ABS Light On/Off

This is on a 2004 Pontiac Grand AM.

The old GM ABS light problem. The lights were on a month ago and the left front hub was replaced, the light went out. They just came back on all of a sudden (coincided with the temperature dropping to 15F). The next day they were out. Then the next day they came back on. I couldn’t get a code read with the basic scan tool.

Where should I start? I’m thinking of cleaning the speed sensor connectors and reseating with dialectic grease. Maybe they’re dirty or a bit brittle due to age and the cold?


Have you checked for a loose wheel bearing on the right front hub?


You should eventually invest in a tool that also does abs and airbag

I’ve occasionally seen them on sale at Sears, for about $200, if memory serves

It will pay for itself in the long run

Does the light stay on after you start the engine?

Or does it come on while you’re driving?

It’s quite possible the code isn’t the same one, as before

The first time it came on while I was on the expressway. The second time it came on right when the car was started. Both times it was late at night/early morning and bitterly cold. It has gone off after the car has been shut off and sitting for the night.


I have not checked the right side. The bearing on the left side was actually fine as far as making any noise or looking worn, it was just cheaper and easier to replaced it ($75) than to try and diagnose what was actually causing the issue.

Since it came on while driving, it could mean the abs module saw a problem with the signal of one of the sensors

Do you have a digital multimeter?

I don’t have one, but have been meaning to purchase one.

What would I check?

I believe you would check the ac voltage signal, while you’re spinning the tire as fast as you can, by hand

I may be wrong, but on older cars the wheel speed sensors often generated an ac signal

What you want to see is that each sensor effortlessly generates, say 500 millivolts. I don’t have the specs for your car, but that’s what I would look for. Also make sure that say, left and right front sensors have roughly the same value. what you don’t want is left front generating an 800 millivolt signal, but but the fright front only gets up to 200 millivolts

You can check the resistance of the sensors. Although it doesn’t sound like you have an open circuit

Be aware . . . many of the dirt cheap digital multimeters do NOT measure ac voltage

We had a similar issue on our 2003 Silhouette. It turned out to be tarnished or dirty contacts in a front sensor connector at the wheel. I cleaned the two front connectors and that fixed it. A good thing too because I couldn’t get at the rear connectors.


What did you do/use to clean them?

Spray contact cleaner. You can get it at the auto parts store.