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Diagnosis & Repair

  1. Connect scan tool to DLC. Turn ignition on. Select CLEAR INFORMATION function. Using scan tool, place vehicle into CHECK MODE. Operate vehicle within FREEZE FRAME conditions. If DTC P0401 resets, go to next step. If DTC P0401 does not reset, check for an intermittent problem. See TESTS W/O CODES article.
  2. Ensure engine is at normal operating temperature. Connect a vacuum gauge to EGR pressure transducer port "Q". Start engine and accelerate to 2500 RPM. If vacuum gauge reads vacuum, go to next step. If gauge does not read vacuum, go to step 12).
  3. Remove vacuum gauge. Using a hand-held vacuum pump, apply vacuum to EGR valve. If engine runs rough or stalls, go to step 5). If engine does not run rough or stall, go to next step.
  4. Remove EGR valve and inspect for sticking pintle, carbon deposits or plugged intake manifold passage. Repair as necessary. If no problems are found, replace EGR valve. Retest system.
  5. Turn ignition on. Disconnect EGR vacuum regulator solenoid harness connector. Using a voltmeter, measure voltage of solenoid power feed circuit. If reading is 10-12 volts, go to next step. If reading is not as specified, go to step 11).
  6. Using an ohmmeter, measure resistance of EGR vacuum regulator solenoid. If resistance is 37-44 ohms, go to next step. If resistance is not as specified, replace EGR vacuum regulator solenoid. Retestsystem.
  7. Using an ohmmeter, check for continuity between outer casing and each terminal of EGR vacuum regulator solenoid. If continuity is present at either terminal, replace EGR vacuum regulator solenoid. Retest system. If continuity is not present at either terminal, go to next step.
  8. Blow air into port "E" of EGR vacuum regulator solenoid. If air passes through port "G" (filter side) of solenoid, go to next step. If air does not pass through as specified, replace EGR vacuum regulator solenoid. Retest system.
  9. Using a fused jumper wire, apply battery voltage to power feed terminal of EGR vacuum regulator solenoid. Connect remaining terminal to ground. Blow air into port "E". If air passes through port "F", go to next step. If air does not pass through as specified, replace EGR vacuum regulator solenoid. Retest system.
  10. Disconnect PCM harness connectors. Check for open or short in EGR vacuum regulator solenoid control circuit (Black/Red wire). Repair as necessary. If wire is okay, replace PCM. Retest system.
  11. Repair open or short in Black/Red wire between engine compartment relay/fuse box and EGR vacuum regulator solenoid. Retestsystem.
  12. Turn ignition off. Remove vacuum hoses "P", "Q" and "R" from pressure transducer. Start engine. Accelerate engine to 2500 RPM. Plug ports "P" and "R". Blow air into port "Q". If strong resistance to airflow is felt, go to next step. If little resistance is felt, go to step 14).
  13. Remove EGR pressure transducer valve. Check exhaust hose for restrictions, splits and cracks. Repair as necessary. If no problems are found, replace EGR pressure transducer. Retest system.
  14. Check vacuum source to EGR pressure transducer for restrictions, splits and cracks. Repair as necessary. If no problems are found, replace EGR pressure transducer. Retest system.
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