DTC P0401: EGR System Failure
NOTE:
EGR system operation is monitored when engine temperature is more than 180°F (82°C), ambient temperature is more than 40°F (4.4°C), engine is in closed loop, oxygen sensor is operating, engine is under steady load with throttle open and oxygen sensor controller is not near its limits. If all conditions are met, the EGR will be turned off and on. Oxygen sensor signal is monitored for changes in output signal during this test. DTC may be stored in Powertrain Control Module (PCM) if all conditions are not met and no significant change or too much change exists. Possible causes are; exhaust leak, restricted intake manifold or EGR backpressure transducer line, defective EGR backpressure transducer, defective EGR valve, improperly installed EGR valve or inadequate vacuum supply to EGR valve.
- Turn ignition on with engine off. Using scan tool, check for DTCs. If GLOBAL GOOD TRIP counter is not displayed and equal to zero, go to next step. If GLOBAL GOOD TRIP counter is displayed and equal to zero, go to step 3 .
- At this time, conditions for EGR system failure does not exist or is an intermittent problem. Using scan tool, read FREEZE FRAME data while attempting to duplicate the condition that caused DTC to be set by paying special attention to the conditions that EGR system operating is monitored. EGR system operation is monitored when engine temperature is more than 180°F (82°C), ambient temperature is more than 40°F (4.4°C), engine is in closed loop, oxygen sensor is operating, engine is under steady load with throttle open and oxygen sensor controller is not near its limits. If EGR system failure reoccurs, go to next step. If EGR system failure does not reoccur, condition no longer exists. Perform TEST VER-5A3 .
- Turn off all accessories. Start engine and warm engine to normal operating temperature. Disconnect vacuum supply hose from EGR solenoid located on top of EGR backpressure transducer. See Fig 1 . Using vacuum gauge, check vacuum on vacuum supply hose for EGR solenoid. If vacuum is more than 10 in. Hg, go to next step. If vacuum is 10 in. Hg or less, repair vacuum supply to EGR solenoid. Perform TEST VER-5A3 .
- Reinstall vacuum supply hose on EGR solenoid. Disconnect vacuum hose from top of EGR valve. See Fig 1 . Connect vacuum gauge on vacuum hose for EGR valve. If vacuum reading pulsates, go to next step. If vacuum reading does not pulsate, go to step 7 .
- Monitor vacuum reading while momentarily increasing engine speed to more than 2000 RPM. If vacuum reading stabilizes, go to next step. If vacuum reading does not stabilize, replace EGR valve assembly. Perform TEST VER-5A3 .
- Remove EGR valve. Inspect EGR valve, intake manifold and signal tube to EGR for restrictions. Signal tube is located below EGR valve. See Fig 1 . If restrictions exist, repair or replace components as necessary. Perform TEST VER-5A3 . If no restrictions exist, replace EGR valve assembly. Perform TEST VER-5A3 .
- Check for sizeable exhaust leaks. If no sizeable exhaust leaks exist, go to next step. If sizeable exhaust leaks exist, repair as necessary. Perform TEST VER-5A3 .
- Reinstall vacuum hose on top of EGR valve. Disconnect backpressure hose from bottom of EGR backpressure transducer. See Fig 1 .
- Install pressure gauge on backpressure hose. If pressure reading does not pulsate, go to next step. If pressure reading pulsates, replace EGR valve assembly. Perform TEST VER-5A3 .
- Check for loose EGR valve mounting bolts or defective EGR valve mounting gasket. If loose EGR valve mounting bolts or defective EGR valve mounting gasket exist, repair as necessary. Perform TEST VER-5A3 . If EGR valve mounting bolts and EGR valve mounting gasket are okay, replace EGR valve assembly. Perform TEST VER-5A3 .