Finding a strange fault

We always appreciate the feedback we receive from our customers. Thank you for taking the time from your day to review us! It makes it more worth while after finding a strange fault.

After a Mini was recovered to us with a seized alternator. This was a job to be carried out as soon as we could, as it was not booked in. The Battery was flat, we put the battery on charge for a few hours. We replaced the alternator and drive belt, then refitted the battery. Started the engine, now running fine with battery charging correctly.

However several systems were not working correctly afterwards such as dash lights, sounds and radio displaying disabled with no function. A full diagnostic test showed several control units on the K- Body Bus had no communication. A quick check of the main fuses for these systems showed all fuses are ok. We then called the customer explaining this issue. Fortunately they were honest stating this had been an intermittent fault in the past. With the fault now present, they were happy for us to investigate to locate & rectify the fault.

To start, we located the wiring diagram for the K- Body Bus with all control units listed on the bus. A quick test to see if one unit is bringing the system down is removing fuses/ power to each unit to see if the system returns on the diagnostics. Unfortunately this was unsuccessful with no change with fuses removed. The customer had mentioned the bc1/ general module control unit was suspected to be at fault in the past. With this in mind we headed to this first. Interchanged the unit with a used one we keep for testing. This made no change. With these easy tests made, we then needed to get deeper to check the K- Body bus.

After a mid update with the customer, they mentioned the fault had been intermittent and the vehicle had an aftermarket Bluetooth kit that had been removed. (Or so it should have been).
We checked the K- Body bus wire at the bc1 connector. It read 1.17 volts, which is very low as the bus should be battery voltage around 12 volts. Something was shorting to earth bringing down the voltage on the bus.

With the information from the customer, the next logical step was to check the radio where the Bluetooth kit ‘was’ fitted.
Moved radio out to find an additional wiring loom still present for the Bluetooth kit, but the unit had just been removed. We then disconnected the loom from the back of the radio wiring and BOOM, K-Body bus went back to 12 volts at the bc1 wire, as it should be. Removed the loom and refitted original wiring to radio. Refitted all parts correctly. Diagnostic check now shows communication to all units correctly with no faults. Dash lights, sounds and radio now working correctly. Fault rectified ?

We usually find with most electrical faults or battery drains, they are caused by aftermarket systems being fitted. With the help of the customer it allowed us to locate the fault faster!
It is always nice to be appreciated for our work! We’re here to help!

 

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