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DTC P1508: Idle Air Control (IAC) Valve

WARNING: This page is about a different car, the 2000 Honda Prelude. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING DTCS in SELF-DIAGNOSTICS - INTRODUCTION article. Start engine and warm to normal operating temperature. If DTC P1508 is indicated, go to next step. If DTC P1508 is not indicated, problem is intermittent. System is okay at this time. Check for poor connections or loose wires at IAC valve connector and PCM connector. Also check poor connections or loose wires at C283 connector, located at right shock tower. See appropriate wiring diagram in WIRING DIAGRAMS article.
  2. Turn ignition off. Disconnect IAC valve 2-pin connector. Turn ignition on. Measure voltage between ground and IAC valve harness connector terminal No. 2 (Yellow/Black wire). If battery voltage exists, go to next step. If battery voltage does not exist, repair open in Yellow/Black wire between IAC valve connector and PGM-FI main relay. PGM-FI main relay is Brown and is located under left side dash, left of steering column. See appropriate wiring diagram in WIRING DIAGRAMS article.
  3. Turn ignition off and reconnect IAC valve 2-pin connector. Disconnect PCM 32-pin connector "A". See Figure . Turn ignition on. Measure voltage between ground and PCM 32-pin harness connector "A" terminal No. 12 (Black/Blue wire). If battery voltage exists, go to next step. If battery voltage does not exist, repair open or short in Black/Blue wire between IAC valve connector and PCM 32-pin connector "A". See appropriate wiring diagram in WIRING DIAGRAMS article.
  4. Momentarily connect a fused jumper wire between PCM 32-pin connector terminals No. 10 (Black wire) and No. 12 (Black/Blue wire), several times. See Figure . If IAC valve does not click, replace IAC valve. If IAC valve clicks, substitute a known-good PCM and recheck. See SUBSTITUTING PCM under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - INTRODUCTION article. If symptom or indication goes away, replace original PCM.
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