Engine Coolant Temperature Sensor value. If theenginewasallowedtositovernight
(cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature.
NOTE: If engine coolant temperature is above 82°C (180°F), allow the engine to cool until 65°C (150°F) is
reached.
Start the Engine.
During engine warm-up, monitor the Engine Coolant Temperature value. Thetemp value change should be a
smooth transition from start up to normal operating temp 82°C (180°F). Thevalue should reach at least 82°C
(180°F).
Did the Engine Coolant Temperature value increase smoothly and reach at least 82°C?
Ye s>>
Go To 10
No>>
Replace the Engine Coolant Temperature Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
10.ENGINE MECHANICAL PROBLEM
Check for any of the following conditions/mechanical problems.
AIR INDUCTION SYSTEM - must be free from restrictions.
ENGINE VACUUM - must be at least 13 inches in neutral
ENGINE VALVE TIMING - must be within specifications
ENGINE COMPRESSION - must be within specifications
ENGINE EXHAUST SYSTEM - must be free of any restrictions or leaks.
ENGINE PCV SYSTEM - must flow freely
TORQUE CONVERTER STALL SPEED - must be within specifications
POWER BRAKE BOOSTER - no internal vacuum leaks
FUEL - must be free of contamination
FUEL INJECTOR - plugged or restricted injector; control wire not connectedtocorrectinjector
Are there any engine mechanical problems?
Ye s>>
Repair as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
11 .O2 SENSOR
Disconnect the sensor harness connector of the O2 Sensor(s) that had a voltage value greater than 4.5 volts in the
previous step.
Ignition on, engine not running.
With the scan tool, monitor the O2 Sensor voltage reading(s).
Is the O2 Sensor voltage above 4.5 volts?
Ye s>>
Replace the O2 Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 12
12.(K41) O2 SENSOR 1/1 SIGNAL CIRCUIT OPEN
Turn the ignition off.
Disconnect the PCM harness connectors.
Measure the resistance of the (K41) O2 Sensor 1/1 Signal circuit from
the PCM harness connector to the O2 Sensor harness connector.
Is the resistance below 5.0 ohms?
Ye s>>
Go To 13
No>>
Repair the open in the (K41) O2 Sensor 1/1 Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
13.(K41) O2 SENSOR 1/1 SIGNAL CIRCUIT SHORTED TO VOLTAGE
Ignition on, engine not running.
Leave the O2 Sensor and PCM harness connectors disconnected.
Measure the voltage on the (K41) O2 Sensor 1/1 Signal circuit at the
1/1 O2 Sensor harness connector.
Is the voltage above 5.2 volts?
Ye s>>
Repair the short to voltage in the O2 Sensor Signal circuit.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 14
NOTE: Turn the ignition off before continuing.
14.PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal
push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and
Ground circuits.
If there are no possible causes remaining, view repair.
Repair
Replace and program the Powertrain Control Module per Service Information.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
Theory of Operation
The fuel feedback system will maintain a stoiciometric fuel/air mixture,14.7:1, by modifying the injector pulsewidth
according to the oxygen content of the exhaust gas. The PCM makes short termand long term fuel corrections to
maintain stoiciometric fuel/air ratio for best catalytic converter efficiency. Short term fuel correction is based on
upstream O2 sensor output and is designed for quick engine response. The long term fuel correction compensated
for variations in the engine specifications, sensor tolerances and component aging and is designed to correct rich
and lean conditions over a longer period of time.
When Monitored:
With the engine running in closed loop mode, the ambient/battery temperature above 20 deg. F and altitude
below 8500 ft.
Set Condition:
If the PCM multiplies short term compensation by long term adaptive and a certain percentage is exceeded for
two trips, a freeze frame is stored, the MIL illuminates and a trouble code is stored. Two Trip Fault. Three good
trips to turn off the MIL.
Possible Causes
FUEL PRESSURE OUT OF SPECS
RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
O2 SENSOR
(K43) O2 SENSOR 2/1 SIGNAL CIRCUIT SHORTED TO GROUND
O2 SENSOR 2/1 HEATER OPERATION
TP SENSOR
MAP SENSOR
ECT SENSOR
ENGINE MECHANICAL CONDITION
FUEL FILTER/PRESSURE REGULATOR
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING).
Diagnostic Test
1.GOOD TRIP EQUAL TO ZERO
NOTE: Check for contaminates that may have damaged the O2 Sensor: contaminated fuel, unapproved sil-
icone, oil and coolant.
Ignition on, engine not running.
With the scan tool, read DTCs and record the related Freeze Frame data.
Is the Good Trip Counter displayed and equal to zero?
Ye s>>
Go To 2
No>>
Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
5.FUEL PUMP MODULE
If there are no possible causes remaining, view repair.
Repair
Replace the Fuel Pump Module.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
6.O2 SENSOR OPERATION
Turn the ignition off.
NOTE: Wait a minimum of 10 minutes to allow the O2 Sensor and Exhaust System to cool down before
continuing the test.
Ignition on, engine not running.
With the scan tool, monitor all of the O2 Sensor voltage readings.
Is the voltage above 4.5 volts?
Ye s>>
Go To 7
No>>
Go To 13
7.O2 SENSOR HEATER OPERATION
Turn the ignition off.
NOTE: Wait a minimum of 10 minutes to allow the O2 Sensor to cool down before continuing the test.
Ignition on, engine not running.
With the scan tool, actuate the 1/1 O2 Heater Test.
With the scan tool, monitor all O2 Sensor voltage readings for at least 2 minutes.
Does the voltage stay above 4.5 volts for any of the O2 Sensors?
Ye s>>
Replace the O2 Sensor that had the voltage reading above 4.5 volts.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 8
8.TP SENSOR VOLTAGE GREATER THAN 0.92 OF A VOLT WITH THROTTLE CLOSED
With the scan tool, read TP Sensor voltage.
NOTE: The throttle must be against the stop.
Isthevoltage0.92ofavoltorlesswiththeThrottleclosed?
Ye s>>
Go To 9
No>>
Check for a binding throttle condition. If OK, replace the Throttle Position Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
9.TP SENSOR SWEEP
With the scan tool, read the TP Sensor voltage.
While monitoring the scan tool, slowly open and close the throttle.
Does the voltage increase and decrease smoothly?
Ye s>>
Go To 10
No>>
ReplacetheThrottlePositionSensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
10.MAP SENSOR OPERATION
Turn the ignition off.
Connect a Vacuum Gauge to a Manifold Vacuum source.
Start the engine.
Allow the engine to idle.
NOTE: If engine will not idle, maintain a constant RPM above idle.
With the scan tool in Sensors, read the MAP Sensor vacuum value.
Is the scan toolreading within 1
of the Vacuum Gauge reading?
Ye s>>
Go To 11
No>>
Replace the MAP Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
NOTE: Remove the vacuum gauge before continuing.
11 .ECT SENSOR OPERATION
NOTE: For this test to be valid, the thermostat must be operating correctly.
NOTE: This test works best if performed on a cold engine (cold soak)
Ignition on, engine not running.
With the scan tool, read the Engine Coolant Temperature Sensor value. If theenginewasallowedtositovernight
(cold soak), the temperature value should be a sensible value that is somewhere close to the ambient temperature.
NOTE: If engine coolant temperature is above 82°C (180°F), allow the engine to cool until 65°C (150°F) is
reached.
Start the Engine.
During engine warm-up, monitor the Engine Coolant Temperature value. Thetemp value change should be a
smooth transition from start up to normal operating temp 82°C (180°F). Thevalue should reach at least 82°C
(180°F).
Did the Engine Coolant Temperature increase smoothly and did it reach at least 82°C (180°F)?
Ye s>>
Go To 12
No>>
Replace the Engine Coolant Temperature Sensor.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)