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Steve, BMW Expert
Category: BMW
Satisfied Customers: 23695
Experience:  BMW Expert
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My '99 E39 has a problem, where the ASC, ABS and

Customer Question

Hi, my '99 E39 has a problem, where the ASC, ABS and transmission warning lights light up. When this happens, the car can't change gear, and the sppedometer does not Work. I have read out ther faults, and there are a heap of CAN faults in all ECUs. If I read out the faults while the fault is present, there is no contact with these ECUs
JA: How old is the transmission? Have you checked the brake switch?
Customer: This has no bearing on the CAN communication problem. When the fault is present, there is obviously no CAN communication
JA: What is the model of your '99 BMW?
Customer: 523i
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I am a Mercedes technician, so yes. I have already described what I have tried, I am thinking about putting a scope on the CAN lines to see what happens to the signal
Submitted: 10 months ago.
Category: BMW
Expert:  Steve replied 10 months ago.
Hello and welcome,
My name is ***** ***** it will be my pleasure to assist you today.
I will provide an honest answer. I trust this will be appreciated. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.
Thank you for your attention to the rating requirement.
The problem is almost certainly a failed abs module so I would replace it or send it out for repair
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.
Customer: replied 10 months ago.
Hi again,
It seems, while the fault is present, the whole CAN network is down, as there is no contact with any of these ECUs at the time. Do you think it is in the ABS ECU that CAN is being shorted? I have also heard it could be the alternator, producing uneven current?
Expert:  Steve replied 10 months ago.

It would most commonly be the ABS unit. The alternator could be tested when the issue is present to see if it is fluctuating, but I do not believe this is likely the cause. Please do not forget to CLICK ON a positive rating