Engine Controls - System & Component Testing: Diagnosis Honda Civic VI

Intake Air By-Pass (IAB) Control System Testing (Prelude)

1. Start engine and allow to idle. Disconnect No. 13 vacuum hose from IAB control diaphragm. See «VACUUM DIAGRAMS»(ref-16356) 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. See «VACUUM DIAGRAMS»(ref-16356) article. Check for vacuum at IAB vacuum tank. 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. Turn ignition switch off. Disconnect IAB control solenoid valve 2-pin connector. Measure voltage between IAB control solenoid valve harness connector terminals No. 1 (Black/Yellow) and No.2 (Red/Blue). 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 under-dash 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 scheme 1 If IAB control solenoid valve does not click when jumper wire is connected, repair open in wire between IAB control solenoid valve and PCM (A26). 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»(ref-16356) article. If vacuum does not exist, IAB control system 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 32-pin connector "A". see scheme 1 Check for continuity between ground and IAB control solenoid valve 2-pin connector terminal No. 2 (Red/Blue). If continuity exists, repair short in 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.

Intake Air By-Pass (IAB) Control Valve Inspection

Check valve shaft for binding and sticking, and ensure movement is smooth. Turn engine off. Ensure tab on IAB control valve contacts stop. (Scheme 38) Start engine and allow to idle. Ensure tab of IAB control valve contacts full-close screw. If any fault is found, clean linkage and shafts using carburetor cleaner. If problem still exists after cleaning, disassemble intake manifold and inspect IAB valve assembly.

Scheme 38

Float Test

Ensure fuel tank is less than half full. Remove fuel fill cap to relieve pressure, then reinstall cap. Remove left rear inner fender. Disconnect the On-Board Refueling Vapor Recovery (ORVR) vapor recirculation hose and connect a vacuum pump to the vapor recirculation hose. Plug vapor recirculation line. see scheme 10 Apply vacuum to the ORVR vapor recirculation hose. If vacuum holds, replace the ORVR vent shut valve. If vacuum does not hold, float is okay.

Valve Test

1. Ensure fuel tank is less than half full. Remove fuel fill cap to relieve pressure. Remove left rear inner fender. Disconnect the ORVR signal hose. Disconnect and plug vacuum hoses (A & C) from the EVAP control canister. Connect a vacuum pump to hose "D". see scheme 10 Pump vacuum pump 80 times. If vacuum does not hold, go to step 2).
2. If vacuum holds, connect a second vacuum pump to the ORVR signal hose (E). see scheme 10 Pump vacuum pump 1 time only. If vacuum is released on first vacuum pump, ORVR is okay. If vacuum is not released, replace the ORVR vent shut valve and retest.

See also:
• ON-VEHICLE ADJUSTMENTS