BMW Repair: DME and engine wiring harness, engine wiring harness, coolant level

Question
I have a 2002 BMW 540iT wagon. I had a 'low coolant level' issue a few times and took my car to a mechanic. He initially tried adding coolant, but the message came back, and I did not see any coolant leaking onto the floor under the car. He then diagnosed a faulty thermostat and coolant reservoir and replaced them. There were also other error codes as well that the computer was spewing out and the mechanic expected that all the errors would be fixed with these repairs.

The 'Service engine soon' light came on soon after. I took the car back to the mechanic and the only message he saw related to an air pump associated with the exhaust. He felt however, that the diagnosis was incorrect and wanted me to take the car to a dealer who would be able to get a more comprehensive fault-code listing from the computer. Before doing that, I took the car to an emission check place and they were not able to get readings from the computer.

When I took my car in to the dealership, they told me that the thermostat had leaked coolant that was wicked into the engine harness and had made it all the way to the DME (ECU). They could not get a reading from the computer either and claimed that the computer was actually shorted partially and had caused faulty error messages. They further state that the issue can only get worse and that I need to replace both the computer and the harness. They tell me that if I drive the car further, there is danger of me causing electrical damage.

Meanwhile the car continues to run great, and the 'Service engine soon' light is now gone after the dealer looked into the issue (dealer thinks this was caused by them just unplugging/plugging in harness). Even the emissions check place was able to hook up to my car computer and give me a clean chit.

The dealership wants $$$ for this job. Is there a way to reset the computer and recover.  Do I risk damage to the car by driving it around.  Does it make sense to get a used DME and harness if they really need replaced. Is there anyone other than the dealer who can do the job. I would think that the data from the old computer needs to be transferred over to the replacement ...

Thanks!

Answer
This is a common problem i see on all the V8 BMW's from about 1995-2002  The repair i do most common is replace the harness from the thermostat housing partway up to the DME. look at the wires and see how far up they are damaged. This is a very easy repair. ive only had to replace the harness and dme once and that was a severe case. It sounds like your damage was minimal. and no you cant install a used dme on that car, you need to find a good BMW independent shop that only works on BMW's to fix you're car, at our shop we have all the same dealer training and equipment, if you you would have come to our shop we would have replaced the thermostat and a short piece of harness along with a new connector for around $300.    hope this helps   Thanks Nathan