Unintended ABS activation at low speeds

FriendlyMan · February 14, 2014

Year 2000 Chevy Silverado 1500 4.8L V8, standard transmission

I have the dreaded ABS activation when I am braking below 5-10mph. Usually no ABS light comes on; however, it has come on before, along with the brake light, but it turns off the next time I start the truck. This is rare though, most of the time there is no ABS light or no check engine light.

Yesterday two new TIMKIN hub assemblies came in with sensors included and I replaced both front hubs. The problem still persists. Anyone have any ideas on what I should try next? I think this weekend I will try to check the connections and ground wires.

I have read there is another sensor in the rear diff, but there is an internet consensus that its extraordinarily unlikely that its the cause of the problem--though IDK.

The symptoms I have are identical to http://www.duramaxforum.com/forum/drivetrain/145570-abs-activates-when-braking-low-speed-2.html but I have tried his solution and so far it has not worked.

nht mike · February 14, 2014

I had the same problem on my '94 GMC with the rear wheel antilock and it turned out to be the speed sensor for the speedometer. If you watched the speedometer sometimes the needle would just drop to 0 from about 5 MPH then go into antilock.

On that truck there is a harness plug behind the glove box where you can access the speed sensor wires.

Mike

2017SierraSLT · February 14, 2014

Pull the fuse for the ABS system, and see how the brakes work. 99 percent of the time, the front hub sensors are the culprit.

FriendlyMan · February 14, 2014

Pull the fuse for the ABS system, and see how the brakes work. 99 percent of the time, the front hub sensors are the culprit.

I had taken the ABS fuse out when trying to diagnose the problem and it drove normal again except the abs lights then come on. I have since put the fuse back in and replaced both front hubs and sensors and still have he same problem.

FriendlyMan · February 14, 2014

I had the same problem on my '94 GMC with the rear wheel antilock and it turned out to be the speed sensor for the speedometer. If you watched the speedometer sometimes the needle would just drop to 0 from about 5 MPH then go into antilock.

On that truck there is a harness plug behind the glove box where you can access the speed sensor wires.

Mike

The spedometer sensor isnt too expensive and I could replace it. Is there any way to test it though? Any deas where it is on a standard transmission truck?

EDIT: Here it is at Autozone http://www.autozone.com/autozone/parts/Duralast-Vehicle-Transmission-Speed-Sensor/2000-Chevrolet-Silverado-1500-2WD/_/N-jep0eZ9gsum?itemIdentifier=195823_676146_20285_

I suppose it couldn't hurt to try and clean it before I buy a new one. I will try it some time this weekend and report back.

nht mike · February 14, 2014

My '94 was a c1500 4X2 with the optional NV4500hd transmission.On it the sensor was in the tail shaft near the driveline u-joint. There is an ohm spec for the sensor and it can be checked at the sensor or at the plug under the dash. The '94 had an older dash so it needed something called a "drac" that changed the sensor signal from analog to digital and it can also go haywire, but I don't think your dash has that.

You could also go to your local parts store and hook up to your OBD2 conector and it should give you some hints on where to look.

If your local libary is like ours you can go to their web site, use "advanced search" and have access to automotive manuals.

Mike

FriendlyMan · February 16, 2014

Hey just to follow up I went to the auto store and replaced the speedometer sensor. http://shop.advanceautoparts.com/webapp/wcs/stores/servlet/product_vehicle-speed-sensor-bwd_20971597-p?searchTerm=speed+sensor

This fixed the problem, there is no more low speed ABS activation. First I cleaned the wires and connections on all the wires and drove around a little bit and that's when I noticed the speedometer was jumping around and didn't register a speed increase until about 5mph. Thank you NHT Mike for pointing that out.

The old one had lots of metal shavings on and around it. That makes me a bit nervous, any suggestions on cleaning that out?

lunytnz · March 22, 2014

Just want to thank you guys for this helpful thread and the links to related info. It was great to find so much info on this weird behavior. I read elsewhere that there might be a recall item for the wheel speed sensors, but the dealer I called so 'No' (on my 99, anyway). I will watch the speedo closer to see if it's doing anything weird below 5-10 MPH.

I read something about it being tough to get the sensors out of the hub if they are rusted too much... anyone have tips on getting them out? Any pics? Does the wheel/tire have to come off to get to the sensor?