XSeries-forum

Just beware a new battery will hide any underlying drain issue for a good while.

I know this because I changed mine only to find weeks later I had the same overnight drain issues.

The problem was the FSR...............Because the fan was only running very slightly with ignition off it was bearly aubible, thus I had totally failed to diagnose the faulty FSR & depeite being more than aware of how to diagnose.

Checking for a faulty FSR is easy.

1. Sit in car with engine running and aircon on auto

2.Turn off ignition & remove key.

3. Stay in car & activate locking with fob, then press key fob button once more immediately threafter, ( you have effectively initiated shutting things down & also deactivated the internal alarm sensors.

4. Sit for 10-15 mins and listen for faint fan noise which indicates FSR is defective.

5. Other symptoms will inlcude fan sounding erratic underpowered or as if it is labouring when on in everyday use.


It is well worth for folk to check this now as the last thing folk want in colder months is a car that wont start, (winter temps can make any drain impact battery performance more than in summer).

The failing FSRs tend to be of an older design & I dont know if BMW changed over to a newer one during the E53's life or not. Perhaps if anyone knows if this is the cae or can provide a definitive date for this they will post here.