This BMW 420d Convertible (F33) came to me with an intermittent convertible roof fault.

The roof would sometimes operate normally, but at other times it refused to open or close, making the fault difficult to reproduce.

Using in-depth diagnostics and analysing the live data, I discovered the passenger-side rear window position signal was intermittently dropping out of specification. Although the rear window itself was operating correctly, the roof control module couldn’t reliably determine the window’s position, preventing the roof from operating as a safety precaution.

Further investigation revealed the real cause of the problem.
On removing the rear quarter trim, I found the compartment completely full of water, leaving the rear window motor partially submerged. The water ingress had been caused by blocked convertible roof drainage channels, which had allowed water to build up inside the vehicle.

The repair included:
  • In-depth diagnostic assessment using live data
  • Fault traced to the passenger-side rear window position signal
  • Blocked roof drainage channels cleared
  • Water removed from the rear quarter panel
  • Rear window motor replaced
  • Electrical connectors cleaned and treated
  • Full operational testing carried out to confirm the roof and windows were working correctly
This is another great example of why accurate diagnosis is so important. An intermittent electrical fault could easily have led to unnecessary parts being replaced, but by identifying the root cause, the issue was repaired properly and the customer avoided further water damage.

If your convertible roof is playing up, you have an intermittent electrical fault, or your vehicle has a problem that other garages can’t seem to diagnose, get in touch. I provide professional mobile diagnostics, servicing and repairs across Huntingdonshire and the surrounding areas.

#BMW #BMW420d #BMWF33 #Convertible #ConvertibleRoof VehicleDiagnostics ElectricalFaults MobileMechanic CarRepair BMWSpecialist Huntingdonshire Huntingdon AlconburyWeald KeepingYouMoving