EGR System Malfunction
DTC P1491: Malfunction in EGR SystemSpecial Tools Required
Vacuum Pump/Gauge, 0 - 30 in.Hg A973X-041-XXXXX
1. Do the ECM/PCM Reset Procedure.
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 the Temporary DTC with the scan tool.
4. Drive the vehicle on the load 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-Intermittent failure, system is OK at this time.
Check for poor connections or loose wires at the EGR valve and the ECM/PCM.
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 the 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.
Diagnostic Strategies
NO-Go to step 9.
9. Turn the ignition switch OFF.
10. Turn the ignition switch ON (II).
11. Measure voltage between the EGR valve 6P connector terminals No.2 and No.3.
IS there approx. 5 V?
YES-Go to step 13.
NO-Go to step 12.
12. Measure voltage between the ECM/PCM connector terminals C18 and C28.
Is there approx. 5 V?
YES-Repair open in the wire between the EGR valve and the ECM/PCM (C18).
NO-Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original ECM/PCM.
Diagnostic Strategies
13. Turn the ignition switch OFF.
14. At the sensor side, measure resistance between the EGR valve 6P connector terminals No.1 and No.2.
Is there continuity or resistance of 100 kOhm or higher?
YES-Replace the EGR valve.
NO-Go to step 15.
15. Measure resistance between the EGR valve 6P connector terminals No.1 and No.3.
Is there 100 kOhm or higher?
YES-Replace the EGR valve.
NO-Go to step 16.
16. Reconnect the EGR valve connector.
17. Turn the ignition switch ON (II).
18. Measure voltage between the ECM/PCM connector terminals C6 and C18.
Is there approx. 1.2 V?
YES-Go to step 19.
NO-Repair short in the wire between the EGR valve and PCM (C8).
19. Check for continuity between ECM/PCM connector terminal C6 and the EGR valve 6P connector terminal No.1.
Is there continuity?
YES-Go to step 20.
NO-Repair open in the wire between the EGR valve and ECM/PCM (C6).
20. Turn the ignition switch OFF.
21. Disconnect the EGR valve 6p connector.
22. Connect the battery positive terminal to EGR valve 6P connector terminal No.4.
23. Start the engine and let it idle, then connect the battery negative terminal to the EGR valve 6P connector terminal No.6.
Does the engine stall or run rough?
YES-Go to step 24.
NO-Replace the EGR valve.
24. Turn the ignition switch OFF.
25. Disconnect the ECM/PCM connector B (25P).
26. Check for continuity between ECM/PCM connector terminal B7 and the EGR valve 6P connector terminal No.4.
Is there continuity?
YES-Go to step 27.
NO-Repair open in the wire between the EGR valve and the ECM/PCM (B7).
27. Check for continuity between ECM/PCM connector terminal B7 and body ground.
Is there continuity?
YES-Repair short in the wire between the EGR valve and the ECM/PCM (B7).
NO-Go to step 28.
28. Check for continuity between the EGR valve 6P connector terminal No.6 and body ground.
IS there continuity?
YES-Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original ECM/PCM.
Diagnostic Strategies
NO-Repair open in the wire between the EGR valve and G101.