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DTC P1491: EGR Valve Lift Insufficient Detected

  1. Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING CODES  under SELF-DIAGNOSTIC SYSTEM. Connect SCS Service Connector (07PAZ-0010100) to 2-pin service check connector located under passenger side of instrument panel. See Figure. Start engine and hold engine speed at 3000 RPM, with no load and transmission in Park or Neutral, until cooling fan comes on. Test drive vehicle for approximately 10 minutes with engine speed at 1700-2500 RPM. If DTC P1491 resets, go to next step. If DTC P1491 does not reset, problem is intermittent. System is okay at this time. Check for poor connections or loose wires at EGR valve, harness connector located at right shock tower and PCM connectors.
  2. Turn ignition off. Disconnect EGR valve 6-pin connector. Start engine and allow to idle. Backprobing, measure voltage between EGR valve 6-pin connector terminals No. 4 (Pink wire) and No. 6 (Black wire). If battery voltage does not exist, go to next step. If battery voltage exists, substitute a known-good PCM and recheck. If DTCs do not reset, replace original PCM.
  3. Turn ignition off. Turn ignition on. Measure voltage between EGR valve 6-pin connector terminals No. 2 (Green/Black wire) and No. 3 (Yellow/Blue wire). If about 5 volts are present, go to next step. If about 5 volts are not present, measure voltage between 31-pin PCM connector terminals No. 18 (Green/Black wire) and No. 28 (Yellow/Blue wire). If about 5 volts are present, repair open circuit in wiring between EGR valve and PCM. If about 5 volts are not present, substitute a known-good PCM and recheck.
  4. Turn ignition off. Measure resistance between sensor side of EGR valve 6-pin connector terminals No. 1 (White/Black wire) and No. 2 (Green/Black wire). If continuity is not present, go to next step. If continuity is present, replace EGR valve.
  5. Measure resistance between EGR valve 6-pin connector terminals No. 1 (White/Black wire) and No. 3 (Yellow/Blue wire). If continuity is not present, go to next step. If continuity is present, replace EGR valve.
  6. Reconnect EGR valve connector. Turn ignition on. Measure voltage between 31-pin PCM connector terminals No. 6 (White/Black wire) and No. 18 (Green/Black wire). If about 12 volts are present, go to next step. If about 12 volts are not present, measure continuity between 31-pin PCM connector terminal No. 6 (White/Black wire) and ground. If continuity is present, repair short circuit in wiring between EGR valve and PCM. If continuity is not present, repair open circuit in wiring between EGR valve and PCM.
  7. Turn ignition off. Disconnect EGR valve 6-pin connector. Connect battery voltage to EGR 6-pin connector terminal No. 4 (Pink wire). Start and idle engine. Connect battery ground to EGR 6-pin connector 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.
  8. Turn ignition off. Disconnect 25-pin PCM connector. Measure continuity of Pink wire between PCM connector terminal No. 7 and EGR valve 6-pin connector terminal No. 4. If continuity is present, go to next step. If continuity is not present, repair open circuit in Pink wire between EGR valve and PCM.
  9. Measure continuity between 25-pin PCM connector terminal No. 7 (Pink wire) and ground. If continuity is not present, go to next step. If continuity is present, repair short circuit in Pink wire between PCM connector and EGR valve.
  10. Measure continuity between EGR valve 6-pin connector terminal No. 6 (Black wire) and ground. If continuity is present, replace PCM. If continuity is not present, repair open circuit in Black wire.
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