So I replaced the blown OBC fuse in the fuse box, and replaced the capacitor in the correct polarity, and tada, the matrix board worked great, the AC controls were restored to normal (i.e. not flashing), and the car still ran fine.

I drove the car for several trips over the next 36 hours with no further problems. When trying to start the car in the cold morning, the car wouldn't start - as if the timing was terribly screwed up. I towed the car to a non-dealer shop, who replaced the coil packs... still no start. (They also found the check engine light had been removed.)

The questions I have:

1. If the motherboard fiasco smoked the ECU/DME, why did the car run for several trips, or is this just a coincidence?

2. If the ECU is replaced, could an otherwise symptom-free problem with the motherboard redamage the new ECU? Does this motherboard provide any signals to the ECU other than thru the previously missing CHECK ENGINE light? Or is this just a coincidence since 4 of the 6 secondary coils were bad? (The shop told me a fried ECU is often a result of these "bad coils".)

3. If I can find a replacement ECU with the same serial number from another similar 525i, does it have to be "recoded" by the dealer for my specific car?

ANY light that can be shed on this sad story would be greatly appreciated. Further info:

this is an M50 engine with ~ 160,000 K.

Thanks,

Wallace Martin
sallgdon64@hotmail.com