Intermittent ABS Trac lights

2001 Alero

I've read about the sensors and wiring on the hub causing the ABS and Trac lights. They come on with the Service Vehicle Soon light, sometimes, when I start rolling.

I had a mechanic look at it, and it was not giving any codes. He tried to turn off the lights with the machine, and they would not turn off. He concluded that it was a computer problem. He said that a ground causes the lights to come on, so it could be a wiring problem.

Why would my lights come on intermittently? Do I have to wait until they come on, then immediately pull over and check the sensor or hub? Is there any way to check this on my schedule?

There are a couple of possible issues here. The first issue deals with the wheel sensors that send signals to the ABS computer. The sensor will set the light and it may come on or go off depending on the issue. If the technician could not turn the lights off then there is a problem that needs to be corrected. Make sure that the computer is scanned with an ABS capable scanner.

The second issue may be a bad connector to the wheel sensor. If the connector is not making a good connection then the light will come on periodically. Check the connectors to see if they are in good shape and are fully connected. Dirt or moisture can get inside and cause the problem so you may want to pull them apart and clean them before reconnecting them.

Is there a post somewhere on here on how to get to the sensors, or do I need to buy a Haynes book? Since it is a common problem, it seems like something is probably already posted, but when I search for it, I see a thousand other posts about the problem, but no method of procedure.

The sensors themselves are an integral part of the wheel bearing assembly and cannot be serviced they must be replaced along with the bearing. The connectors should be readily accessible by raising the car on jack stands and looking at the back part of the suspension. The sensor connector should be attached to the suspension. You may also be able to access it by simply removing the wheel.

Does your light come on mostly when you are turning? If the light is intermitant, you most likley have a broken wheel speed sensor harness wire. The easiest way to tell is attatch a scanner to the vehicle and navigate to ABS/TCS data, there you will find wheel speed info. Start the car and turn the steering wheel lock to lock while watching the speed data (the front wheel speeds) they should stay at 0mph. If one or both jump around, even a very little, the harness on that side needs replaced. They run about 80.00 from a dealer and will cost about 45-50.00 per side to install. You can look at the harness and get an idea by pulling the wiring out of the conduit about 6-8" from the connector at the sensor, where the harness bends up to fasten to the control arm. If the black wrapping around the wire (not the conduit) is broken, the wire is probably broken also. It will be broken inside the insulation and will not be visible.

No, they may not come on for days - maybe a week at a time. When they come on, they usually come on when I put the car in gear. They rarely come on while I'm driving.

Sounds like I need to check wiring. Thanks for the help.

There is an Alero 2.2 gx that i am considering of buying. It also has the Service Vehicle Soon, ABS and Trac off lights on.
I drove the car and It has a really good driving. Brakes are a little tough though.
Is it a dangerous thing to drive this car while these lights are on?
Does it mean the ABS is not really working?
There is no humming or any strange noise.