I have been having an issue with the ABS activating when coming to a complete stop. I removed and cleaned both ABS sensors and mounting surfaces but the problem will not go away.

I have plotted the ABS sensors with a scan tool while driving and all three sensors show the exact same data - but the ABS still activates.

Any suggestions?

-Greg

Sounds as if a wheel bearing has to much clearance. Or your sensor(s) is still to far from the reluctor ring.

The time to snapshot the sensors is always under 10 mph. One will have broken resolution or fail to output correctly right around 8mph on the decel. They will always read correcty at higher speeds, or else the ABS light would be illuminated.

Sounds as if a wheel bearing has to much clearance. Or your sensor(s) is still to far from the reluctor ring.

The time to snapshot the sensors is always under 10 mph. One will have broken resolution or fail to output correctly right aound 8mph on the decel. They will always read correcty at higher speeds, or else the ABS light would be illuminated.

I did the snapshot on the sensor under 10mph and everything matches perfect for three stops despite the fact that the ABS does kick on. Shouldn't it show up?

BTW - The truck has 43k miles, ABS light is not on but always activates the last 5 feet when coming to a complete stop. When reading the computer with the scan tool there were old codes which showed a problem with all three speed sensors but we cleared them and they didn't come back.

If the wheel bearing was bad or the sensor was to far from the ring, would that show up on the snapshot? The wheel feels tight when shaken.

-Greg

I have a 01' and at about 50K miles that was happening to me. I drove around with that for about a week. While i did this the ABS light did not illuminate. So i pulled the the 60 Amp fuse under the hood and it stopped activating on me at low speeds on decelleration. Seeing how it is a three-channel system, I believe that it is the front sensors being too far from the reluctor wheel. I'm not in too much of a rush to fix this because, the front hubs are still tight. But, there is a groaning noise coming from the hubs that just appeared at 84K, But their is still no play in them. So, I might just replace the hubs and go from there

I believe that it is the front sensors being too far from the reluctor wheel.

How do you fix this?

-Greg

I did the snapshot on the sensor under 10mph and everything matches perfect for three stops despite the fact that the ABS does kick on. Shouldn't it show up?

If the wheel bearing was bad or the sensor was to far from the ring, would that show up on the snapshot? The wheel feels tight when shaken.

-Greg


The best way to snapshot the sensors is by traveling at 2mph steady and reading the three inputs, then repeat at 3, 4, etc. One of the front two is certainly of lower resolution. Brake activation is not required. At some low mph, two off the three sensors will come online before the other.

Also, when you cleaned the mounting surfaces for the sensor flags up front, they need to be completely smooth. It is not uncommon to have a little raised "ring" where the allen headed bolt goes.

The best way to snapshot the sensors is by traveling at 2mph steady and reading the three inputs, then repeat at 3, 4, etc. One of the front two is certainly of lower resolution. Brake activation is not required. At some low mph, two off the three sensors will come online before the other.
Also, when you cleaned the mounting surfaces for the sensor flags up front, they need to be completely smooth. It is not uncommon to have a little raised "ring" where the allen headed bolt goes.

heymccall - thank you for your responses.

All three sensors are not giving any readings below 5mph....all of them drop to zero. Not sure if this is the scan tool or the sensors, but I would think it would be the sensors.

Could this be related to the problem?

Statistically speaking, the odds of all 3 being poor is 0%.....

isn't the three-channel the two front one's and the one in the transfer case? So if the speedometer is working then it is one of the front sensors that is the culprit. i could be wrong though...

isn't the three-channel the two front one's and the one in the transfer case? So if the speedometer is working then it is one of the front sensors that is the culprit. i could be wrong though...
The ABS needs more complete info from the third sensor than the speedo does. The speedo will be erratic only once the third sensor signal is nearly gone. Also, failure of the 3rd sensor to send complete info nearly always results in activation of the ABS lamp, while incomplete front sensor info does not generally illuminate the ABS, but will cause unintended ABS activation between 8mph and 3mph when braking.

The problem is still one of the two front sensors.

The ABS needs more complete info from the third sensor than the speedo does. The speedo will be erratic only once the third sensor signal is nearly gone. Also, failure of the 3rd sensor to send complete info nearly always results in activation of the ABS lamp, while incomplete front sensor info does not generally illuminate the ABS, but will cause unintended ABS activation between 8mph and 3mph when braking.

The problem is still one of the two front sensors.

The mechanic was using a Snap On Modis scanner which for whatever reason did not read below 5mph. You have me convinced it's a front sensor issue...so I would be willing to just buy two new sensors and go from there.

However, is it possible for the sensor to fail w/o throwing an ABS code? - I grinded all the rust from the mounting surface and I am still getting ABS activation w/no codes thrown. Should I just buy the new sensors at this point?

Thanks for all your help!

However, is it possible for the sensor to fail w/o throwing an ABS code? - I grinded all the rust from the mounting surface and I am still getting ABS activation w/no codes thrown. Should I just buy the new sensors at this point?

Thanks for all your help!


Yes, the sensor can give poor info and not turn on the ABS lamp. Therein lies the achilles heel of the system, and is the reason behind the earlier year truck recalls.

As a last ditch effort, I would elevate the front of the truck off the ground, disconnect the sensor on each side and make two measurements with a multimeter.

First, compare the sensor resistance across the two pin plug. They should be the same side to side. The bad one will have the higher (larger number) resistance in Ohms.
Secondly, measure the mv output of each sensor while hand spinning the wheel. The readings should be comparable. The bad one will generate less (lower number) AC mv than the other.

Careful inspection of the truck side plug(s) is also in order, as a few on here have had corrosion of the truck side harness, which can also give poor performance.

First, compare the sensor resistance across the two pin plug. They should be the same side to side. The bad one will have the higher (larger number) resistance in Ohms.
Secondly, measure the mv output of each sensor while hand spinning the wheel. The readings should be comparable. The bad one will generate less (lower number) AC mv than the other.

I ran outside and measured the resistance - 1016 (ohms?) on the passenger side and 1032 (ohms?) on the drivers side. Don't even know what I am measuring - just happen to have the meter :-). I will try spinning the tire tomorrow am and post as it's dark already but looks like the drivers side could be the culprit.


Careful inspection of the truck side plug(s) is also in order, as a few on here have had corrosion of the truck side harness, which can also give poor performance.

Are you referring to the harness that the sensor plugs into?

Great info - I really appreciate your help

-Greg

1016 vs 1032 is to be considered identical, and as such, the windings in both sensors, along with their pigtail harness, are to be considered good.

Placing the meter into AC mv and spinning the wheel will give the actual output of each sensor and will allow comparison of the output signal strengths. This will tell if one sensor is "too far" from the reluctor ring (the toothed wheel within the hub assy). Whichever one takes more spin to generate a repeatable signal will be the one suspected of being too far out.

You have the Variable Reluctance type. http://www.carquest.com/common/downloads/partsTechBrakeCQB%2001-01.pdf

1016 vs 1032 is to be considered identical, and as such, the windings in both sensors, along with their pigtail harness, are to be considered good.

Placing the meter into AC mv and spinning the wheel will give the actual output of each sensor and will allow comparison of the output signal strengths. This will tell if one sensor is "too far" from the reluctor ring (the toothed wheel within the hub assy). Whichever one takes more spin to generate a repeatable signal will be the one suspected of being too far out.

You have the Variable Reluctance type. http://www.carquest.com/common/downloads/partsTechBrakeCQB%2001-01.pdf


I think the problem has been solved! This morning I tried to get an AC mv reading, however I found it very difficult to "generate a repeatable signal" - seemed the mv output was fluctuating back and forth as I could not maintain a constant speed.

So I decided to take the wheels off again and check the sensor mounting surface....and everything looked pretty good. During re-assembly I noticed that the sensor was not sitting flat. I had pushed the sensor in by hand and then put the allen bolt in, however the o-ring must have provided some resistance and therefore although the allen bolt was tight, there was a slight gap between the sensor and the surface. So I tapped it down lightly with a hammer and then it sit flush with the surface.

My main concern when I took it apart the first time was to clean the surface. I guess the best practice for performing this repair would be to tap the sensor in and then put the allen bolt it as it does not sit 100% flush otherwise. This is a very sensative system!!!

I did about 5 stops on my road - no ABS activation. So far so good

Thank you so much for your help!

-Greg

how much are new sensors?

how much are new sensors?
New sensors are only required if they break during removal (for corrosion cleanup), of if the wires have rubbed through somewhere.

http://www.dieselplace.com/forum/showpost.php?p=3582256&postcount=5

do i need to take the wheel bearings off to clean the sensors? someone was saying i need to clean a gear type thing inside the bearings too?

do i need to take the wheel bearings off to clean the sensors? someone was saying i need to clean a gear type thing inside the bearings too?

Remove the wheel (22m)
Slightly collapse the caliper assy (with a C-clamp)
Remove the slide bolts (18mm) and lift aside caliper (do not hang by it's hose)
Remove the caliper ear (21mm 6PT socket) (later reinstalll to 221 lb/ft torque)
Slide off the rotor, and you'll see the sensor and it's allen bolt.

Just the sensor needs pulled and most WILL break when trying to remove them.

http://www.dieselplace.com/forum/showthread.php?t=333033

http://www.mightyautoparts.com/pdf/articles/gb0804.pdf

New sensor P/n http://www.dieselplace.com/forum/showpost.php?p=3582256&postcount=5

alright ill take it off and try and clean it up, the sensor was brand new friday with the wheel bearings so i dont think it is dirty....

alright ill take it off and try and clean it up, the sensor was brand new friday with the wheel bearings so i dont think it is dirty....

It may not be seated correctly, or it was damaged in shipping.

the shop i bought the wheel bearings from (timken bearings) is going to give me a set of new sensors for free to try out and send the others in as defective. hopefully this solves my problem