I recently baught a 2003 545 and it started randomly putting the hazards on, unlocking the Doors and turns off the fuel pump. Its like it thinks its had an accident, but then i can just start the car again and it will be fine for a few days. There is a fault that the bst has had a firing attempt ( fault 99b01 and 99b06) also have faults 991b and 991d. Any ideas what could be causing this ?

 

The cars do all sorts of strange things when the battery isn't solid. If the BST is wonky, you should replace it. Perhaps there is some intermittent issue there causing your issues.

 

Check your battery, read the DTC codes.

 

battery voltage too low. Measure when running. Should read something like 13.4 <> 14.5 volt at least. If below 13.4 either the voltage regulator or the the dynamo is gone. typically with a too high voltage when running the regulator is gone and thats dangerous as well as due to the high charging voltage the battery will generate hydrogen. When too low normally the brushes of the dynamo are gone.
Then measure the actual current when the car is switched off after 15 minutes or so. If modules are faulty they could drain the battery. Check the faultcodes with Ista as well to find the culprit.
After one night of not running. Measure the battery voltage (at the battery...NOT under the hood). Should ready minimum 12 or 12.5 volt. Anything below that is a big chance the battery is gone.
Check the IBS as well (at the battery in the rear).
If you replace the battery do all of the above first because a new battery can be gone in one night.

Hope that helps......

reg

willem

 

Check this vid.....