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DTC P0401: EGR System Performance: Testing

  1. Turn ignition on, engine not running. With the DRBIII®, read DTCs and record the related Freeze Frame data. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  12.
    2. NOTE: If the engine is running rough at idle (DRBIII® not actuated), go to next step.
  2. Start the engine. Turn all accessories off. Allow the engine to reach operating temperature. With the DRBIII®, enter Engine System Test, then EGR System Test. Actuate the Flow function in the EGR System Test. Does the engine run rough or stall? If yes, go to next step. If no, go to step  7.
  3. Turn the ignition off. Disconnect the EGR Solenoid harness connector. Start engine. Attempt to allow the engine to idle. Does the engine run rough or stall? If yes, inspect the EGR tube assembly and repair as necessary. If EGR tube assembly is okay, replace the EGR valve. If no, go to next step.
  4. Inspect the EGR assembly for leaking gaskets, damage, obstructions and/or holes in the EGR tube(s) and for carbon build-up on or near the EGR pintle and passageway. Were any problems found? If yes, repair or replace the EGR assembly as necessary. If no, go to next step.
  5. Ensure EGR Solenoid is disconnected. Turn ignition on, engine not running. Measure the voltage on the EGR Solenoid Control circuit at the EGR Solenoid harness connector. Is the voltage above 1.0 volt? If yes, repair the short to voltage in the EGR Solenoid Control circuit. If no, go to next step.
    6. NOTE: Before continuing, check the PCM harness connectors for corrosion, damage or terminal push out. Repair as necessary.
  6. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
  7. Turn the ignition off. Using a 12-volt test light connected to ground, probe the EGR Solenoid Control circuit at the EGR Solenoid harness connector. With the DRBIII®, actuate the EGR Solenoid. Does the test light flash on and off? If yes, inspect the EGR tube(s) for damage and obstructions. Repair EGR tube(s) as necessary. If EGR tube(s) are okay, replace EGR Solenoid assembly. If no, go to next step.
  8. Using a 12-volt test light connected to battery voltage, probe the EGR Solenoid Ground circuit in the EGR Solenoid harness connector. Does the 12-volt test light illuminate brightly? If yes, go to next step. If no, repair the open in the EGR Solenoid ground circuit.
  9. Ensure the ignition is off. Disconnect the PCM harness connectors. Measure the resistance between ground and the EGR Solenoid Control circuit at the EGR Solenoid harness connector. Is the resistance below 100 ohms? If yes, repair the short to ground in the EGR Solenoid Control circuit. If no, go to next step.
    10. 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. Use Miller Special Tool (8815) when performing diagnosis at PCM harness connectors.
  10. Measure the resistance of the EGR Solenoid Control circuit from the EGR Solenoid harness connector to the appropriate terminal at Miller Special Tool. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the EGR Solenoid Control circuit.
    11. NOTE: Before continuing, check the PCM harness connectors for corrosion, damage or terminal push out. Repair as necessary.
  11. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
    12. WARNING: When the engine is operating, do not stand in a direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing.
  12. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set. Review the DRBIII® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. Refer to any Technical Service Bulletins (TSB) that may apply. Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals. Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.
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