Accidentally revd my car on a cold start this morning and the battery light turned on

[TridentVibes]

Hey all,

So I did something pretty stupid today - This morning when I turned on my car (2002 530i with about 170k miles), I was adjusting my seat cover and as I was lifting myself up, my right leg extended and I accidentally rev'd my car to nearly the redline and the battery light indicator turned on. lol...

And after googling around, the light means "there's a malfunction in the alternator v-belt or in the charging circuit of the alternator". Now my knowledge of cars isn't the greatest, but I do know the basics, so I do know that the alternator is used to provide charge for the battery, so I decided to just drive to work with the hoping the alternator would correct itself by just charging the battery.

When I'm applying gas and accelerating, the battery light turns off, but the moment I release the gas pedal, the battery light turns back on. I even drove on the highway for about 15 miles and same results.

The car doesn't feel 'sluggish' or like it's about to die or anything. What could be wrong?

Also, the battery was changed last year, and I believe the alternator was replaced 2-3 years ago (recent hand-me-down car, so I don't know the exact timeline).

[JimLev]

I hope you opened the hood to make sure the serptine belt wasn't loose.
If it was broken you'd be overheating too.
Possibly your alternator or the brushes are shot.

[StephenVA]

The Battery light indicates that the CHARGING system is not functioning correctly. Belt, alternator itself (Bushes, regulator, windings, grounds, wiring, etc)
Test system, don't guess
If you have limited DIY skills as you mentioned the you need to see any independent competent BMW repair shop for assistance. Charging system should put out 200+ Amps and 14.0 volts at 2500 rpm

You will only see a difference when the battery runs out of voltage due to not being recharged by the charging system. Basic Automotive 101

[jclausen]

I would check the belt maybe it got cooked and is slipping

[CPHES]

If the belt is still attached ( If the steering is ok, and he does not overheat, then the belt is likely ok ), the I vote you dig into the alternator / voltage regulator, but you are on borrowed time, and revving in the cold was not the only factor in this.

[ross1]

If the alt belt on this engine broke you also lose steering assist and the water pump. Hard to steer? Don't drive it.

[TridentVibes]

Thanks for all the advice thus far, guys.

Sorry for the late response - was at work pretty much all day - but I checked the serpentine belt and it looks good; Doesn't look like it's slipped out or anything and the power steering is working fine and the car isn't overheating either.

It's a little late now, but I'll check the alternator and battery in the morning. though i'm not exactly should what i should be checking for, but I'll google around.

[JimLev]

Does your alt light come on at idle?
Read the battery voltage at idle speed when the engine is hot.
Then rev it to 2K RPM and see what it reads.

[geargrinder]

Sounds like classic case of altertater early death symptoms.

[GotF1]

Sounds like classic case of altertater early death symptoms.

Ageed! Mine recently dies while pulling into my driveway. Didn't know why and long story short, I kept trying to start it but the alternator siezed and the fried the starter. Replaced the alternator pretty easily then the starter killed me for 8 hours while trying to get the top bolt off. Ugh! Lessons learned...

[TridentVibes]

Reporting back -

So the battery reads 12v at car off
Idle reads 11.5v
Revd to 2.5-3k reads 11.5v

And the alt light stays on during idle but when the car is revd passed 2k, then the light turns off

[atobe]

11.5V with car on means your alternator is not working. Don't drive the car until it's replaced, unless you want to be stuck somewhere.

[StephenVA]

+1

[Chedley]

+1
Replace the alternator asap, and recharge your battery to full. It should then read 12.6 v with engine off.

[TridentVibes]

Got it, working on it now.

Also when you say recharge the battery to full, you mean just drive the car for a bit after the alternator is replaced to charge it, right?

[edjack]

No, he means to hook it up to a charger at a 6-10 A rate for 24 hours.

If you don't have one, Harbor Freight has a selection. Get a smart one.

[djb2]

You are going to need to pull your alternator and check the brush length. New is 13mm, minimum is 5mm.