DTC Troubleshooting: P1491 (12-3)

DTC P1491 (12-3):  EGR Valve Insufficient Lift

1.Reset the ECM/PCM.

2.Start the engine. Hold the engine at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on.

3.Drive the vehicle under load for about 10 minutes. Try to keep the engine speed in the 1,700-2,500 rpm (min-1) range.

4.Check the Temporary DTC with the HDS or the scan tool.

Is Temporary DTC P1491 indicated?


YES - Go to 5.


NO - Intermittent failure, system is OK at this time. Check for poor connections or loose terminals at the EGR valve and at the ECM/PCM.n


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 - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original  ECM/ PCM.n


NO - Go to 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 about 5 V?


YES - Go to 13.


NO - Go to 12.


12.Measure voltage between ECM/PCM connector terminals A10 and A20.

 

Is there about 5 V?


YES - Repair open in the wire between the EGR valve and the ECM/PCM (A10, A20).n


NO - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original  ECM/ PCM.n

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 kW or higher?


YES - Replace the EGR valve.n


NO - Go to 15.


15.Measure resistance between the EGR valve 6P connector terminals No. 1 and No. 3.

 

Is there 100 kW or higher?


YES - Replace the EGR valve.n


NO - Go to 16.


16.Reconnect the EGR valve connector.

17.Turn the ignition switch ON (II).

18.Measure voltage between ECM/PCM connector terminals A10 and A13.

 

Is there about 1.2 V?


YES - Go to 22.


NO - Go to 19.


19.Turn the ignition switch OFF.

20.Disconnect ECM/PCM connector A (31P).

21.Check for continuity between ECM/PCM connector terminal A13 and body ground.

 

Is there continuity?


YES - Repair short in the wire between the EGR valve and the ECM/PCM (A13).n


NO - Repair open in the wire between the EGR valve and the ECM/PCM (A13).n

22.Turn the ignition switch OFF.

23.Disconnect the EGR valve 6P connector.

24.Connect the battery positive terminal to the EGR valve 6P connector terminal No. 4.

 

25.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 26.


NO - Replace the EGR valve.n


26.Turn the ignition switch OFF.

27.Disconnect ECM/PCM connector B (24P).

28.Check for continuity between ECM/PCM connector terminal B14 and body ground.

 

Is there continuity?


YES - Repair short in the wire between the EGR valve and the ECM/PCM (B14).n


NO - Go to 29.

29.Connect the EGR valve 6P connector terminal No. 4 and body ground with a jumper wire.

 

30.Check for continulty between ECM/PCM connector terminal B14 and the body ground.

 

Is there continuity?


YES - Go to 31.


NO - Repair open in the wire between the EGR valve and the ECM/PCM (B14).n

31.Disconnect the jumper wire from the EGR valve 6P connector.

32.Connect the EGR valve 6P connector terminal No. 6 to body ground with a jumper wire.

 

Is there continuity?


YES - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original  ECM/ PCM.n


NO - Repair open in the wire between the EGR valve and G101.n