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DTC P0400: Exhaust Gas RECIRCULATION (EGR) Flow Malfunction

  1. Turn ignition on. Wait a few seconds then turn ignition off. EGR stepper motor should operate for 0.6 second after switching ignition off. If operation is as specified, go to step  3 . If operation is not as specified, disconnect EGR valve harness connector and go to next step.
  2. Turn ignition on. Measure voltage between ground and EGR valve harness connector terminals No. 2 and 5 (Red/Black wires). Turn ignition off. Reading should be 10-14 volts. If reading is as specified, go to next step. If reading is not as specified, check Red/Black wires for an open or short. Repair as necessary and retest system.
  3. Turn ignition on. Measure voltage (backprobe) between ground and appropriate terminals at PCM 26-pin harness connector "A". See EGR VOLTAGE SPECIFICATIONS  table. If readings are as specified, go to next step. If readings are not as specified, go to step  5 .
    EGR VOLTAGE SPECIFICATIONS

    Terminal No. Wire Color Volts
    8 Light Green/Red 10-14
    9 Red/Yellow 0-1
    21 Green/White 0-1
    22 Orange/Green 10-14
  4. Check for stuck or faulty EGR valve, or clogged EGR passage. Go to EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING article. Repair as necessary. If EGR system tests as specified, replace PCM and retest system.
  5. Turn ignition off. Connect scan tool to Data Link Connector (DLC). Turn ignition on. Observe engine coolant temperature displayed on scan tool. Proceed with test when ECT value is a minimum of 176°F (80°C). With engine idling and foot off accelerator, open EGR valve by selecting EGR mode in MISC. TEST menu. As EGR opening increases, idle speed should decrease accordingly. If idle drops, go to next step. If idle does not drop, check for clogged EGR passage, stuck or faulty EGR valve, or poor performance of ECT sensor or TP sensor.
  6. Turn ignition off. Check wiring between EGR valve and PCM for an open or short. Check for a poor connection at PCM 26-pin harness connector "A", and at EGR valve. If wiring and connectors are okay, replace PCM and retest system.
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