TECH TIP
BMW 745 Li Cranks, But Does Not Start – Brake Lights Stay On
Jun. 01 2021
Jun. 01 2021

Vehicle: 2003 BMW 745Li (E66), V8-4.4L (N62), Automatic Transmission/Transaxle

Mileage: 196,435

Problem: This vehicle arrived at the shop with a dead battery that had been drained while trying to start the engine.

Case Details: The technician installed and coded a new battery. Afterwards, the engine would crank over, but still not start. The technician retrieved the following diagnostic trouble codes (DTCs):

  • 285C (DME): Variable valve gear - CAN communication
  • 285D (DME): Variable valve gear - CAN communication, bank 2

He also noted that, with the new battery installed, the brake lights were on all the time. At this point, he called ALLDATA Tech-Assist.

The Tech-Assist consultant recommended using the scan tool to monitor the brake switch parameter identification data (PID) according to the Dynamic Stability Control (DSC) module. The tech found that DSC module would not communicate with the scan tool.

The shop had a known-good DSC module on the shelf. With the donor module plugged in, the brake lights remained off, and the car would crank and run, but the donor module could not be coded to the vehicle.

Confirmed Repair: The technician installed and coded a new DSC module and cleared all the DTCs. After that, the engine started and ran normally. No DTCs returned. Problem solved!

 

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