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DTC P1491 - EGR SYSTEM MALFUNCTION Honda Prelude V

Testing & Diagnostics ~589 words
  1. Perform PCM reset procedure. See «TESTS W/CODES - INTRODUCTION»(ref-16345) 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. Test 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 between EGR valve connector and PCM. See «WIRING DIAGRAMS»(ref-16355) article.
  2. Disconnect No. 16 vacuum hose from EGR valve. See «VACUUM DIAGRAMS»(ref-16356) article. Connect vacuum pump/gauge to No. 16 vacuum hose. Start engine and allow it to idle. If vacuum does not exist, go to step 4). If vacuum exists, disconnect EGR solenoid valve 2-pin connector. Recheck for vacuum at No. 16 vacuum hose. If vacuum does not exist, go to next step. If vacuum exists, check EGR system vacuum hose routing. See «VACUUM DIAGRAMS»(ref-16356) article. If vacuum hose routing is okay, replace EGR control solenoid valve.
  3. Turn ignition off. Disconnect PCM 32-pin connector "A". Check for continuity between ground and EGR control solenoid valve 2-pin connector terminal No. 1 (Orange wire). If continuity exists, repair short in Orange wire between EGR control solenoid valve and PCM 32-pin connector "A" terminal A7. See «WIRING DIAGRAMS»(ref-16355) article. (Схема №1) If continuity does not exist, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.
  4. Connect vacuum pump/gauge to EGR valve. Start engine and allow it to idle. Apply 8.0 in. Hg vacuum to EGR valve. If engine stalls or runs rough, and EGR valve holds vacuum, go to next step. If engine does not stall or run rough, or EGR valve does not hold vacuum, replace EGR valve.
  5. Turn ignition off. Disconnect EGR control solenoid valve 2-pin connector. Turn ignition on. Measure voltage between ground and EGR control solenoid valve 2-pin harness connector terminal No. 2 (Black/Yellow wire). If battery voltage exists, go to next step. If battery voltage does not exist, repair open in Black/Yellow wire between EGR control solenoid and No. 14 ECU/EAT ECU (15-amp) fuse located in underdash fuse/relay box. See «WIRING DIAGRAMS»(ref-16355) article.
  6. Reconnect vacuum pump/gauge to No. 16 EGR valve vacuum hose. See «VACUUM DIAGRAMS»(ref-16356) article. Start engine and allow it to idle. Using a fused jumper wire, connect battery voltage to EGR control solenoid valve 2-pin connector terminal No. 1 (Black/Yellow wire). While observing vacuum gauge, connect battery ground to EGR control solenoid valve 2-pin connector terminal No. 2 (Red wire). If there is not about 8 in. Hg vacuum within one second, go to next step. If there is about 8 in. Hg vacuum within one second, go to step 8).
  7. Turn ignition off. Inspect vacuum hoses No. 16 and 24 for proper routing, leaks or restrictions. See «VACUUM DIAGRAMS»(ref-16356) article. Repair hoses as necessary. If hoses are okay, replace EGR control solenoid valve.
  8. Turn ignition off. Reconnect EGR control solenoid valve 2-pin connector and No. 16 vacuum hose to EGR valve. Start engine and allow it to idle. Using a fused jumper wire, connect PCM 32-pin connector "A" terminal A7 (Orange wire) and terminal A10 (Black wire). If engine does not run rough or stall, repair open in Orange wire between PCM connector terminal A7 and EGR control solenoid valve. If engine runs rough or stalls, substitute a known-good PCM and recheck. If symptom or indication goes away, replace original PCM.

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