DTC P1491: EGR Valve Insufficient Lift 1. Reset the ECM/PCM. 2. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on. 3. Check for a Temporary DTC with the scan tool. 4. Test-drive the vehicle for approx. 10 minutes. Try to keep the engine speed in the 1,700-2,500 rpm range. Is Temporary DTC P1491 indicated? YES – Go to step 5. NO – 5. Turn the ignition switch OFF. 6. Disconnect the EGR valve 6P connector. 7. Start the engine and let it idle.
8. Measure voltage between EGR valve 6P connector terminals No. 4 and No. 6. Is there battery voltage? YES – Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original ECM/PCM. NO – Go to step 9. Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the EGR valve and the ECM/PCM. 9. Turn the ignition switch OFF. 10. Turn the ignition switch ON (II). 11. Measure voltage between EGR valve 6P connector terminals No. 2 and No. 3. Is there approx. 5 V?