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DTC P1509 (A/T & D16Y7): Idle Air Control (IAC) Valve

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  1. Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING DTCS in SELF-DIAGNOSTICS - INTRODUCTION article. Turn ignition on. If DTC P1509 is indicated, go to next step. If DTC P1509 is not indicated, problem is intermittent. System is okay at this time. Check for poor connections or loose wires at IAC valve and PCM connectors. See appropriate wiring diagram in WIRING DIAGRAMS article.
  2. Using backprobe set, measure voltage between ground and PCM 25-pin connector "B" terminal No. 10 (Black wire) and terminal No. 2 (Black wire), individually. See Figure. If one volt or less exists, go to next step. If more than one volt exists, check for open in wire(s) between PCM 25-pin harness connector "B" terminal(s) and ground connector, located at thermostat housing.
  3. Turn ignition off. Disconnect PCM 32-pin connector "A". Turn ignition on. Using backprobe set, measure voltage between ground and PCM 25-pin harness connector "B" terminal No. 15 (Orange wire) and terminal No. 6 (Black/Blue wire), individually. See Figure. If battery voltage exists, go to next step. If battery voltage does not exist, go to step  5.
  4. Turn ignition off. Disconnect IAC valve 3-pin connector. Measure resistance between IAC terminals No. 2 and No. 1, and terminals No. 2 and No. 3, individually. See Fig 1. If resistance is not 16-28 ohms, replace IAC valve. If resistance is 16-28 ohms, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
  5. Turn ignition off. Disconnect IAC valve 3-pin connector. Turn ignition on. Measure voltage between ground and IAC harness connector terminal No. 2 (Yellow/Black wire). See Fig 1. If battery voltage exists, go to next step. If battery voltage does not exist, check for open in Yellow/Black wire between IAC valve and PGM-FI main relay. See appropriate wiring diagram in WIRING DIAGRAMS article.
  6. Turn ignition off. Check for continuity in Orange wire between IAC valve harness connector terminal No. 1 and PCM 25-pin harness connector "B" terminal No. 15. Also check for continuity in Black/Blue wire between IAC valve harness connector terminal No. 3 and PCM 25-pin harness connector "B" terminal No. 6. See Figure and Fig 1 . See appropriate wiring diagram in WIRING DIAGRAMS article. If continuity exists, go to next step. If continuity does not exist, check for open in suspect wire between IAC valve connector and PCM 25-pin harness connector "B". See appropriate wiring diagram in WIRING DIAGRAMS article.
  7. Check for continuity between ground and PCM 25-pin harness connector "B" terminal No. 15 (Orange wire) and terminal No. 6 (Black/Blue wire), individually. See Figure. See appropriate wiring diagram in WIRING DIAGRAMS article. If continuity exists, check for short in suspect wire between IAC valve connector and PCM 25-pin harness connector "B". See appropriate wiring diagram in WIRING DIAGRAMS article. If continuity does not exist, go to next step.
  8. Measure resistance between IAC terminals No. 2 and No. 1, and terminals No. 2 and No. 3, individually. See Fig 1. If resistance is not 16-28 ohms, replace IAC valve. If resistance is 16-28 ohms, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
Fig 1: Identifying IAC Valve 3-Pin Connector Terminals
G96J09608Courtesy of AMERICAN HONDA MOTOR CO., INC.
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