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DTC P1491: EGR System Malfunction: M/T

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  1. Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING DTCS in SELF-DIAGNOSTICS - 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. Drive 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 at EGR valve lift sensor and PCM connectors. See appropriate wiring diagram in WIRING DIAGRAMS article.
  2. Turn ignition off. Disconnect EGR valve lift sensor connector. Start engine and allow it to idle. Measure voltage between EGR valve lift sensor harness connector terminals No. 4 (Black wire) and No. 6 (Pink wire). See Fig 1. If battery voltage does not exist, go to next step. If battery voltage exists, substitute a known-good PCM and recheck. If symptom or problem goes away, replace original PCM.
  3. Turn ignition off. Turn ignition on. Measure voltage between EGR valve lift sensor harness connector terminals No. 2 (Green/Black wire) and No. 3 (Yellow/Blue wire). If 5 volts exists, go to next step. If 5 volts does not exist, replace EGR valve.
  4. Using backprobe set, measure voltage between ECM 16-pin connector "D" terminals No. 10 (Yellow/Blue wire) and No. 11 (Green/Black wire). If 5 volts does not exist, go to next step. If 5 volts exists, check for open in Green/Black wire between EGR valve lift sensor connector and ECM 16-pin connector "D".
  5. Turn ignition off. Measure resistance between EGR valve lift sensor terminals No. 1 and No. 2. See. Fig 1. If resistance is 100,000 ohms or higher, replace EGR valve. If resistance is not 100,000 or higher, go to next step.
  6. Measure resistance between EGR valve lift sensor terminals No. 1 and No. 3. See Fig 1. If resistance is 100,000 ohms or higher, go to next step. If resistance is not 100,000 or higher, replace EGR valve.
  7. Reconnect EGR valve lift sensor connector. Turn ignition on. Using backprobe set, measure voltage between PCM 16-pin connector "D" terminals No. 9 (White/Black wire) and No. 11 (Green/Black wire). If 1.2 volts exists, go to step  9. If 1.2 volts does not exist, go to next step.
  8. Using backprobe set, check for continuity between ground and PCM 16-pin connector "D" terminal No. 9 (White/Black wire). If continuity does not exist, check for open in White/Black wire between EGR valve and PCM 16-pin connector "D". If continuity exists, check for short in White/Black wire between EGR valve and PCM 16-pin connector "D".
  9. Turn ignition off. Disconnect EGR valve lift sensor connector. Using a fused jumper wire, connect battery voltage to EGR valve lift sensor terminal No. 6 (Pink wire). See Fig 1. Start engine and allow it to idle. Using a second fused jumper wire, ground EGR valve lift sensor terminal No. 4 (Black wire). If engine stalls or runs rough, go to next step. If engine does not stall or run rough, replace EGR valve.
  10. Turn ignition off and disconnect jumper wires from EGR valve lift sensor connector. Disconnect PCM 32-pin connector "A". Check for continuity in Pink wire between PCM 32-pin connector "A" harness connector terminal No. 7 and EGR valve lift sensor harness connector terminal No. 6. See Figure and Fig 1 . If continuity exists, go to next step. If continuity does not exist, check for open in Pink wire between PCM 32-pin connector "A" and EGR valve. See appropriate wiring diagram in WIRING DIAGRAMS article.
  11. Check for continuity between ground and PCM 32-pin connector "A" harness connector terminal No. 7 (Pink wire). If continuity does not exist, go to next step. If continuity exists, check for short in Pink wire between PCM 32-pin connector "A" and EGR valve. See appropriate wiring diagram in WIRING DIAGRAMS article.
  12. Check for continuity between ground and EGR valve lift sensor harness connector terminal No. 4 (Black wire). See Fig 1. If continuity does not exist, check for open in Black wire between EGR valve harness connector and ground connection located at thermostat housing. See appropriate wiring diagram in WIRING DIAGRAMS article. If continuity exists, substitute a known-good PCM and recheck. If symptom or problem goes away, replace original PCM.
Fig 1: Identifying EGR Valve Lift Sensor Connector Terminals (D16Y5 M/T)
G96H09607Courtesy of AMERICAN HONDA MOTOR CO., INC.
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