M3 woes

[AAV]

Can anyone please offer some advice with my 04 M3, the battery warning light comes on for a split second when changing gear, "off power" this fault does not happen all the time, but always when pressing on, also the headlights will flicker occasionally.

Is this no more than adjusting the alternater belt, or leading to some thing major.

Advice would be welcome, thanks

Bob

[Neil.D]

Hvae you inspected the battery? It should have a charge indicator which will tell you if its shot. Its a little viewing hole, white means OK, black is ruined. Cant remeber exactly but the battery will tell you.

Neil

[Ollyd]

Came across this topic whilst searching for threads on E46 M3 battery warning light questions.

I have a similar issue, although I am nor not sure about the headlight flickering thing.

My battery warning light has started to flicker on and off for a split second. It seems to be getting worse too, with the light staying on for longer periods now (up to 10 seconds at a time).

I find that if I accelerate it goes off and it comes on when I break. This is not always the case but a trend. Might this be just a loose connection or are we talking more extortionate bills from my friendly dealer?

Interestingly I took the car in for this issue a couple of months ago but as usual they could not find any fault logged on the computer and could not replicate the failure mode. The car is now just off warranty so who wants to bet that they will find an very expensive problem now!

Any ideas or hints appreciated.

[Mroad]

Your problem sounds like the alternator or battery but most likely the alternator (or part of it's circuit).
Check the battery voltage with the engine running, it should be roughly a steady 14v, anything less (below 13.5v) or wildly erratic and the alternator is not supplying the correct voltage and will need checking. It could be as simple as the alternator belt slipping because it's loose (at higher revs the belt becomes taut and drives the alternator, dropping the revs and the belt slips) or it could be a loose earth lead, these two will be the cheaper fixes. It could however be the voltage regulator on the alternator has failed and it's not supplying the full 14v it should.
If it is the alternator and you don't want to go to the stealers (who will just replace the alternator if it's faulty) you can go to an Auto Electrican who may be able to replace the voltage regulator for you or at least fit a refurbished unit (check the price against the stealers though).

It's best to get this sorted as soon as possible as the battery can be damaged or certainly it's life shortened by excessive drainage.