P0401
P0401-EGR SYSTEM PERFORMANCE
For a complete wiring diagram refer to: Electrical Diagrams
When Monitored
Engine running for greater than two minutes with the Engine Coolant Temp greater than 70°C (158°F). EGR active. Less than 8500 feet. Ambient temperature greater than -6°C (20°F).
Set Condition
The PCM closes the EGR valve while monitoring the O2 Sensor signal. Once a closed EGR fueling sample has been established the PCM then ramps in EGR and additional fueling while monitoring the O2 sensor signal in the open state. A fueling sample is again established. The PCM then compares the different O2 Sensor signal readings (fueling samples). If a larger than expected variation is detected, a soft failure is recorded. Three soft failures set a one trip failure. After two failed trips, a DTC is set and the MIL is illuminated.
Possible Causes
- (Z904) EGR SOLENOID GROUND CIRCUIT OPEN
- (K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO GROUND
- (K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO BATTERY VOLTAGE
- (K35) EGR SOLENOID CONTROL CIRCUIT OPEN
- EGR SOLENOID ASSEMBLY
- PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. ACTIVE DTC
Ignition on, engine not running.
With a scan tool, read DTCs.
Is the DTC active at this time?
Yes >> Go To 2
No >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. EGR OPERATION
NOTE: If the vehicle is running rough at idle (scan tool not actuating) follow the yes path to continue.
Turn all accessories off.
Start the engine.
Allow the engine to reach normal operating temperature.
With the scan tool, enter Engine System Test, then EGR System Test.
Actuate the FLOW function in the EGR System Test.
Did the engine run rough or stall?
Yes >> Go To 3
No >> Go To 6
3. EGR VALVE OPEN AT IDLE
Turn the ignition off.
Disconnect the EGR Solenoid Assembly harness connector.
Start engine. Attempt to allow the engine to idle.
Does the engine run rough or stall?
Yes >> Inspect the EGR tube assembly If OK, replace the EGR valve.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 4
4. EGR VALVE ASSEMBLY INSPECTION
Inspect the EGR Assembly for the following.
Gasket(s) for leaking
Damage and/or holes in the EGR tube(s)
Carbon build up on or near the EGR pintle and passage ways. Obstruction in the EGR tubes.
Were any problem found?
Yes >> Repair or replace the EGR Assembly as necessary.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 5
5. (K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO BATTERY VOLTAGE
Turn the ignition off.
Disconnect the EGR Solenoid harness connector.
Ignition on, engine not running.
Measure the voltage on the (K35) EGR Solenoid Control circuit in the EGR Solenoid connector.
Is the voltage above 1.0 volt?
Yes >> Repair the short to battery voltage in the (K35) EGR Solenoid Control circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 10
6. EGR SOLENOID ASSEMBLY
Disconnect the EGR Solenoid harness connector.
Using a 12-volt test light, jump across the (K35) EGR Solenoid Control terminal and the (Z904 Ground terminal in the EGR Solenoid harness connector.
With the scan tool, actuate the EGR solenoid.
Does the 12-volt test light flash on and off?
Yes >> Inspect the tube(s) for obstructions and damage, repair as necessary If OK, replace the EGR Solenoid Assembly.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 7
7. (Z904) EGR SOLENOID GROUND CIRCUIT OPEN
Turn the ignition off.
Using a 12-volt test light connected to battery voltage, probe the (Z904) EGR Solenoid ground circuit in the EGR Solenoid harness connector.
Does the 12-volt test light illuminate brightly?
Yes >> Go To 8
No >> Repair the open in the (Z904) EGR Solenoid ground circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
8. (K35) EGR SOLENOID CONTROL CIRCUIT SHORTED TO GROUND
Disconnect the PCM harness connector.
Measure the resistance between ground and the (K35) EGR Solenoid Control circuit in the EGR Solenoid harness connector.
Is the resistance below 100 ohms?
Yes >> Repair the short to ground in the (K35) EGR Solenoid Control circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 9
9. (K35) EGR SOLENOID CONTROL CIRCUIT OPEN
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
Measure the resistance of the (K35) EGR Solenoid Control circuit from the EGR Solenoid harness connector to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes >> Go To 10
No >> Repair the open in the (K35) EGR Solenoid Control circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
10. 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.
Were there any problems found?
Yes >> Repair as necessary
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Replace and program the Powertrain Control Module per Service Information.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test