Hi,
I recently just bought a 1995 oldsmobile 88 with the 3800 with only 29000 miles. I have this intermittent check engine light the comes on but will turn off when you restart the car or stay on for about three trips then shuts off. I scanned the computer with the actron cp9690 and the codes are P0401 and P1406. The egr was just replaced with a Gm one. What should I check next?
Work recently done
Lower intake gaskets
upper intake
coolant elbow
pcv valve
valve cover gaskets
thermostats and radiator hoses
Ac compressor replacement
EGR valve

Possible air flow restriction?: Was there carbon build ups along the bottom of the old EGR ?
I would want to remove the throttle body, use some carb cleaner & ensure nothing is plugged up.
Carbon can build up inside at (A) and run a thin coat hanger towards (B) EGR port

Soft Ride, I don't think that is a picture of a 3800 engine....

But you could be right about carbon buildup in the passageway........I've seen this mainly happen in 3.1/3.4'* not 3800'*, because the openings are much bigger.....

Since EGR was replaced, I would be checking the harness connectors to the EGR, and also the wires for breaks.....could also be a bad PCM.....

29,000 miles in 23 years tells me likely lots and lots and lots of short trips therefore likely lots of carbon build up from the injectors to the tailpipe.

I'd wonder what the oxygen sensors look like. Probably not related but might be good to check.

I checked the passage ways when i did the intake it was pretty clean not much carbon. I thought a bad pcm would cause the car to not start or idle?

I thought a bad pcm would cause the car to not start or idle?




You did not say this in original post....

The car drives just fine its just about the 3rd trip or so the check engine light comes on until i shut off the car. Then if i restart it the light is off until i make about 3 trips

Okay so what we have here is a low-mile L36 posting a P0401 and P1406 but otherwise running fine, correct?

Were these codes showing before or after all of the above repairs were done?

If the codes were showing before the repairs, were they cleared as part of the repairs?

Did you perform all of the repairs?

Have you tried clearing the codes to see if they repost?

I agree with Tech II: Check the wires and harness leading to the EGR. I suggest checking everything else around all of these repairs as well.

If you haven't already, take this poor car out on the freeway and drive to Sacramento and back to give it a chance to really warm up and clean itself out. I imagine a lifetime of short trips in the bay area in salt air haven't done sensors, connectors, and the catalytic converter any favors.

The codes were there before the repair and they were cleared when i disconnected the battery to do the repairs. All the repairs were done by me. I cleared the codes and they will come back in about 3 trips. Ever since Ive got the car all I have been doing is using it a freeway vehicle once or twice a week , it rarely sees any city driving. What is the best way to check the egr harness?

Good to hear it sees freeway miles. That rules some current contributing factors out.

Best way to check the harness is first look for big obvious damage, then grab a meter and set it to continuity and test from one end of each wire to the other with the ignition off.