2004 Venture Over Charging?

RITT

MEMBER
2004 CHEVROLET VENTURE
133,000 MILES

Have a 2004 Chevy Venture van 3.4L V6 with 133000 miles. The battery light comes on after running for 45 min or so on idle and about 20 min if driving. The light is never on in the morning when you start the van. I have checked all the cables cleaned and replaced the battery. I had the alternator tested at AutoZone and it is good. I used a digital meter when the lights started flickering and the car started to act funny. The alternator seems to push up to 18 or 19 volts when this happens. Also when you idle up the car it jumps up again. I don’t believe that it should jump that much when you idle it up to 2000 rpm. The jump only seems to come and go but the battery light after it comes on stays on until cool down. Alternator works fine most of the time pushing 14.3 volts on the meter even when the light is on. Any help would be great. Thanks

5 Replies

JACOBANDNICKOLAS

MECHANIC
108,164 POSTS

It sounds like the voltage regulator is bad. Have that checked.

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Thursday, March 8th, 2012 AT 10:43 PM

RITT

MEMBER
3 POSTS

The regulator is built in to the alternator.

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Thursday, March 8th, 2012 AT 10:52 PM

JACOBANDNICKOLAS

MECHANIC
108,164 POSTS

That is correct.

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Thursday, March 8th, 2012 AT 10:56 PM

RITT

MEMBER
3 POSTS

So would you suggest that I replace the Alternator? Don’t know anyone that will test the regulator without paying a bunch. A good new Alternator is about $250. It would probably cost half that to have it tested. I will check around thanks for your reply.

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Thursday, March 8th, 2012 AT 11:56 PM

CARADIODOC

MECHANIC
33,737 POSTS

Hi guys. Excuse the interruption. As soon as you see that 18 and 19 volts, you know the voltage regulator is shorting intermittently. They are extremely difficult to get out without causing damage to the diode block. By the time you're done buying replacement parts you can have $100.00 in it not including the time and tools needed to do the repair. Look around for a rebuilt unit with a good warranty. My friend found one with a one-year warranty for just under $200.00 for his car, and another one with a lifetime warranty for around $150.00.

What you must be aware of though is due to the design of these generators, (they switch the field on and off about 400 times per second), is that field coil acts just like an ignition coil and creates huge voltage spikes. Those spikes take out the internal diodes, voltage regulator, and they can interfere with computer sensor signals and cause hard-to-diagnose running problems. It is real common to go through four to six replacement generators in the life of the vehicle. The way to reduce the number of repeat failures is to replace the perfectly good battery at the same time. As they age, they lose their ability to dampen and absorb those spikes. The old battery will work perfectly fine in a 1986 or older GM vehicle that still had the really good generators.

If your battery is less than two years old you shouldn't have to replace it.