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Q: BMW E39 has no response

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I have a problem. BMW E39 has no response. I've tried to scan it with my diagnostic tool. I can't scan it at all. The box is in safe mode. I expect the ECU is bad but I'd like to know your opinion.

A: Yes, it probably is the main computer. It’s...

Yes, it probably is the main computer. It’s a really common problem. If you can’t get any response from the scan tool, there are really only three things that can go wrong: the main computer could be bad, the wiring between the main computer and the sensor in your data port could be shorted out, or you’ve got a bad sensor that shorted the whole thing out.

Rather than start with buying a brand new computer, my advice is to go through each of the sensors in the car with the key turned on, and unplug them one at the time. When you unplug one of them and suddenly the scanner can diagnose and start getting data from the computer, this will mean that a sensor is bad. In this case you’ll need to replace that sensor first. This is how I test them so you will want to try it out and fix that first, rather than buying an expensive new compressor or a new ECU on a guess.

You don’t want to guess with something that expensive. I’d recommend having a certified technician diagnose why you’re car is not responding and make any necessary repairs.

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