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Home >> Honda >> 1997 >> Prelude Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Air Induction Systems >> Air Intake System >> Intake Air By-Pass (IAB) Control System Inspection
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Intake Air By-Pass (IAB) Control System Inspection

  1. IAB control solenoid valve is located at lower rear of engine. IAB control solenoid valve is off when engine speed is more than 4900 RPM. 2 Start engine and allow to idle. Disconnect No. 13 vacuum hose from IAB control diaphragm. No. 13 vacuum hose is located between IAB control solenoid valve and IAB control diaphragm. See VACUUM DIAGRAMS article. Check for vacuum at hose. If vacuum does not exist, go to next step. If vacuum exists, go to step 7).
  2. Disconnect No. 12 vacuum hose from IAB vacuum tank. Check for vacuum at IAB vacuum tank. See VACUUM DIAGRAMS article. If vacuum exists, go to next step. If vacuum does not exist, repair blockage or vacuum leak between IAB vacuum tank and intake manifold.
  3. Disconnect IAB control solenoid valve 2-pin connector. Measure voltage between IAB control solenoid valve harness connector terminals. If battery voltage is not present, go to next step. If battery voltage is present, replace IAB control solenoid valve.
  4. Measure voltage between ground and IAB control solenoid valve harness connector Black/Yellow wire. If battery voltage is present, go to next step. If battery voltage is not present, repair open in Black/Yellow wire between IAB control solenoid valve connector and fuse No. 14 (ECU CRUISE CONTROL) located in underdash fuse/relay box. See WIRING DIAGRAMS article.
  5. Turn ignition off. Reconnect IAB control solenoid valve 2-pin connector. Turn ignition on. Connect a fused jumper wire between PCM 32-pin connector "A" terminal A9 (Brown/Black wire) and terminal A26 (Red/Blue wire). See Figure. If IAB control solenoid valve does not click when jumper wire is connected, repair open in wire between IAB control solenoid valve and PCM. See WIRING DIAGRAMS article. If IAB control solenoid valve clicks when jumper wire is connected, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
  6. Increase engine speed to more than 5000 RPM. Check for vacuum at hose No. 13. See VACUUM DIAGRAMS article. If vacuum does not exist, solenoid is okay. If vacuum exists, disconnect IAB control solenoid valve 2-pin connector. Check for vacuum again. If vacuum does not exist, go to next step. If vacuum exists, replace IAB control solenoid valve.
  7. Turn ignition off. Disconnect PCM connector "A" (32-pin). See Figure. Check for continuity between ground and IAB control solenoid valve 2-pin connector Red/Blue wire terminal. If continuity exists, repair short in Pink/Blue or Red/Blue wire between PCM and IAB control solenoid valve 2-pin connector. See WIRING DIAGRAMS article. If continuity does not exist, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
    CAUTION: DO NOT  adjust IAB control valve full-close screw. It is factory preset.
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