My SES light used to be intermittent but recently has been coming on almost 100% of highway dtiving. The only code present in the PCM was 13. I changed the O2 with a Delco unit and took it for a quick 3 mile drive. No light. I decided to try the highway and sure enough just as I entered, the light came on.

Reading the manual I find the instructions to connect to a tester which I do not have so I'm looking for some other ideas. I see the O2 ground is suppose to ground at the "trans stud". I'm a little lost on that location.

I thought that the O2 was grounded through the exhaust pipe itself?

The diagram shows PCM pin BD3 goes to the purple wire of the O2 and pin BD2 is the ground for the O2. It is basically a ground reference right at the PCM not at the sensor.

Make check your PCM'* ground?

I did some more testing today. Continuity and resistance tests. I could find no abnormal results. I also used a Dremel and wire brush attachment to clean all the ground terminals, mounts, star washers and nuts for the 4 grounds under the hood and the one in the right kick panel. Although this helped lower the resistance to the ground terminals to the PCM, it did not solve the SES light problem.

This points to the PCM as the culprit. I noticed a refurb sticker on the case so that is probably the last nail in the coffin for that damn thing. Any other suggestions before I look for a new PCM?

The problem has been resolved. A PCM swap did the trick.

I did learn something today too. The guy at the junkyard gave me a list of compatible vehicles that are supposed to have the same PCM. I questioned the list when I saw the Lesabre and Trans Sport on there too. He said that it didn't make a difference whether it was an L67 or L27. I really thought this was a crock of dung but went ahead and grabbed one from a 93 Olds LSS with a VIN code of "L".

I came home and realized that the PCM I already had from the parts car has the same service code as the one from the LSS. I figured I'd give it a shot and what do you know, it works fine. All I had to do was change the chip.

Glad you got it fixed. That could be a pesky one to solve. PCM'* are widely universal in a block of years (or PCM types) across vehicles. The Eprom is the specific thing from model to model.

How much was the new PCM?

Only $20. The place in Worcester is Linder'* and directly across the street is Sams U Pull or something like that. I believe they are under the same ownership. The newer parts are removed and inventoried at Linder'* and the remains and older models are picked apart across the street. It would have been $60 had I not wanted to pull it myself.

Yea Don, those PCMs are tricky. He gathered that information from his computer and said that it was very reliable. I'd love to get my hands on THAT software. Know anyone that works/owns a boneyard?