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DTC P0401: EGR System Failure: Testing

NOTE: EGR solenoid is integral to EGR valve. If EGR solenoid is defective, EGR valve must be replaced.
  1. Turn ignition on. Using scan tool, read DTCs. If GOOD TRIP counter is displayed and equal to zero, go to next step. If GOOD TRIP counter is not displayed and equal to zero, go to step  13 .
    NOTE: In the following step, if engine is running rough at idle before EGR system test actuated, go to step  3 .
  2. Turn ignition on. Turn all accessories off. Start engine and warm to normal operating temperature. Using scan tool, select ENGINE SYSTEM TEST, then EGR SYSTEM TEST. Select FLOW on scan tool. If engine runs rough or stalls, go to next step. If engine does not run rough or stall, go to step  8 .
  3. Turn ignition off. Disconnect EGR solenoid harness connector. EGR solenoid is integral to EGR valve. EGR valve is mounted to rear of right cylinder head. Start engine and let it idle. If engine does not idle rough or stall, go to next step. If engine idles rough or stalls, inspect EGR tube assembly. Repair or replace EGR tube assembly as necessary. If EGR tube assembly is okay, replace EGR valve.
  4. Turn ignition off. Disconnect PCM harness connectors. See Figure . Measure resistance between ground and EGR solenoid control circuit (Gray/Yellow wire) at EGR solenoid harness connector terminal No. 4. See Fig 1 . If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair short to ground in Gray/Yellow wire.
  5. Measure resistance between EGR solenoid control circuit (Gray/Yellow wire) at EGR solenoid harness connector terminal No. 4 and sensor ground circuit (Black/Light Blue wire) at EGR solenoid harness connector terminal No. 3. If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair short between EGR solenoid control circuit and sensor ground circuit.
  6. Inspect EGR assembly for the following:
    • Gasket(s) for leaking.
    • Damage or holes in EGR tubes.
    • Carbon build-up on or near EGR pintle and passage ways.
    • Obstruction in EGR tubes.

    If a problem is found, repair as necessary. If no problems are found, go to next step.

  7. If no other possible causes are remaining, PCM is assumed to be defective. Replace PCM.
  8. Turn ignition off then on. Ensure all accessories are turned off. Disconnect EGR solenoid harness connector. Connect a test light between ASD relay output circuit (Orange/Dark Green wire) at EGR solenoid harness connector terminal No. 6 and EGR solenoid control circuit (Gray/Yellow wire)at EGR solenoid harness connector terminal No. 4. See Fig 1 . Using scan tool, actuate EGR solenoid. If test light flashes on and off, inspect EGR tubes for obstructions and damage. Repair as necessary. If EGR tubes are okay, replace EGR solenoid assembly. If test light does not flash on and off, go to next step.
  9. Turn ignition off then on. Using scan tool, actuate ASD relay. Using a test light connected to ground, probe ASD relay output circuit (Orange/Dark Green wire) at EGR solenoid harness connector terminal No. 6. If test light illuminates, go to next step. If test light does not illuminate, repair open in ASD relay output circuit. See WIRING DIAGRAMS article.
  10. Turn ignition off then on. Measure voltage between ground and EGR solenoid control circuit (Gray/Yellow wire) at EGR solenoid harness connector terminal No. 4. If voltage is one volt or less, go to next step. If voltage is more than one volt, repair short to voltage in Gray/Yellow wire between PCM and EGR solenoid.
  11. Turn ignition off. Disconnect PCM harness connectors. See Figure . Measure resistance of EGR solenoid control circuit (Gray/Yellow wire) between EGR solenoid harness connector terminal No. 4 and terminal No. 40 at PCM C1 harness connector. See Figure and Fig 1 . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Gray/Yellow wire.
  12. If no other possible causes are remaining, PCM is assumed to be defective. Replace PCM.
  13. Conditions that set DTC are not present at this time. Perform the following to help identify intermittent condition:
    • With engine running at normal operating temperature, wiggle related wiring harness while monitoring related parameters on scan tool. If voltage changes or DTC sets while wiggling wiring harness, repair connectors or wiring harness where wiggling caused voltage to change or DTC to set.
    • Review freeze frame information on scan tool. Duplicate conditions present when DTC was set.
    • Refer to any technical service bulletins that may apply.
    • Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires.
    • Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals.

    If a problem is found, repair as necessary. If no problems are found, test is complete.

Fig 1: Identifying EGR Solenoid Harness Connector Terminals
G98C00168Courtesy of DAIMLERCHRYSLER CORPORATION
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