ABS activates at low speeds?

[inh]

Bare with me guys, I'm in Iraq at the moment, and cant get on the chat to ask the regulars...

My wife said one time while backing out of a parking spot, she stepped on the brakes, and from what she describes to me the ABS activated for some reason. Another time it happened as she was leaving a parking lot..

She said she noticed the ABS light was on earlier today, but after the ABS incident in the parking lot it went out. I told her to keep an eye on things and will update this thread accordingly...

Already replaced the rear diff sensor, as the ABS light was on awhile ago, and this fixed it.. until now... dun dun DUNNNN!!!

Any ideas guys? I know I need to take it to a real auto shop to have the codes read and see whats up, but I'd like to diagnose it further...

 

[Carguy3J]

Likely to be one or both of the front sensor(s) / hubs. If it is, plan on a hub, as it is nearly impossible to get a sensor out of the hub without it (the sensor) breking in half and getting stuck in the hub. Also, a failing hub could cause the ABS problem, as metal shavings floating around in there are not going to make the magnetic pickup, in the sensor, very happy.

For some strange reason, I actually had both front ABS sensor WIRES get cut on my Explorer, within a few weeks of each other. Don't know how it happened, but they looked like they somehow got caught in the suspension and crushed.

 

[markcoronado]

I had the same problem on my 95 EB.
The abs would kick in every time the vehicle was almost stopped.
No light on the dash.
It ended up being the right front abs sensor.
Kind of expensive since it's part of the front bearing assy.

 

[inh]

Yay new hubs =/ I guess it'll make for at least one, maybe two trail spares!

I'm with you guys on the thinking though. A couple weeks back we were out romping in the desert, could very well be dirty.. If problems continue I'll have my dad look at it and try to clean the sensors. After that, get the codes pulled to determine which hub is being problematic, and then replace it.

 

[Carguy3J]

There's nothing to clean. The sensor is bolted to, and sits inside, what is supposed to be a sealed hub/bearing assembly. If the sensor need any cleaning, then the bearings are contaminated too, and the hub needs to go anyway.

 

[inh]

Ah ok, been a long time since I've looked at the front hubs in any serious way. I replaced the front shocks a week or two ago while I was home on leave and thought I might have gotten some crud in there. If i recall correctly the tone ring is visible outside, so I can see how it could have gotten dirty...

 

[Carguy3J]

Wait a minute..... Are we talking about a 2wd or 4wd? 2nd Gen right? If you have a 4wd 2nd gen, then there is no exposed tone ring, it's sealed in the hub. If it's a 2wd, then I'm not too familiar with that setup. In that case, forget what I said about sealed hubs,etc... I do know the 2wd has "conventional" style wheel bearings, and, I'm assuming, an "external" ABS sensor and tone ring (part of the CV Axle). This style could be subject to contamination which might be able to be cleaned.

 

[inh]

Ya know, I own a 2wd and 4wd, and am probably thinking about the 2wd hub even though the issue is on the 4wd... Thanks!

 

[Elessar65]

I occasionally have the same abs issue with my 98 Sport. Every now and then if I am turning and stopping, like pulling into a parking spot, the abs will kick in. Its only done it since I went to larger tires and installed a locker in my rear diff. I figured it was the sensor in the rear not liking it when the diff locks and it thinks the wheels should be turning at different speeds. Never had a light or anything come on though. Its a minor annoyance though, so I just let it go.

 

[Carguy3J]

I occasionally have the same abs issue with my 98 Sport. Every now and then if I am turning and stopping, like pulling into a parking spot, the abs will kick in. Its only done it since I went to larger tires and installed a locker in my rear diff. I figured it was the sensor in the rear not liking it when the diff locks and it thinks the wheels should be turning at different speeds. Never had a light or anything come on though. Its a minor annoyance though, so I just let it go.

"Its only done it since I went to larger tires and installed a locker in my rear diff. I figured it was the sensor in the rear not liking it when the diff locks and it thinks the wheels should be turning at different speeds. "

Bingo. You answered your own question. This is exactly why you need a tuner/programmer to correct tire size and/or gear ratio changes. Of course, there is no way to tell the computer about the locker, but I don't think that should be an issue, since the rear only has one sensor. Regardless of whether your diff is turning one wheel or 6, the ring gear is turning the same speed, and the tone ring is bolted to the ring gear. Now, if you had seperate wheel sensors in the rear, then a non-factory locker might cause an issue, or if you put a locker in the front diff.

You may also have an issue with slightly different tire diameters. Are all 4 tires the same size, same brand/model, and worn exactly evenly? Try measuring the rolling circumference of each tire. (A stagger tape works best. You can also wrap a sting aroung the tire, and then lay ythe string flat and measure w/ a regular tape.) If they are different, even by a little (I forget the exact tolerance), it could affect ABS, as well as put stress on the transfer case. The best way to avoid this is to always buy tires for a 4x4/AWD vehicle as a complete set of 4, and to rotate them regularly.

.....Anway, back to our regularly scheduled programming for this thread.....

 

[hms79]

I had exactly the same incident on my '98 Sport. I paid it little attention, as it is my secondary vehicle. However, after a while, the hub started making a loud grinding noise. While the hub is not the cheapest repair (anything over $50 is expensive to me) it is not overly difficult. There is a great step by step instruction right here on this section.

 

[99SportX]

I actually had this problem after replacing both of my front hubs. I occasionally have the ABS go off at low speeds when braking and then the light comes on. Most of the time now though, the light just stays on. I installed the sensors from my old hubs into the new ones and the problem still continued the same. It kinda sucks but I went an entire winter without ABS and I really don't miss it. I don't know of any way to troubleshoot my problem without a special dealer scan tool to monitor wheel speed sender signals.

If your hubs are high mileage, then you might as well change them both.

 

[Carguy3J]

I actually had this problem after replacing both of my front hubs. I occasionally have the ABS go off at low speeds when braking and then the light comes on. Most of the time now though, the light just stays on. I installed the sensors from my old hubs into the new ones and the problem still continued the same. It kinda sucks but I went an entire winter without ABS and I really don't miss it. I don't know of any way to troubleshoot my problem without a special dealer scan tool to monitor wheel speed sender signals.

If your hubs are high mileage, then you might as well change them both.

The problem is, when the ABS doesn't work, neither does your Auto 4wd. If the ecm/GEM doesn't have accurate wheel speed data, it won't know that you have wheel slip, and won't know when to engage the T/C clutch.

 

[99SportX]

Hmm, I haven't thought of that. I will try to fix it again sometime this summer. The auto 4wd seemed to work ok this winter, but it would probably work better if I fixed the ABS.

 

[inh]

Who needs Auto 4wd when you have a manual 1354

And if you dont have a manual 1354, you should get one!

 

[my pos mounty]

I actually had this problem after replacing both of my front hubs. I occasionally have the ABS go off at low speeds when braking and then the light comes on. Most of the time now though, the light just stays on. I installed the sensors from my old hubs into the new ones and the problem still continued the same. It kinda sucks but I went an entire winter without ABS and I really don't miss it. I don't know of any way to troubleshoot my problem without a special dealer scan tool to monitor wheel speed sender signals.

If your hubs are high mileage, then you might as well change them both.

Since you only mention replacing the front sensors, have you tried the rear sensor? It may be the source of your problem. Its located on your rear differential and is the only electrical connection on the housing.

 

[Duster Doug]

Sounds like I am having brake issues on just before I come to a complete stop/ low speeds (2000 XLT 4L 4x4 2ndgen). Front ABS sensor eh? Guess I'll drop into the dealer to get a diagnosis of the problem...