Check charge system message

I just had AutoZone check the alternator and it's fine. The battery light came on again very briefly but not the "check charging system" message. I realized it comes on only when I speed up while getting on the highway.

Hello,

This might be a problem with the vehicle's serpentine belt. Check to make sure that the belt is tight and not glazed and all the ribs are there. I have included a few links for you to go to below:

https://www.2carpros.com/articles/how-a-serpentine-belt-works
https://www.2carpros.com/articles/how-a-serpentine-belt-tensioner-works
https://www.2carpros.com/articles/replace-serpentine-belt

Please go through these guides and get back to us with what you find out.

Thanks,
Alex
2CarPros

Also be aware GM has had a real big problem with repeat generator failures since they redesigned them for the '87 model year. They develop huge voltage spikes that can damage the internal diodes and voltage regulator, and interfere with computer sensor signals. The battery is the key component in damping and absorbing those harmful spikes, but as they age and the lead flakes off the plates, they lose their ability to do that. Any time you replace a generator on an '87 or newer model GM product, to reduce the high number of repeat failures, always replace the battery at the same time unless it is less than about two years old. The old battery will work fine in an '86 or older model.

I looked at the belt. On one edge it's very slightly frayed. Not totally flat like the other side. It doesn't look like anything major to me but I'm not a mechanic. I'm curious to know, if it's the belt what causes the light to go on only when I first get on the highway.

Hello again,

It's very possible. A loose or worn serpentine belt will cause the alternator output to be lower than normal and will really show when the vehicle's engine is accelerating or under a load. Here is a link below on how to properly check your vehicle's serpentine belt:

https://www.2carpros.com/articles/how-a-serpentine-belt-works

Please go through this guide and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros

I had my mechanic put another belt on. It took me a while to test it out anywhere where I could drive at high speeds due to the fact that I badly needed two new tires. I just got them and was on the highway. Once I reached 60 mph the battery light came on again. As soon as I took my foot off the accelerator, it went off. When I was on another road, as soon as I hit 50 mph it went on again. It seems like, only at high speeds, if I slowly accelerator it doesn't seem to go on. But when I really put my foot on the gas, that is when the light goes on.

Hello again,

Okay, this could be a problem with the serpentine belt tensioner. In the diagrams down below I have included the factory guidelines for testing and inspection of your vehicle's serpentine belt tensioner. Please go through the guide and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros

According to my mechanic, when he changed the belt he also checked the tensioner and it was fine. As for what Caradiodoc said, the battery isn't old. It was bought new a couple of months before my son bought the car which wasn't too long ago.

Yesterday, when I was driving, the light was going coming on when I reached 40 mph. It was when I was creeping up to that speed. I didn't even really have my foot on the gas that much so it seems like it's getting worse. What else could this possibly be? It's driving me crazy. I really do appreciate the suggestions.

I just want to add that we had no problem with the battery light coming on until we had a new alternator put in. The alternator, belt and tensioner are all fine.

Forgot to mention that yesterday the service engine soon light came on, but I don't know if that has anything to do with this.

Hello again,

If your vehicle's Malfunction Indicator Lamp (MIL) or "check engine" light is illuminated could you please pull the Direct Trouble Code(s)(DTC)(s) for us. Here is a link for you to go to if you are unfamiliar with how to do this, and you will need a code reader to do this:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please go through this guide, if necessary, and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros

I went to AutoZone to get the code. It's P0420. From what I'm told now I need a new catalytic converter which would not cause the battery light to come on. Is that right?

I realized today when I first left, I made it up to 50 mph and the battery light didn't come on. I didn't stay at that speed. I was just able to briefly test it out. I drove about 15 minutes away on city roads, so within 35 mph I was going. No problems until I was coming home. I was at 30 mph and the battery light came on. All other times, once I would take my foot off the gas the light would go off. This time that didn't happen. I was able to just keep my foot off the gas and waited about 30 seconds to a minute for it to finally go off. It definitely seems like it's getting worse.

I have seen the instrument cluster cause this problem. here is a wiring diagram to show you how the system works and a video that how the cluster being replaced in a similar car:

https://youtu.be/_HEC44xENxw

Check out the diagrams (Below). Please let us know what happens.

Thank you Ken, but I'm a little confused. I'm not having any problems with the gauges since they put in the new alternator. It's just the battery light.

Can we check to see if the alternator is working? here is a guide. The battery light is run through the cluster and can go bad leaving the battery light on.

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Please run down this guide and report back.