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DTC P0400: Exhaust Gas RECIRCULATION (EGR) Flow Malfunction

NOTE: Before performing diagnostic tests, clear diagnostic codes and road test vehicle. Drive between 35-40 mph for 7 minutes or more. Increase speed to 60-70 mph, then release gas pedal and allow engine to slow vehicle while coasting to a stop. Recheck for DTC P0400. If code has returned, continue with test procedure.
  1. If DTC P0403 is present, go to DTC P0403: EXHAUST GAS RECIRCULATION (EGR) CIRCUIT MALFUNCTION  . If DTC P0403 is not present, go to next step.
  2. If scan tool is available, go to step  3 . If scan tool is not available, go to step  4 .
  3. Test operation of EGR valve. See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING article. If EGR valve operation is as specified, go to next step. If EGR valve operation is not as specified, go to step  5 .
  4. Inspect operation of manifold differential pressure sensor (MDP). See MANIFOLD DIFFERENTIAL PRESSURE (MDP) SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article. If MDP sensor operation is not as specified, replace sensor and retest system. If MDP sensor operation is as specified, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
  5. Disconnect EGR valve electrical connector. Turn ignition on. Using DVOM, check voltage at EGR harness connector terminals No. 2 and 5 (both Blue/Black wires). If 10-14 volts are present at both wires, go to next step. If voltage is not present at both wires, repair open or short circuit in Blue/Black wires between main relay and EGR valve.
  6. Turn ignition off. Reconnect EGR valve electrical connector. Unplug PCM electrical connectors. See PIN VOLTAGE/CIRCUIT RESISTANCE CHARTS article for PCM connector and terminal identification. Using DVOM, measure resistance between PCM harness connector terminal C51-3-4 (Blue/Black wire) and the following PCM harness connector terminals:
    • C51-2-13 (Light Green/Red wire).
    • C51-2-14 (Light Green/Yellow wire).
    • C51-2-15 (Light Green/White wire).
    • C51-2-16 (Light Green wire).

    Resistance on each circuit should be between 20-24 ohms. If resistance values are as specified, go to next step. If resistance values are not as specified, repair open or short circuit in appropriate wire and retest system.

  7. Check for plugged EGR passage. Repair as necessary. If passage is not plugged, problem is due to intermittent malfunction or faulty PCM. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. If unable to duplicate intermittent problems, replace PCM and retest system.
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