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.

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.