Year/Model
1999 BMW 528I Wagon
Problem
Transmission Fault light
History
Customer arrived in shop originally with brake lights stuck on. Checked vehicle computer and found faulty switch. Replaced switch with no problems for one month. Customer comes back to shop with radio not functioning and transmission fault light on.
Diagnostic
Plugged in vehicle scanner and found code for brake light switch short. Checked wiring at switch with no issues. Found strange problem where brake lights would stay on and radio not functioning. Checked vehicle computer and found no communication with many vehicle system such as abs, srs, traction control, radio, wipers.
Common problems with BMW is to have a fault in the CAN Bus system. The CAN bus is a communication system within the vehicle that allows for data transfer between different components. It is similar to a highway. If there is a traffic jam or component that is shorting and constantly transmitting data, no other system will be allowed to communicate with each other.
The way to figure out which one is jamming the system is to find the hub and disconnect one at a time. Once disconnected you need to restart the car and see if its functioning again. The hub for the CAN Bus is usually behind the glove box. The wires are connected to a piece of metal that has multiple tabs on them. The wire is solid white with red stripes and yellow dots.
We disconnected each lead and tested the system with no change. Usually we find one that is the problem and easily fixed. Since so many systems are not connected we had to move on. We them proceeded to test the power going to the modules. We found intermittent power at each. Tracing further back to the ignition system we found that jiggling the wiring at the ignition switch would cause the systems to come back online. We found the electrical part of the ignition to be the problem. Our part number was 61 32 6 901 961. Sorry that i do not have a picture attached.
Repair
Removed and replaced ignition switch electrical assembly. Tested vehicle, ok at this time.
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