Replacing a faulty Range Rover Sport BCM
One of the significant problems of modern cars is the amount of electronic control units which are depending on each other in one or multiple ways. Failiure of a single unit can ground the car reliably, where the dealer will ask you thousands of $ getting it fixed.
In this case we were facing a 2007 Range Rover Sport TDV8, where the electrical rear windows were inoperative. The customer already indentified the Body Control Module himself as the culprit and provided us with an “identical” spare unit, asking for making it work.
Little details – big problems
Beside the instrument cluster, the Body Control Module (or BCM) is the brain of the car. It controls very many assessories including the vehicle alarm and immobiliziation.
Each BCM comes pre-programmed from the factory, already containg a number of remote control keys, stored for operation.
In a case where both original keys get lost, the dealer can send you a replacement based on the data stored in your BCM and his database. Adding an other key from ebay or any other source with dealer tools is impossible.
So its logical, that this information inside the BCM can’t get changed easily. It needs to be present for the lifetime of the car. In other words: replacing a BCM is a tough job which requires tools and experiences far bejond the dealer level.
Challenge accepted…
For making the spare BCM work in the car, we first need to extract all neccessary information from the original BCM. For example the vehicle identification number (VIN) and the codes of the accepted remote keyfobs are stored deeply inside some tiny chips of the BCM. In case the VIN stored inside the BCM doesn’t match the VIN stored inside the instrument cluster, the car won’t run. Without the proper key codes from the original remotes, the engine won’t start up.
For getting this information, you need to directly contact the relevant IC and extract the data by low level debugging. This requires specialized tools and experience when soldering a number of cables to the delicate PCB.
Once the data is copied, the same is done with the spare unit and the data written into the IC memory. Now we have a BCM which will accept the remotes and offers the correct VIN.
Next step is to copy the original car configuration onto the spare BCM. When reading the content of the spare BCM memory it bcame obvious, that it came from a Discovery 3 and not from a Range Rover.
So we used some dealer tools for having the spare BCM flashed as if it simply would get a software update. Unfortunately the newer BCM now runing with the latest firmware, required a number of other modules to be updated as well, otherwise no proper co-operation was possible.
After updating the Engine Control Module, Instrument Cluster, Automatic Transmission Controller, Steering Column … the car finally started up properly and without any errors.
Job done!
