BMW 428i 4 Series (F32) Used Modules and a No Start

I was asked to code some used modules to a BMW 2015 428i that had been vandalised. The seats, instrument cluster, steering wheel, and turn signal and wiper switch cluster had been damaged and were replaced by ones removed from a parts car.

The car had a very large number of codes mostly from the replaced parts: the airbag light was lit along with the check engine light, the wipers ran constantly, and the turn signals did not work.

The code for the check engine light was caused by the leak detection pump not getting power. After examining the rear fuse box, I saw signs of water damage and when I removed the fuse box, the corroded leak detection pump wire broke off. The client said that he would replace the fuse box with the one from the parts car.

I advised that not all the parts were compatible do to the parts car being a different spec, and suggested that the damaged front of the old instrument cluster be removed and replaced with the one from the new one. And the old seat module put back, along with the original steering wheel and turn signal and wiper switch cluster. I also noticed that the driver's side seat belt tensioner had deployed when the parts car crashed, contributing to the airbag light when it had been installed in the client's car. After the parts were exchanged, many of the codes went away, and after the leak detection power wire was fixed, that code went away.

However, the car would crank and not start. I was quite sure that the fuel pump or the power to it, was at fault, I checked the voltage at the fuse, and it measured zero. The fuel pump fuse is powered by a relay in the rear fuse box that is switched by the front electronics module, this relay was open. I checked the relay coil voltage at the FEM and it was present, but it was not there at the rear fuse box, the wire from the FEM to the rear fuse box tested fine. After being confused for a little while, I then looked at the old fuse box to try and find the ground for the relays. I realized that the connector with the ground was not connected to the correct receptacle, so the relays would not close. After moving the connector, the car started. I realised that the connectors must have been swapped when the fuse box was changed.

This resolved the issues. All the warning lights went out, and the car worked perfectly.