Power Window & Mirrors Inoperative | BMW E90


🚗 2011 BMW 328i (E90)

  • Front driver side power window doesn’t work
    • Passenger, and both rear windows could be operated from their own switches, but not from the driver’s switch.
  • Both power mirrors don’t work
  • Drivers power switch was totally inoperative.


🩺 Diagnosis

Footwell module (FRM) had 3 codes:

  • LIN Bus communication line with left mirror, disrupted
  • LIN Bus communication line with right mirror, disrupted
  • LIN Bus communication line with drivers power switch, disrupted


Driver’s power windows could be operated by the scanner. So, it rules out windows motor, footwell module, and power/ground/ to those components.

First, I tested for a good power and ground at the driver’s switch connector. All present.

Then I decided to check the LIN Bus

  • Lin bus is the network that the switch communicates through with other modules in the car. Without it working properly nothing on the driver’s master switch will work.
  • Testing revealed that LIN bus didn’t transmit any data to the footwell module when pressing any of the switch’s buttons. The line was at a constant ~7V. This is our clue.
  • Why there was no data transmission on the LIN Bus?

Here is a diagram for Power Windows, and Power Mirrors circuits.

E90 Power Windows Diagrams 3 E90 Power Windows Diagrams 2 E90 Power Windows Diagrams

Turns out that the power mirrors have two options, with and without a heating element, which makes a big difference in the wiring.

When I disconnected the passenger power mirror, problem disappeared. 

  • Turns out that the customer had replaced that mirror with the wrong part, a heated mirror which didn’t fit this car (even though the mirror connector fitted perfectly).
  • It caused the LIN Bus to be shirted with a power feed to the heated mirror motor, thus disabling all communication with a driver power switch also.
  • New passenger mirror fixed the problem.



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Matheus Eduardo Garbelini
Matheus Eduardo Garbelini
1 year ago

Hi Friend, can you share what part number you used that has LIN bus on the mirror?
We are trying to buy a mirror which has LIN bus instead of direct motor signal.

Alternativelly, do you know what is the internal wiring between the Mirror motor connector (8 pins) (round component) and the external mirror connector (6 pins)?

We bought a Mirror Motor connector separatally, bue we don’t know the correct pinout of the Mirror Motor connector (8 pins)

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