Does my Z4 need a new alternator?

[ben g]

When I bought my Z4 almost 4 years ago now, the red battery light appeared on the dash on the test drive. Didn't really worry about it too much as when I drove the car away, the light didn't re-appear.

Over my ownership, i have experience the same red battery light come on, under cold start up's. It probably does it once a month or so, more so in colder weather.

I've also noticed that when I'm stationery and turn my steering wheel left to right and visa versa, my headlights dim slightly until I stop turning the wheels. They then return to full brightness.

Is this a sign of an old alternator needing replacement?

I've changed the battery for a Bosch S4 a couple of years ago and the drive belts are all new, as is the starter motor, so I highly doubt it's any of those.

 

[Smartbear]

If your alternator needed replacing Ben your battery would be going flat, it sounds as though the change warning light circuit maybe going faulty.
You need to put a meter across the battery terminals to measure the voltage when running.
Regards

 

[fixit man]

Hi,

Could be the alternator, could also be the battery, seems like the battery is not fully charged with your lights dimming under load.

Try charging the battery overnight and try it again, if it's better this may indicate that the Alternator is not keeping the battery fully charged and get your Alternator tested with a voltmeter !

 

[Fastatv]

When the car is not moving, and you turn the steering, that will require more energy from the charging system due to the electric steering, and I'm guessing your engine was at idle RPM, that can dim the headlights a bit......even applying the brakes ( brake lights ) or turning on the heater/ac fan...all can dim headlights at an idle. You may very well have an issue with the alternator, but apparently you have had the issue for about four years ( so it's been good to you ). The only way to correctly verify the function is by testing but....sounds to me that the only issue is that it should charge slightly higher at lower RPMs. So, what I'm suggesting is that it's probably not a perfectly functioning alternator but hey, it's worked fairly well for four years..

 

[SamUK]

My alternator died in my Alpina..

battery was also near dead..where if the car was snot used for a week the battery would go flat...however when i jumped it..and drove battery would charge up.

so when my alternator packed up...

I diagnosed the issue - i charged the battery fully using a charger, started the car - as soon as i tuned the wheel left and right the battery light would come on..and the car would near switch off and battery would be flat..

The power steering is electric, and the alternator is meant to power this once the car is running but it was not.


also check youtube..you can get a volt meter to get readings from the battery with car off \ on \ and with fans lights etc on..to see what is being supplied to it from the alternator.

 

[Ewazix]

It's always worth checking that the battery, alternator and chassis earth connections are all good first.
Once done the basic DIY test of battery & alternator with a volt meter involves measuring over the battery +/- terminals without the engine running looking for about 12.4 ish Volts (good battery).
Then with the engine running and electrical accessories OFF a healthy alternator should be giving around 13.7v - 14.5v. Stick a load of accessories on then see if the voltage drops below 13V, if so the alternator is functioning but marginal and may be on it's way out.