BMW X1, 2021
No crank after a body control unit swap: three faults stacked
An auction X1 with no power and no crank, after someone had already replaced the body control unit: wrong software in it, a missing transmission fuse, and no spark plugs.
What the customer reported
Bought at auction, and it had no power. Someone had come out and replaced the body control unit, but the car still did not crank at all.
What it actually was
Three things, stacked on top of each other.
The body control unit had the wrong software installed.
The main fuse for transmission power, 15 amps, in the glove box, was missing, so the transmission module had no power and no communication.
All four spark plugs were missing.
How it was found
I checked the software first and found the wrong software in the body control unit, so I programmed it. After that we had power and communication on almost all control units, except the transmission.
On this car the transmission module sits on top of the transmission itself. I checked its power, bus communication and ground: no power at all. In the glove box, the main fuse for transmission power was missing. With a 15 amp fuse in, the transmission got communication and the car cranked.
It cranked but did not start, and way too fast, like no compression. With the top cover off, all four spark plugs were missing. Plugs in, and it fired up.
