Warning Lights While Driving

I have a 2002 Buick Rendezvous with 25,000 miles.
While waiting at a traffic light with low rpm, the dash warning lights come on momentarily and then go off. Specifically, the battery light, seat belt light, and others which I cannot remember. The vehicle has the original battery.
I am thinking dying battery or alternator. Are there other ideas?

 

Does sound like a weak battery, but go to a local Autozone type store and have them do a basic alternator/battery check for you. They will do this for free.

 

Doesn't sound like a weak battery to me, although it's quite possibly half wrecked by now because of the underlying problem.

Battery light indicates a charging system problem (alternator), the low rpm comment pretty much seals it. Those diodes don't all go out at once so it's probably just generating less power than it used to but still functioning.

Honestly, I wish they never called that idiot light a "battery light" to begin with. Battery charge system light or alternator light would have been better choices.

 

Well, usually a failing alternator throws up the battery AND brake light.

 

I wonder if the car simply isn't kicking out electrically and immediately restarting. I would check the battery cables. Clean both ends of each cable.

 

Might be a BCM (Body Control Module). I'm willing to bet that if this thing was scanned for DTC's, there would be many. We get these things in the shop all the time for problems that the BCM causes.

If you get it scanned for DTC's, make sure they can check every module in the vehicle. May have to go to the dealer to get this done. If it happens to be the BCM, it is not a DIY repair, the dealer has to do it unless you know an independent shop with TIS and Dealer World access for programming purposes.

 

Thanks everyone for the helpful ideas.

 

Could be failing battery or alternator
It's a little early for alt failure, and it could be time for a new bat if you have harsh winters (not sure how cold ten gets)
These can both be checked at a DIY parts place, usually at no charge

But still...first I'd check for a loose belt, make sure that's up to specs
A slightly loose belt will allow the alt to work fine at higher engine speed, but slip at a lower one



Good thing I had my Alpha-bits for breakfast this morning

 

I checked the the battery eye and it is dark. I think I need a new battery. I guess I need to find out if the alternator is charging.

How much "stuff" do I need to take loose/remove to change out the battery?

 

That's exactly what you need to do. And that does not involve removing the battery nor purchasing a new one. But it wouldn't be a idea _after_ you determine what the problem is.

Any cheap voltmeter will tell you, or you can take it to the auto parts store for a free test, as others have said.

Or you can run right off to the store and buy a brand new battery like so many people seem to do, have a working car and think you fixed it, and then be facing the same situation in a month due to chronic undercharging.

 

Thank you, Core.

I have a digital multimeter which will read dc volts. Where do I place the probes to check the alternator output?

I am not experienced in auto electrical stuff beyond replacing a bulb or a battery; but this vehicle has a fender brace and apparently the fuse block in the way where the batttery would have to come out. That is why I was asking in my previous post what steps would be involved once I disconnect the battery cables.

 

I doubt taking a meter to the alt will do much. You could still have 13.5-14.5 volts, what really matters is the amps, and you need a ammeter for that.

The alternator also needs to be under load to get a accurate test done.

I'de say replace the battery, it's over 5 yrs old already! Get the battery at Autozone, they will put the battery in for free.

 

This is a good starting point, although I do agree with what Mark just said.

Start the car and leave it at a normal idle. All accessories such as lights and blower off. Measure the voltage at the battery posts. It should be at least around 13.7V. If it is much lower than that then the alternator is not delivering the juice. Which could caused by a bad diode in the alternator OR the belt problem already mentioned above.

Under no circumstances remove the battery cables while the car is running. The only reason you should remove the battery cables is to clean them, which hopefully you have already done.

Repeat the test with the lights on high beam.

You might also have a friend rev up the engine to 1500 rpms and repeat your voltage readings. If the idle voltage was low (say 12.50) but immediately and suddenly jumped up to 13.7+ at certain rpms, that would lead me to believe the belt was slipping.

While you're out there, also measure the battery voltage with the car off. I know it's going to be low because the battery has not been being charged properly, just curious to know how low. You might also compare this with the reading you get after some decent highway driving. Again not important just curious.

-core

Edit: Although it may be time for a new battery, replacing it may not (I'd say likely not) solve the underlying issue. Even though everything may appear fine right away. After a while of repeated undercharging he'll be left with another wrecked / partially-sulfated battery.

 

It was the battery. Got a new one installed today. It was a pain, but the Autozone guy got it done. Thanks, guys.

 

Sweet! Glad to hear thats all it was.