P0401
SYMPTOM
P0401 EGR SYSTEM PERFORMANCE
WHEN MONITORED
During engine decal, 26 to 4 MPH. Engine Coolant Temp greater than 70 °C (158 °F). Engine run time greater than 120 seconds.
SET CONDITION
The PCM monitors engine roughness. During decal, the EGR is opened and the PCM monitors engine then monitors engine roughness with the valve open. If an increase of engine roughness is not present, an error is detected. Two Trip Fault.
POSSIBLE CAUSES
- (Z958) 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. Scan Tool Testing and Procedures
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>> Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5. Powertrain Verification Test - Ver 5
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 (NGC) POWERTRAIN VERIFICATION TEST VER-5.
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 pint and passage ways.
Obstruction in the EGR tubes.
Were any problem found?
Yes>> Repair or replace the EGR Assembly as necessary. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
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 (NGC) POWERTRAIN VERIFICATION TEST VER-5.
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 (Z958) 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 (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 7
7. (Z958) EGR SOLENOID GROUND CIRCUIT OPEN
Turn the ignition off.
Using a 12-volt test light connected to battery voltage, probe the (Z958) 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 (Z958) EGR Solenoid ground circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
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 (NGC) POWERTRAIN VERIFICATION TEST VER-5.
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 VER-5 - NGC.
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 (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Replace and program the Powertrain Control Module per Service Information. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.