Ground under drivers feet?

[linneje]

I remember reading somewhere that the brake system has a ground under the drivers feet. I have an intermittent ABS light and I would like to check/clean up this ground. Is this on the underside of the long wheelbase GMT? Has anyone ever cleaned up this ground. Where exactly is it located?

I have checked the thread with all of the ground locations but I can't seem to identify the correct location.

 

[HARDTRAILZ]

Intrigued. I don't know of this ground location.

Every intermittent ABS I recall is from SWPS or bad hub.

 

[Mooseman]

FAQ is your friend.
Electrical Ground locations

To properly diagnose though, you should try to pull the error code from the ABS.

 

[Capote]

I remember reading somewhere that the brake system has a ground under the drivers feet. I have an intermittent ABS light and I would like to check/clean up this ground. Is this on the underside of the long wheelbase GMT? Has anyone ever cleaned up this ground. Where exactly is it located?

I have checked the thread with all of the ground locations but I can't seem to identify the correct location.

This can also be a symptom of your ignition switch going bad. The last one I had to go bad, gave me a false ABS light.

 

[linneje]

I had a chance to scan the vehicle, and it has history codes for Left Wheel Speed and Right Wheel Speed missing, and also one about ABS relay circuit open. Sorry I did not write down the numbers (really couldn't find a pen???)
When I did a quick drive in the parking lot, even at idle the Left and Right Wheel Speeds were 3. They do not change when driving. So I asked to monitor the rear wheel speed. It was also at 3, even when driving.
The ABS indicator light on the dash will sometimes disappear and reappear as I drive. The ABS will occasionally activate if I am braking and the ABS light happens to be off at that instant.
Since both wheel speed sensors are affected, I am thinking that it is definitely a ground problem. But could a faulty relay be ruled out?
I am going to put it on a hoist to do an oil change today or tomorrow, so it is time to try to get at it.

 

[Mooseman]

It's normal for the speed sensors to show a low number while stopped. If they don't change while moving, that's another story. Does your speedometer work?

 

[linneje]

Yes, the speedometer does work. From reading in a manual I see that the ABS system tests above 11mph, and then the lamp will either go out or stay illuminated if there was a problem before. So I will have to do another drive test going a little faster, and check the wheel speed output. I can get my daughter to drive while I watch the scanner this time.

 

[linneje]

Okay, I did find the ground. It is on the outside of the frame rail, and I was looking on the inside.....
I cleared the history codes, cleaned and polished the ground. On a test drive, the wheel speed was at 3mph at idle. Then after getting up to about 10 or 11, the wheel speeds started to display. I had all three (LF,RF, and rear) speeds. They matched. However, I think I saw the left front disappear very briefly once or twice. There was a current code after the test drive, indicating only the LF wheel speed circuit.

So I think there was a bit of a ground issue. But now I think the problem with the ABS light is in the LF wheel speed sensor. I am going to drive it for a bit before checking the code history again to see if the problem is limited to the LF sensor. This would obviously be a lot easier to fix/troubleshoot if it is only that sensor.

 

[Mooseman]

That or the hub or sensor is on it way out. Usual failure is ABS activation at low speed for no reason. Hub failure is the reason for that one.

 

[linneje]

I have driven it for a week, now I have checked the codes again. Only codes for the left wheel speed sensor. Current code is left speed sensor circuit shorted or open, history codes involve speed signal erratic or missing. So I believe the replacement of the hub is my next logical step ... see if that will eliminate the ABS light.

 

[16vcabman]

rust under the sensors can cause the abs to come on at low speeds too. I know the depth of the sensor is real critical to these beasts.

 

[linneje]

Good to know. I will trouble shoot a little more to see if I have any loose connections when I get a holiday. The ABS light will disappear occaisonally so perhaps I can move some wires with someone watching the ABS light to see if I can get it to blink on/off with a particular wire or connector.