Questions and Answers
Honda Accord DTC P1491
Q. 1998 Honda Accord LX automatic transmission with 2.3 litre VTEC 189,000 miles code P1491 - EGR Valve Lift Insufficient Detected. I just made repairs to an exhaust leak that had previously caused a code P0420. The exhaust leak took a considerable effort to find because it was so small and was hidden by the heat shield.
Apparently one of the exhaust manifold studs broke during assembly at the factory (I bought the car new.) causing a very small leak. After replacing the broken stud and the exhaust manifold gasket the code P0420 was corrected.
The next day code P1491 showed up for an EGR valve problem. I am guessing that this is a coincidence because I never touched anything near the EGR valve.
I changed the spark plugs, air filter, oil, and oil filter a week before the exhaust manifold gasket was changed. Even though I check the oil regularly this car does not require additional oil to be added between changes so it is not an oil burner.
The engine runs fine and idles smoothly both hot and cold except for a very brief period of rough idle that lasts about 10 or 15 seconds just as the engine reaches a normal operating temperature, then it smooths out again.
I have not noticed any change in acceleration or gas mileage. I drive a lot on the highway and make a 166 mile round trip 5 days a week in this car. Except for the check engine light and code P1491 everything seems okay, but I need to be able to pass a Texas emissions OBD-II test soon. Any codes will result in automatic failure regardless of tailpipe emmisions.
Here is my question. How do I know that it is the EGR valve that needs to be replaced and not some other part could affect how the EGR functions? Are there tests that I could perform with basic equipment to confirm that the EGR valve is the culprit or to rule out other problems?
I would prefer to diagnose the problem correctly rather than change a whole bunch of good parts that don't need to be changed.
A. DTC P1491 - "EGR Valve Lift Insufficient Detected" is most often caused by a broken vacuum line going to the EGR valve. So I would check all the vaccum lines to be sure they are tight and not broken. Funny thing about vacuum lines, they never break out in the open, always behind or under something. Best way to check them is to remove them one at a time so you don't get mixed up and check them over carefully.
If the vacuum lines are good, you will need to check the electronics that operate the EGR system. It is an involved procedure, much too long to include here. Go to the library, in the Reference section, and get the Motors Import Service manual. That has the complete, step by step, procedure for checking the system. Or you can get a DIY subscription to Alldata which also has the complete, step by step, procedure.