ABS light turned on

Hi,

Chances are one of the wheel speed sensors has failed. If it does, the light will come on. One other thought is this. If the brake fluid in the master cylinder is too low, it can cause this light as well, so check that too.

Now, the wheel speed sensors are behind each of the brake backing plates (behind the brakes). I attached a pic below showing the locations for the left and right front.

What you need to do is check to see if they produce a voltage signal when the wheel is turned by hand. Here is a link that explains how it is done:

https://www.2carpros.com/articles/abs-wheel-speed-sensor-test

Let me know if you are comfortable doing this or if you have other questions.

Take care,

Joe

See pic below.

Are there only the two front sensors?

Hello, I'm Danny.

Just here to add my two cents. The best thing for you to do first is perform a CAN scan. A CAN- Controller Area Network scan will test and retrieve all codes that are stored in your vehicles computer when your malfunction light is on. This scan will test all systems on your vehicle including the ABS- anti lock brake system you mentioned. Here is a tutorial showing how to perform this scan:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

After you perform this scan get back to us with any fault codes and we can then properly diagnose the issues your brake system might be having on your GMC. Hope this helps and thanks for using 2CarPros.

I do not have a scanner.

I checked drivers and passenger side, both have the 1000-1300 ohms resistance.

Only the passenger side when set to AC and the wheel is turned does anything on the voltmeter. Drivers does nothing. I tested this twice on two different days.

I changed the drivers abs sensor today... did the ohms test and that worked but when I tried the A/C and turning the wheel nothing.

Got in and drove it around to heat up the bearing... not that would make any difference and drove for about 10 highway and still the light is on.

By any chance, were you able to scan the controller area network (CAN)? Also, please reconfirm something for me. Do I understand correctly that the only time you get a signal from the ABS sensors is when the AC is off? If the AC is on and you turn the wheel, do you lose signal?

Joe

I am not a mechanic that has a scan tool.

When I mean AC - I am talking about the voltage that is generated by spinning the wheel.

I have a cheap voltmeter - if I set it to 200 on AC on the passenger wheel it will go up to 6 if I spin the wheel fast.

If I go to the divers side , hook it up the same and passenger with same setting on the voltmeter it does not read anything when I spin the wheel.

Seems rather ODD to me but again I am not mechanic.

This car has never had an ABS light issue. It just came on one day out of the blue when I put the car into drive moving it in my drive way.

Hello again.

As we stated before regardless of how well your vehicle is running-driving but by having the ABS light come on that means a fault code is stored in your vehicles computer. Performing the CAN scan we mentioned can help us determine-diagnose what is wrong and why the code is set. You mentioned you don't have a code reader but some parts store like AutoZone will do this scan for free. Hope this helps and thanks again for using 2CarPros.

Danny-

Sorry no AutoZone in my area... I guess I will try to get my hands on scan tool.

However, if the new sensor is installed and I connect a voltmeter at a minimum should I not be able to get a voltage reading...
that in of itself does not require a scan tool... right?

You are correct. Are you sure the toner ring isn't corroded in dirt and grease, damaged or loose? If the sensor is new, you are testing right at the new wiring to the sensor, so you should be getting a signal.

Remove the sensor and do your best to look down into where it mounts. Check if the toothed toner ring is clogged with dirt, if it is damaged, or if it is disconnected and not moving. It has to be one of them causing no signal unless you got a bad sensor.

Let me know.

Joe

Hello again.

I've attached an anti lock brake system wiring diagram below in case you want to test the wiring circuits to which the wheel sensors are located. Here is a tutorial showing how to test electrical wiring:

https://www.2carpros.com/articles/how-to-check-wiring

Keep us updated to if you ever get the code information on your vehicle. I've cut the diagram into three pieces so you can view larger. Hope this helps and thanks again for using 2CarPros.

Danny-