Firstly! This is not the ECU, I'm talking the CPU, which is by the pedals near the fuse box.

Mine and my replacement don't work. Or do they?

Since I bought my car, I have been fixing all types of issues here and there, and I can't pin this one down.

On a really hot day when the car has been basking in the sun, my CPU magically works. But even after a while it will crap out and all the features won't work. The lights on/keys in ignition beeper, horn and alternator failure feature (all the dummy lights come on) cease to function. I know that is controlled by the big circuit board in the CPU. I cleaned it with electrical contact cleaner, cleaned the contacts on the board and the harness. Still won't work. Sometimes I hear a faint beeping, or a clicking for the lights on/key in ignition warning. If I play with the wires on the harness the beeping might come on fully or disappear entirely. Other times I hear the relays for the horn clicking, but no horn will sound.

Like I mentioned it all works when it gets real hot out. I figure its because the contacts are expanding in places? I also tried 2 CPUs, they both behaved like this. Could it be my wiring? Should both CPUs be resoldered? I have the full FSM, but I am not good with electrical and have trouble even knowing what to look for as far as wiring diagrams and what not.

Please help!

 

Bad main board on the CPU. You can try re-soldering where the pins meet the circuit board, or just replace the main board (they are pretty cheap from Mazdatrix).

 

Does your website offer that service?