Brake-light switch plausibility / pressure sensor zero deviation

The control unit for traction control checks the brake-light switch via the pressure sensor.

Possible cause(s) of fault:

• Brake-light switch incorrectly set
  
• Pressure sensor defective
  
• Cables between the pressure sensor and control unit for traction control are defective
  

Storage condition(s):

The fault is entered if the brake-light switch transmits no signal with a brake pressure greater than 15 bar.

Troubleshooting procedure:

• Slowly press the brake pedal with the engine running until the brake-light switch is activated and observe the brake pressure while doing so. Display of the brake pressure and status of brake-light switch, see Control unit functions
  
• If the brake pressure is greater than 2 bar, the brake-light switch must be adjusted.
  If this does not succeed, the pressure sensor must be replaced.
  
• If the brake pressure is less than 2 bar, the cable between the pressure sensor and control unit for traction control must be checked.
  If no fault is found in the wiring harness, you must contact the BMW hotline to find out how to proceed.
  
• Concluding test:
  Erase fault memory and carry out the following operation 3 times:
  Slowly press the brake pedal with the engine running to shortly before the position where the brake-light switch is activated Hold the brake pedal in this position for 2 seconds.
  If fault 69 Brake-light switch Plausibility and/or 72 Pressure sensor Zero deviation is then entered, you must contact the BMW hotline to find out how to proceed.
  

Note

• Which of these two faults is entered depends on the causes stated and also on circumstances such as speed of pressing the brake pedal.