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DTC P1491: Insufficient EGR Valve Lift

  1. Perform PCM reset procedure. See PCM RESET PROCEDURE/CLEARING CODES  . 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. Keep engine speed at 1700-2500 RPM. If DTC P1491 resets, go to next step. If DTC 1491 does not reset, problem is intermittent, system is okay at this time. Check for poor connections or loose wires between EGR valve and PCM. Repair as necessary.
  2. Disconnect vacuum hose between EGR valve and EGR control solenoid valve from EGR valve. See the VACUUM DIAGRAMS article. Connect vacuum gauge to hose. Start engine and allow to idle. If vacuum exists, go to next step. If vacuum does not exist, go to step 5).
  3. Disconnect EGR control box connector (2-pin) located at right rear of engine compartment. Recheck for vacuum at disconnected EGR vacuum hose. If vacuum does not exist, go to next step. If vacuum exists, inspect hose routing of entire EGR system. See the VACUUM DIAGRAMS article. If all hoses are routed properly, replace EGR control solenoid valve.
  4. Turn ignition off. Disconnect PCM 26-pin connector. Check for continuity between ground and control box connector terminal No. 2 (Red wire). If continuity exists, repair short in Red wire between PCM 26-pin connector terminal No. 6 and EGR control solenoid valve. See the WIRING DIAGRAMS article. If continuity does not exist, substitute a known good PCM, then recheck. If symptom or indication goes away, replace original PCM.
  5. Connect vacuum pump to EGR valve. Start engine and allow to idle. Apply 8.0 in. Hg vacuum to EGR valve. If engine runs rough or stalls, and EGR valve holds vacuum, go to next step. If engine does not operate as specified, replace EGR valve.
  6. Turn ignition off. Disconnect control box connector (2-pin) located at right rear of engine compartment. Turn ignition on. Measure voltage between ground and control box connector terminal No. 1 (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 EGR control solenoid valve and 20-amp ECU fuse No. 4 (located in underdash fuse/relay box).
  7. Reconnect vacuum hose between EGR valve and EGR control solenoid valve to EGR control solenoid valve. See the VACUUM DIAGRAMS article. Connect vacuum gauge to hose. Start engine and allow to idle. Apply battery voltage to EGR control box terminal No. 1 (Black/Yellow wire). Observe vacuum gauge and apply battery ground to EGR control box terminal No. 2 (Red wire). If about 8 in. Hg of vacuum is present within one second, go to next step. If vacuum is not as specified within one second, go to step 9).
  8. Turn ignition off. Reconnect EGR control box connector. Reconnect vacuum hose between EGR valve and EGR control solenoid valve. See the VACUUM DIAGRAMS article. Start engine and allow to idle. Connect jumper wire between PCM 26-pin connector terminals No. 6 (Red wire) and No. 12 (Black wire). If engine stalls or runs rough, substitute a known good PCM, then recheck. If symptom or indication goes away, replace original PCM. If engine does not stall or run rough, repair open in Red wire between PCM and EGR control solenoid valve. See the WIRING DIAGRAMS article.
  9. Turn ignition off. Check EGR hoses for routing, restrictions, or leaks. See the VACUUM DIAGRAMS article. Repair or replace hoses as necessary. If hoses are okay, go to next step.
  10. Disconnect lower hose from EGR control solenoid valve and connect a vacuum gauge to hose. Start engine and allow to idle. If about 8.0 in. Hg of vacuum exists, replace EGR control solenoid valve. If about 8.0 in. Hg of vacuum does not exist, inspect vacuum hose between EGR vacuum control valve and intake manifold. See the VACUUM DIAGRAMS article. If hose is okay, replace EGR vacuum control valve.
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