Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Buses And Control Units On The E90, E91, E92, E93
The most important buses on the E90 are: K-CAN, MOST, PT-CAN, F-CAN.
The new feature is that the footwell module (FRM) is connected to the PT-CAN. This is because:
- The adaptive headlights are integrated into the footwell module. The adaptive headlights need the high-speed PT-CAN.
- The longitudinal dynamics management sends the signal for the brake light on the PT-CAN.
Compared with the E87, some new control units are connected to the F-CAN, e.g. LDM and ACC (LDM: longitudinal dynamic management; ACC: active cruise control).
- > E90, E91, E92, E93: Buses and control units
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.