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DTC P1491: Insufficient EGR Valve Lift

  1. Connect and operate scan tester, following manufacturer's instructions. Clear codes. Operate engine at 3000 RPM until radiator fan come son. Drive vehicle, keeping engine speed at 1700-2500 RPM. Retrieve codes. If DTC P1491 appears, go to next step. If DTC 1459 does not appear, problem is intermittent. Inspect for poor connections or loose wires associated with EGR valve and PCM, then repair as necessary.
  2. Disconnect vacuum hose at EGR valve. Connect vacuum gauge to hose. Start and idle engine. If vacuum exists, go to next step. If vacuum does not exist, go to step 5).
  3. Unplug control box connector. Recheck for vacuum at disconnected vacuum hose. If vacuum does not exist, go to next step. If vacuum exists, inspect hose routing of entire EGR system. If all hoses are routed properly, replace EGR control solenoid valve.
    NOTE: When substituting a known-good PCM, immobilizer code must be rewritten using Honda PGM tester, or engine will not start.
  4. Turn ignition off. Unplug 26-pin connector from PCM. Test for continuity between ground and Red wire at control box harness connector. If continuity does not exist, temporarily substitute known good PCM, then retest system. If continuity exists, repair shorted Red wire between PCM terminal No. A6 and EGR control solenoid valve.
  5. Connect a vacuum pump to EGR valve. With engine idling, apply 7.8-8.0 in. Hg vacuum to EGR valve. If engine starts to run roughly or stall, and EGR valve holds vacuum, go to next step. If engine does not start to run roughly or stall, or EGR valve does not hold vacuum, replace EGR valve.
  6. Turn ignition off. Unplug control box connector. Turn ignition on. Measure voltage at Black/Yellow wire at control box harness connector. If battery voltage exists, go to next step. If battery voltage does not exist, repair open Black/Yellow wire between EGR control solenoid valve and fuse panel.
  7. With vacuum gauge connected to hose as in step 2), start and idle engine. Apply battery voltage to control box terminal No. 1 (Black/Yellow wire on mating harness connector). While observing vacuum gauge, apply ground to control box terminal No. 2 (Red wire on mating harness connector). If gauge indicates approximately 7.8-8.0 in. Hg within one second, go to next step. If gauge does not indicate approximately 7.8-8.0 in. Hg within one second, go to step 9).
    NOTE: When substituting a known-good PCM, immobilizer code must be rewritten using Honda PGM tester, or engine will not start.
  8. Turn ignition off. Reconnect wiring to control box. Restore vacuum hose connection to EGR valve. Start and idle engine. Connect jumper wire between terminals No. 6 (Red wire) and No. 12 (Black wire) at PCM harness connector "A". If engine stalls or runs roughly, temporarily substitute known good PCM, then retest system. If engine does not stall or run roughly, repair open Red wire between PCM and EGR control solenoid valve.
  9. Turn ignition off. Inspect EGR hoses for routing, restrictions, or leaks. If hoses are okay, go to next step. Repair or replace hoses as necessary.
  10. Disconnect lower hose from EGR control solenoid valve. Connect vacuum gauge to hose. Start and idle engine, If approximately 7.8-8.0 in. Hg vacuum exists, replace EGR control solenoid valve. If approximately 7.8-8.0 in. Hg vacuum does not exist, inspect vacuum hose between EGR vacuum control valve and intake manifold. If hose is okay, replace EGR vacuum control valve.
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