I have a 1990 Oldsmobile Delta 88 With the 3800 LN3 motor. I can’t seem to figure out this quad driver module A fault. For the last 2 years my engine light has been turning on and then off over and over. Last night the engine light was turning on and off with the car in park and idiling in the driveway. The only code I have other than the regular code 12 is code 26. I swapped the computer with another one I had and that made no difference. I have the original GM service manual from 1990 with wiring diagrams. Recently my fuel Vapor Purge Solenoid has been clicking like crazy but that might be a separate issue as the engine light goes off while it lis clicking. The car runs perfect even when code 26 is thrown. The car has been my daily driver for the past 2 years now with almost no issues! Any help would be greatly appreciated.

Thank You,

Matt

My first guess would be the ECM, but hopefully you replaced it with one that didn't have a similar problem.....

Since you have a manual and wiring diagrams, you have to test it the old fashion way.......each circuit that the quad driver controls, you will have to insert an ampmeter, and monitor the circuit for 10 minutes to see if you have a spike or dramatic change in amperage.....

I like a good challenge! Ok, let’* say I find that one of the circuits controlled by Quad Driver Module A has a voltage spike, what would that indicate? What would the next step be?

Thanks for the Help!

Matt

Well, for example, suppose one of the circuits is some type of solenoid...and suddenly the solenoid shorts out.....current will increase and the quad driver will shut down....the fix is replace the solenoid...

Ok, I see! I know what I’ll be working on this weekend. I’ll keep you posted!

I'm a little late, but I should share that a replacement EGR Valve fixed this problem. Hopefully that information will help someone else out there.

Matt

It helps out a lot when people come back and post replies.

Yes, thanks for letting us know!

It started out as just code 26 and after a long time code 63 popped up as well. Code 63 indicates a problem in circuit number 697 which is the blue wire on the EGR valve. I traced that wire back to the computer which happens to be pin number BD2 on the ECM. The wire had good continuity and no shorts to ground that I could see so I replaced the EGR and the service engine soon light never came back on!

Good backstory. Sometimes a good diagnosis just involves waiting for it to get worse or for something else to happen to fill in the gaps.