E46 Battery problems

[motco]

My son has a 320TD Compact '53' reg., and it seems incapable of maintaining a charge on its battery (a new one) for more than 48 hours. Leave it three days and the battery is too low to even open the doors. He has tried switching everything off manually: radio, interior lights, climate control, but it still dies. Googling suggests a 'hedgehog' resistor in the climate control fans might be responsible but I was wondering if anyone here has any other ideas?

[miniman]

Hedgehog is almost certainly the culprit, it causes the blower fan to run on and the communications bus to stay "awake". If the car is an automatic, you'll see that the little light that shows which gear it is in will stay lit. Fortunately the hedgehog is a quick, cheap DIY fix.

[motco]

Thanks miniman. The only reason I posted the question is because he says he hasn't heard any running on of the fan. Is it possible that the bus being live might do the evil deed even if the fan is not running?

[miniman]

Yes. I never heard the fan running on my 5-series but a new hedgehog cured the problem. I think the fan actually runs so slowly it's virtually impossible to hear it.

[E30M3SE]

If you want to make sure it is the FSR then do a battery drain test with the FSR connected and then another with it disconnected.

[motco]

Thanks chaps! I don't have immediate access to the car but when he brings it over I'll do the drain test and see if the resistor is responsible. He hasn't reported any odd behaviour with the a/c but I suppose that's no guarantee it's not that. Thanks again.

[fixedwheelnut]

motco said:

Thanks chaps! I don't have immediate access to the car but when he brings it over I'll do the drain test and see if the resistor is responsible. He hasn't reported any odd behaviour with the a/c but I suppose that's no guarantee it's not that. Thanks again.

When you do the drain test open all the doors but close the latches and after connecting the ammeter let the car go to sleep approx 20 minutes, it will probably be around 80-140 milli amps until it sleeps then it should be below 40 milli amps 0.040 amps
Higher than that and you have a problem.

Then you can remove the underdash trim and unplug the resistor to see if it drops without unlocking a door and waking it up again so not having to wait another twenty minutes

Other possibles are the Auxillary cooling fan in front of the radiator or boot light/broken wiring at the tailgate hinge.

[motco]

fixedwheelnut said:

motco said:

Thanks chaps! I don't have immediate access to the car but when he brings it over I'll do the drain test and see if the resistor is responsible. He hasn't reported any odd behaviour with the a/c but I suppose that's no guarantee it's not that. Thanks again.

When you do the drain test open all the doors but close the latches and after connecting the ammeter let the car go to sleep approx 20 minutes, it will probably be around 80-140 milli amps until it sleeps then it should be below 40 milli amps 0.040 amps
Higher than that and you have a problem.

Then you can remove the underdash trim and unplug the resistor to see if it drops without unlocking a door and waking it up again so not having to wait another twenty minutes

Other possibles are the Auxillary cooling fan in front of the radiator or boot light/broken wiring at the tailgate hinge.

Thanks FWN. You sound like a chap who knows! I'll do as you suggest.