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DTC P1491 - EGR System Malfunction

  1. Perform PCM reset procedure. See TESTS W/CODES - INTRODUCTION article. Connect SCS Service Connector (07PAZ-0010100 ). Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral until radiator fan comes on. Road test vehicle for about 10 minutes. Maintain engine speed at 1700-2500 RPM. If DTC P1491 is indicated, go to next step. If DTC P1491 is not indicated, problem is intermittent. System is okay at this time. Check for poor connections or loose wires between EGR valve connector and PCM. See WIRING DIAGRAMS article.
  2. Start engine and allow it to idle. Measure voltage between EGR valve 6-pin harness connector terminals No. 4 (Pink wire) and No. 6 (Black wire). See Fig 1 . See WIRING DIAGRAMS article. If battery voltage does not exist, go to next step. If battery voltage exists, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
  3. Turn ignition off. Disconnect EGR valve 6-pin connector. Using a fused jumper wire, connect battery voltage to EGR valve terminal No. 4 (Pink wire). Start engine and allow it to idle. Using a jumper wire, connect battery ground to EGR valve terminal No. 6 (Black wire). If engine stalls or runs rough, go to next step. If engine does not stall or run rough, replace EGR valve.
  4. Turn ignition off. Disconnect PCM 25-pin connector "B". Check for continuity in Pink wire between PCM 25-pin connector "B" terminal B7 and EGR valve 6-pin connector terminal No. 4. See Figure and Figure . If continuity exists, go to next step. If continuity does not exist, repair open in Pink wire. See WIRING DIAGRAMS article.
  5. Check for continuity in Black wire between ground and EGR valve 6-pin harness connector terminal No. 6. See Fig 1 . If continuity does not exist, repair open in Black wire between EGR valve and ground connection G101 located at end of intake manifold, under Intake Air Temperature (IAT) sensor. See WIRING DIAGRAMS article. If continuity exists, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
    Fig 1: Identifying EGR Valve 6-Pin Connector
    G96G01352Courtesy of AMERICAN HONDA MOTOR CO., INC.
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