Electrical mystery

I have a 1998 Subaru Forester, 140,000 k. It’s at a really good shop now because, now and then, it just turns off. When it does that, it puts out codes about things that are not wrong. The shop found several bad grounds and fixed them and it was fine for a while. But it did it again, and set the AT Oil Temp light flashing (there is not a problem with that part of the car). So now we are deciding to just replace the wiring circuit that connects the parts that are involved, which include most of the important parts of the car. The hope is that redoing every connection will get rid of the bad one. I have $$ in this now and no way to get them back if I try to sell it, even if I would do that with this problem. The replacement is a max of $400. The shop really knows Subarus, but I figured I would ask to see if anyone has an idea of how to track down the problem, or if there is another possible answer.

Bad ground connections are fairly common troubles with these cars. I wouldn’t replace the wiring unless you first verify the trouble is with it. You may end up still having the trouble after paying out the cash. Instead of replacing the wiring I suggest you have the shop clean every ground connection under the hood, particularly the grounds on the engine. Hopefully that will clear the trouble. The trouble may also be due to a faulty Main Relay so you should replace it also. It supplies power to the ECU and various critical engine components.

Thanks I am checking with my guys.

There’s not nearly enough info known to me about this problem so as to be able to even make a half-educated guess.

However, it seems to me that they could be over-analyzing this problem. Many times what appears to be a major electrical headache often has a very minor root cause and I’m in agreement with Cougar about not replacing the wiring.

Corroded ground connection, maybe even a corroded battery cable connection, or even a failing fusible link could cause this kind of problem. A fusible link can develop an erratic connection over time when age and heat starts to cause a problem when solder starts to melt inside of the link.
Many Asian cars use links like the one in the picture.

Sometimes this can be seen when the little plastic cover is popped off of the link and the internals examined very closely.
While I realize this has been little or no help at all, I do have a strong gut feeling that this problem is actually comparatively minor and is being overblown. That’s certainly easy to do with electrics on modern cars.