ALTERNATOR VERSUS DIAGNOSTIC TESTING

[Delia Caribbean]

4.4i 2000 The battery light indicator is red. A mechanic has taken my battery to charge. Says we should then take it to his garage to get diagnostic test - then it will tell him the state of the alternator; whether it can be repaired or if it has to be exchanged.
Someone else said there's no need for the test, as the red battery light on the dashboard is telling me it's to do with the alternator. So they're telling me don't do the test, (the mechanic just wants more money) just ask him to remove the alternator and then get it checked. What do you think?

[CharlieHustleX5]

When the red battery light illuminates, that means there is a problem with the charging system. The alternator is responsible for keeping the battery charged when the engine is running. SO its safe to say that there is somehting wrong with the alternator.

I had the light go on in my 04 x5 after only 65k miles. After the red battery light went on, I took out the alternator and got it tested. It failed the alternator test. Turned out to be the voltage regulator on the alternator. The shop I took the alternator to said its common for the regulator to go out on these cars.

I think what your mechanic wants to determine is if the alternator is completely shot or if its just the voltage regulator. IMO, with your alternator being 8 years old, I would just pull it out and exchange it for another one. I'd feel more comfortable knowing I had something as new as can be and not something that has a possibility of failing on me sometime down the road.

[Delia Caribbean]

Would you say then, there's no point in doing the test as either way the alternator will have to be removed anyway?

[CharlieHustleX5]

If you haven't already charged the battery or gotten it tested to see if it's still good I would do that first. If the battery is in decent condition, then the alternator is going to be the one to change out.

[Delia Caribbean]

The battery has been charged but I've not put it in the car yet.
If I put it in the car and the red light goes off does that mean it was the battery? Or, would I have to use the vehicle for a while, and if the red light returns, that means it's definitely the alternator. Or should I just wait for the mechanic to come? Is there a way of testing the aternator without giving it a diagnostic test?

[ika]

start engine and get voltage reading by volt-metter. it must be near 13.5 . if not , alternator is demaged. I think voltage regulator is demaged. You can by aftermarket voltage regulator and replace about 100$.

[Delia Caribbean]

Thanks - got to find a voltage meter now...

[CharlieHustleX5]

If the battery is charged, the red light should turn off if the alternator is functional. If the red light still illuminates, chances are the alternator/voltage regulator is done.

[CharlieHustleX5]

Originally Posted by ika

start engine and get voltage reading by volt-metter. it must be near 13.5 . if not , alternator is demaged. I think voltage regulator is demaged. You can by aftermarket voltage regulator and replace about 100$.

The OP isn't doing the work by themselves. The difference between a new alternator and a voltage regulator replacement plus labor is minimal. With an 8 year old alternator, I suggest just replacing the whole alternator since it needs to be pulled out anyways.

[Weasel]

I have never seen the red battery light on when it was not the altenator... it's the altenator, safe bet!