Cavalier AF ECU failure

[siai47]

I started to notice long crank times in one of my Cavaliers a couple of weeks ago. They would sometimes exceed the eight second switchover to gasoline that is built into the computer. Finally, the car would not start at all--you could crank it until the battery went dead and it would never switch to gasoline. Removing the CNG fuse allowed normal operation on gasoline. Re-install the fuse and the car would instantly quit. There was no MIL (check engine light) and no DTC's. Checking with a scan tool showed no engine rpm readout from the AF ECU and a normal readout from the gasoline ECU. Both ECU's are feed from ignition module--wiring OK and signal at the AF ECU. Replaced the AF ECU with a known good one and the Cavalier is all happy again.

So what happened? The car was from a northeastern state and there was a fair amount of corrosion on the ECU. Taking the thing apart was difficult as the stainless screws were corroded into the aluminum housing. Finally got it apart and to my suprise, the entire inside of the housing was full of corrosion . The housing is sealed by an "O" ring. However, the road salt and water had wicked in between the cover and the body of the housing until it reached the "O" ring and from there continued past the "O" ring and into the interior of the housing. Parts of the aluminum housing and broken off around the edge and fallen into the bottom near the connectors. I believe that these pieces might have shorted out something on the board.

So, if you have one of these cars, it might be wise to prevent the problem I had. It is easy to get the ECU out of the car. Remove the drivers side headlamp and then one screw gets the ECU out. It is almost impossible to get the housing apart so the next best thing would be to clean up the area between the housing body and the cover with a wire brush. Then put a coating of silicone in the seam followed by a coating of paint on the ECU. Re-install the ECU making sure the seals on the connectors are in good shape. The replacement ECU's aren't cheap !

[siai47]

Re: Cavalier AF ECU failure

Update on my ECU failure. I bought a ECU off E-bay for a 2001 Cavalier. Installed it in my 2000---fired up fine and solved the problem. The donor Cavalier was from California and showed 213 K miles at the time of it's demise. Just for something to do today, I decided to remove the replacement ECU and check it for internal corrosion. As it was from an area that was fairly dry, I didn't expect corrosion problems with this ECU. I was able to remove the 10 buttonhead screws (metric) holding the housing together. To my surprise, this ECU also was starting to suffer from the same problems as my original ECU. Corrosion had reached the "O" ring seal and got past it in the lower right corner of the housing by the white connector. This is the same area that was completely dissolved in my original ECU. I removed the circuit board, cleaned the housing mating surfaces with drum sander, cleaned out the "O" ring groove, re-installed the board and applied silicone lube to the "O" ring. Most important, I put a small bead of Yamabond #4 sealer (available from Yamaha motorcycle/watercraft dealers) between the mating halves of the housing before putting it back together. This will prevent water from wicking between the housing halves and attacking the "O" ring groove with corrosion which allowed moisture into the housing. When I finished, I gave the ECU a coating of paint. Before I put the ECU back in the car, I noticed the PC board out of the original ECU was sitting on the bench. I had washed it in a bucket of soapy water a couple of days before and brushed all the aluminum oxide pieces off it it. I blew the board off with high pressure air, making sure there was nothing caught under the area where the connectors met the board. The board had a conformal coating on it so washing it shouldn't have killed it, but I wasn't going to use it again anyway. So, to make a short story long, the board was there, so was the car--so I plugged the board into the connectors, put the CNG fuse in and hit the starter. To my amazement, the car started right up on CNG . The housing was in bad shape, so I sandblasted it down to bare aluminum, painted the entire housing with zinc chromate primer, Did the Yamabond thing, put it all back together in the car and am driving it now .

The whole point of this narration is that there is a problem with the AF ECU housings that if left untreated, over time, will bring misfortune to all of us who own these cars. If the corrosion problem was only on cars from areas that use road salt to destroy our cars every winter, I wouldn't be concerned for everyone. However, taking apart the ECU from the California car with no visible outside corrosion and finding the same type of corrosion inside that was in my car from the Northeast set off alarm bells. You need to be proactive about this because things are not going to get better inside the ECU. If you don't feel comfortable getting inside the ECU, at a minimum you should consider cleaning the edges of the housing halves with a wire brush and putting a coating of silicone sealer in the gap. Just a word to the wise!

[jgwmkw]

Re: Cavalier AF ECU failure

Had the same problem with my cavalier. I believe the source of the corrosion is from being under the battery. Mine had a fairly old battery and had leaked some acid. Did you notice anything similiar?

[siai47]

Re: Cavalier AF ECU failure

Nothing from the battery in my Cavalier. It was due to the location right below the headlight and behind openings in the bumper. All the crud from the road ends up here. In addition, the design of the housing and the way it is sealed from the factory makes failure a long term sure bet .