Case/007

Audi A4 B8

Battery flat every two to three days

Cause: A convenience module that would not enter sleep because a door-latch microswitch was intermittently signalling the door as open.
Outcome: Latch replaced, module sleep confirmed at 18 mA after 30 minutes. No further drains.

Customer report
The customer had replaced the battery twice on advice and had been told the alternator was fine. The car would still fail to start after a weekend parked.
Initial data
No stored codes relevant to charging. Battery tested healthy and holding charge. Resting draw after 30 minutes measured at 1.2 A instead of the expected 20–40 mA.
Testing
We logged the draw over two hours to see whether it dropped or cycled. It cycled. Voltage-drop testing across the fuses pointed to the convenience circuit. Monitoring the door-status signals showed the driver's door reporting open every few minutes with the door shut.
Cause
A worn microswitch inside the driver's door latch. Each false 'open' signal woke the convenience module and the network with it.
Resolution
Latch replaced and coded. Sleep current measured at 18 mA after 30 minutes. Car left for four days and started first time.

Similarsymptoms?

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