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1994 Bonneville SE. Last week while driving at highway speed the engine died. Cranks but doesn't fire. Fuel pump runs and there's pressure at the schrader valve. Spark looks good at the coil packs. When I tried to scan for codes my reader just showed "error-check connection". This is a '94, so it's OBD 1.5. I've used this scanner on it successfully many times before and it works fine on another Bonneville, so I know it's not the scanner at fault. Another symptom is that when I turn the key to "run" both cooling fans run, which is not normal. Yesterday, while testing spark, fuel, etc, the battery was getting weak, so I took it out to charge overnight. When I put it back in the car, the engine started and ran normal for a few minutes. I put the scanner on it to check some values with key-on engine-off and after a few minutes it reverted to the former no-start state. At this point I can't think of any other possible cause for the "no start" than a failed ECM or bad connection/ground somewhere. I'm hoping someone here can advise me where and what to check next. Prior to this incident, the car has had the check-engine light on most of the time with two problems: cruise control only works intermittently, and the EGR valve malfunctions due to not getting the proper ground signal through the ECM. Any suggestions?

I think I would start with the ground busses near the bottom of the A pillars. Open and clean them up.

J Wikoff wrote:I think I would start with the ground busses near the bottom of the A pillars. Open and clean them up.

Thanks, I'll check those tomorrow.

Iirc, there are two + terminals on that battery setup - the eye goes to the maxifuse centre on firewall - make sure they have good connection.

Today I checked those ground busses and they both look clean and tight, wiggled the wires etc while cranking. No effect. Also, I cleaned and tightened the batt terminals as much as I can. No effect. Later, when I was hooking up a remote starter switch to test the injectors I noticed that the cooling fans didn't come on with the key on as they have been doing, and at that point I started the engine and it ran normally at idle for about 10 minutes, then died. Started right up again, ran about 5 minutes and died, started one more time then reverted to the no-start, no-scan, cooling fans running situation. While it was running I was able to scan it and there was stored trouble code: P0755-F31 Transmission Solenoid failure. This was surprising because I'd had the battery out overnight before and I thought that would erase all codes. Anyway, I hope it's not relevant. I've never had any trouble with the transmission on this car, unless that could have caused the original stall at highway speed. After that I tested the crank sensor with a voltmeter at the ICM wiring connector, it's apparently good. I swapped a known good ICM. No change. Then I began testing the injectors with a noid light and they apparently aren't getting the signal to fire. Does all this sound like anything other than a faulty ECM, or bad connection/ground?

I am vaguely remembering the fans running like that as a sign of something specific. It might be a bad pcm, I can't recall.

I've checked everything else I can think of, so I bought a used ECM on ebay and should get it in a couple days. I'll have my fingers crossed when I put it in because I don't know what else to do if that doesn't work. Thanks for the suggestions.

I put in the used ECM and that seems to have taken care of everything. It didn't look very promising. One of the connectors had part of the plastic broken off and several bent pins, but I straightened the pins enough to get the connector on. The transmission fault code must have been a glitch, it shifts fine and always has, and now the EGR valve and cruise control are working again too!