Unusual ABS fault (1 Viewer)

[billysan]

Hi all,

TLDR version: ABS activates at slow speed (10mph) with very gentle brake pressure on smooth tarmac road. Why?

Full version:
I recently refurbished the front axle on my dads UK spec 1994 J80 (using the complete roughtrax kit, inner seals, new bearings etc). I carefully removed the ABS sensors from each birfield joint and placed to one side. Having now reassembled there is an off ABS fault that was not there before. The symptoms are:
ABS warning light illuminated for 3s at ignition on, then goes out. No further faults indicated.
When gently bringing the car to a stop, and I mean gently, the ABS will activate for what feels like the front right wheel for about 0.5s. I say 'feels' as there is pedal feedback, and the car pulls slightly left when it happens, which makes me think the right hand caliper is backed off by the ABS. It happens briefly at about 10-12mph, using very gentle brake pressure only. It also happens about every third gentle deceleration.
When it happens, it is not on loose ground, the wheel is 100% not locking. All tires are matching and of equal wear. The ABS seems to be triggering falsely for no reason.
If you try to get the ABS to work properly, ie find loose ground and hit the brakes hard, it works perfectly.
The only stored code is 31, indicating front right sensor, however I cant believe this is at fault as there is no permanent light, and it works fine when you want it to.
When I had the axle in bits to do the seals, I cleaned up the stub axle and toothed ring, and the sensor. All rings were sound, no cracks evident.
In trying to work this problem out I removed the sensor and inspected the ring with a torch. The valleys between the teeth had filled up with CV grease on both sides. This excess grease was carefully removed front both with a stiff brush through the sensor hole. Retesting the car after this, this cleaning up of the toothed ring has made an improvement, in that the false ABS activation is now for less time, but it still happens.

I have not yet tried swapping L and R sensors over to see if the fault moves, I ran out of time.

Has anyone any ideas?

Thanks in advance for any assistance.

 

[ajax1]

Have you pulled the sensor back out and looked at it? Is the plug fully seated?

 

[smritte]

What ABS does is monitor wheel speed and when the stop light switch is pressed, looks at those speeds. If their all the same, nothing happens. If it sees a speed difference, it "assumes" the slower one is starting to lock up. Now the ABS locks out the offending brake until it sees the same speed from all. ABS systems need to see 3-5 mph difference to activate.

The way I interpreted your post is you replaced the axles.

With that said, loose tone ring will give an impression of too fast (spins on axle). This will make the others seem too slow. If you removed the tone rings, are they seated all the way and some are directional. This means if its backwards it wont seat properly. If they came with them, are they installed properly. Look through the sensor hole and make sure the ring is centered and the ring is tight.

Erratic signal from a sensor. This could be a wire/connector issue, sensor issue or computer issue. This could make the computer think its either fast or slow. Check everything. Swapping the sensors is an easy way to do this.

Hopefully you have enough to figure it out. Considering you worked on the front, the issue should be there.

 

[MickeyB]

Hi all,

TLDR version: ABS activates at slow speed (10mph) with very gentle brake pressure on smooth tarmac road. Why?

Full version:
I recently refurbished the front axle on my dads UK spec 1994 J80 (using the complete roughtrax kit, inner seals, new bearings etc). I carefully removed the ABS sensors from each birfield joint and placed to one side. Having now reassembled there is an off ABS fault that was not there before. The symptoms are:
ABS warning light illuminated for 3s at ignition on, then goes out. No further faults indicated.
When gently bringing the car to a stop, and I mean gently, the ABS will activate for what feels like the front right wheel for about 0.5s. I say 'feels' as there is pedal feedback, and the car pulls slightly left when it happens, which makes me think the right hand caliper is backed off by the ABS. It happens briefly at about 10-12mph, using very gentle brake pressure only. It also happens about every third gentle deceleration.
When it happens, it is not on loose ground, the wheel is 100% not locking. All tires are matching and of equal wear. The ABS seems to be triggering falsely for no reason.
If you try to get the ABS to work properly, ie find loose ground and hit the brakes hard, it works perfectly.
The only stored code is 31, indicating front right sensor, however I cant believe this is at fault as there is no permanent light, and it works fine when you want it to.
When I had the axle in bits to do the seals, I cleaned up the stub axle and toothed ring, and the sensor. All rings were sound, no cracks evident.
In trying to work this problem out I removed the sensor and inspected the ring with a torch. The valleys between the teeth had filled up with CV grease on both sides. This excess grease was carefully removed front both with a stiff brush through the sensor hole. Retesting the car after this, this cleaning up of the toothed ring has made an improvement, in that the false ABS activation is now for less time, but it still happens.

I have not yet tried swapping L and R sensors over to see if the fault moves, I ran out of time.

Has anyone any ideas?

Thanks in advance for any assistance.

You will have to get an FSM and check for faults. You can use a multimeter to check if the abs sensor at the wheel is good and the wires that connect into the driver side connector by the frame. I would do this before tearing into the axle. Luckily a special tool is not required on the 80s to center the knuckle. As long as your birf has the tone ring on right and abs sensor is pushed in and working correctly then it’s the wiring. Mine was throwing the same code and ended up having to buy the full wire kit that goes along the radius arm with new sensors because my wiring had a short. My sensors were good, but had to buy the whole kit to fix it.

 

[billysan]

Thanks for the replies.

@smritte: I didn't replace the axles, I only renewed all seals and all bearings (and rotors) on the front axles (typical axle oil leaking from felt seals on birf). The axle shafts obviously came out for me to clean up and re-grease the CVs. The stub axles were therefore removed, but the tone ring was not separated from the stub axle. It was cleaned as a single unit, and not dropped or damaged whilst doing so.

Given the ABS was working fine beforehand, and I didn't disturb the tone rings, Im working on the assumption that they are still fully seated, and are not backwards!

I do agree with your thoughts that the ABS ECU is seeing one wheel (Front RH) doing a 'different' speed.

I did do a minor bit of work to the rear at the same time, cleaned up the drum brake components, and cleaned the rear ABS sensors and Tone rings (they had probably 15 years dust and iron filings stuck on). I didn't disconnect any rear ABS component however. My gut feel is that it is not the rear, as when the ABS cuts in it feels like it is a front wheel being 'unlocked'. The final bit of work I did was to replace the front brake calipers, which seemed a good opportunity to fully bleed all brakes. I cant see this causing this issue, it feels 'electrical'.

I think next port of call is to check all electrical connections and cables, as suggested. And move the sensors around to try to isolate fault.

@MickeyB: I sincerely hope it is not the wiring, as I barely disturbed it other than pulling the sensor connector clear of the birf to avoid damaging it. Are they that sensitive to bending? It is 28 years old saying that. . . .

 

[cruiserdan]

Did you remove the sensors from the knuckles before pulling out the axle shafts? If they were in place when the shafts were pulled they may have been inadvertently damaged.

 

[MickeyB]

Thanks for the replies.

@smritte: I didn't replace the axles, I only renewed all seals and all bearings (and rotors) on the front axles (typical axle oil leaking from felt seals on birf). The axle shafts obviously came out for me to clean up and re-grease the CVs. The stub axles were therefore removed, but the tone ring was not separated from the stub axle. It was cleaned as a single unit, and not dropped or damaged whilst doing so.

Given the ABS was working fine beforehand, and I didn't disturb the tone rings, Im working on the assumption that they are still fully seated, and are not backwards!

I do agree with your thoughts that the ABS ECU is seeing one wheel (Front RH) doing a 'different' speed.

I did do a minor bit of work to the rear at the same time, cleaned up the drum brake components, and cleaned the rear ABS sensors and Tone rings (they had probably 15 years dust and iron filings stuck on). I didn't disconnect any rear ABS component however. My gut feel is that it is not the rear, as when the ABS cuts in it feels like it is a front wheel being 'unlocked'. The final bit of work I did was to replace the front brake calipers, which seemed a good opportunity to fully bleed all brakes. I cant see this causing this issue, it feels 'electrical'.

I think next port of call is to check all electrical connections and cables, as suggested. And move the sensors around to try to isolate fault.

@MickeyB: I sincerely hope it is not the wiring, as I barely disturbed it other than pulling the sensor connector clear of the birf to avoid damaging it. Are they that sensitive to bending? It is 28 years old saying that. . . .

I don’t think there that sensitive, it’s just age and wear and tear. Also had a nice layer of grease and oil on everything because it runs along the from axle. My wiring looked fine and after removed I inspected for breaks or anything that would be of concern, but resistance didn’t check out on multi meter that’s the only way I knew.

 

[smritte]

Actually they can be that sensitive. ABS is one of the classes I teach and I set up bugs like this for my students. On these analog systems, the farther away the sensor is from the tone ring the weaker the signal. The rear ones are the worse because of the wire resistance. Especially at lower speeds the signal can be too weak to properly signal the computer causing a false ABS activation. I always have people check tone rings because no one knows to check them. The most common failure here is a sensor with the second being a wire/connector issue.

 

[billysan]

Did you remove the sensors from the knuckles before pulling out the axle shafts? If they were in place when the shafts were pulled they may have been inadvertently damaged.

Yes they were both carefully removed and cleaned before removing the birfs.

Ive not looked at this since last post as my dad has been in hospital. The ABS activation was irritating him so we have just pulled the fuse for now. Hopefully will be able to look at it again in a week or two.

 

[BILT4ME]

Yes they were both carefully removed and cleaned before removing the birfs.

Ive not looked at this since last post as my dad has been in hospital. The ABS activation was irritating him so we have just pulled the fuse for now. Hopefully will be able to look at it again in a week or two.

I hope your Dad improves quickly and does well.

It could also be loose wheel bearings. If they are too loose, they may activate as the rotors and wheelbearings and hubs move around and lose proper range with the reluctor rings.

 

[COYS]

I'd give it a proper, fresh brake fluid job and test again.

And more importantly, wishing your father a speedy return to full fitness.

 

[billysan]

I hope your Dad improves quickly and does well.

It could also be loose wheel bearings. If they are too loose, they may activate as the rotors and wheelbearings and hubs move around and lose proper range with the reluctor rings.

This is a good point regarding wheel bearings as I did replace all the front ones. I will double check. The brakes were all fully bled at the time so I dont think it is that however.

 

[billysan]

Hi all. A long overdue update on this post. (I personally hate finding threads in forums that have no closure, you've no idea how the issue was progressed or resolved!)

Firstly, my dad is thankfully home again and has largely made a full recovery, for which I am very grateful.

I checked all the components in the area I disturbed, nothing untoward I could see. Bearings (wheel and pinion), brakes, bushes, etc are all fine. So I swapped the ABS sensor from one side to the other, and the fault moved also! Exactly the same symptom, but the mirror of it, ie an unnerving ABS activation with very gentle brake pressure, and only when you are just pulling up to a stop (ie under 10mph).

In my mind this is a fault sensor therefore. I didnt bother checking the continuity of the wiring, I couldn't see the point as the fault moved with that single component. Im having a tough time locating one, does anyone still supply or stock them?

Thinking about the cause of the failure, while Im not a professional mechanic I am confident and experienced with working on a range of cars, especially 90's Japanese things. I know to be careful with ABS sensors therefore, they were not mishandled at all when rebuilding the axle. So Im still at a bit of a loss as to what caused the failure.

When doing the axle, we broadly followed the process in these videos;


including the types, volumes, and process for applying grease into the CV joint and knuckle. Could excess grease cause it to fail? I cant obviously see how. Looking in through the sensor hole, the troughs between the teeth of the tone ring were completely filled with grease. The sensor had a good amount on it also. I cleaned both up, using a paint brush to clean the tone ring through said hole. This made no difference to the fault, I was able to reproduce it within 20m of driving once reassembled.

The 80 was used on tracks and lanes most days, it was no pavement queen. Im just at a loss therefore how the sensors could last 28 years of vibration in use but be fragile enough to fail upon careful removal. Just bad luck I guess.

For now we've just pulled the fuse and bulb.

 

[gummycarbs]

Looking in through the sensor hole, the troughs between the teeth of the tone ring were completely filled with grease.

I can't imagine that would matter unless it had a tremendous amount of ferrous metal shavings mixed in with it.

ABS sensor availability came up recently and everyone was saying you had to buy the entire harness and both sensors and one unit. MegaZip shows front sensors available for 1999 - 2006 models, presumably Venezuelan production. Part number 89542-60030. I have no idea if it's compatible with earlier systems.

 

[BILT4ME]

Hi all. A long overdue update on this post. (I personally hate finding threads in forums that have no closure, you've no idea how the issue was progressed or resolved!)

Firstly, my dad is thankfully home again and has largely made a full recovery, for which I am very grateful.

I checked all the components in the area I disturbed, nothing untoward I could see. Bearings (wheel and pinion), brakes, bushes, etc are all fine. So I swapped the ABS sensor from one side to the other, and the fault moved also! Exactly the same symptom, but the mirror of it, ie an unnerving ABS activation with very gentle brake pressure, and only when you are just pulling up to a stop (ie under 10mph).

In my mind this is a fault sensor therefore. I didnt bother checking the continuity of the wiring, I couldn't see the point as the fault moved with that single component. Im having a tough time locating one, does anyone still supply or stock them?

Thinking about the cause of the failure, while Im not a professional mechanic I am confident and experienced with working on a range of cars, especially 90's Japanese things. I know to be careful with ABS sensors therefore, they were not mishandled at all when rebuilding the axle. So Im still at a bit of a loss as to what caused the failure.

When doing the axle, we broadly followed the process in these videos;


including the types, volumes, and process for applying grease into the CV joint and knuckle. Could excess grease cause it to fail? I cant obviously see how. Looking in through the sensor hole, the troughs between the teeth of the tone ring were completely filled with grease. The sensor had a good amount on it also. I cleaned both up, using a paint brush to clean the tone ring through said hole. This made no difference to the fault, I was able to reproduce it within 20m of driving once reassembled.

The 80 was used on tracks and lanes most days, it was no pavement queen. Im just at a loss therefore how the sensors could last 28 years of vibration in use but be fragile enough to fail upon careful removal. Just bad luck I guess.

For now we've just pulled the fuse and bulb.

It's very possible you cracked a wire by removing the harness. I recommend you clean the harness thoroughly to locate the crack, damage, or broken wire.

Unfortunately I think this harness is NLA. Check with @slow95z and @arcteryx to see if they have a good used one.

 

[High Lander]

Firstly, my dad is thankfully home again and has largely made a full recovery, for which I am very grateful...

Very glad to hear you're dad is feeling better

Im having a tough time locating one, does anyone still supply or stock them?

Roughtrax do the whole front loom including 2 sensors for £520

I bought one 2nd hand from https://www.80breaker.com that worked fine

 

[billysan]

Very glad to hear you're dad is feeling better


Roughtrax do the whole front loom including 2 sensors for £520

I bought one 2nd hand from https://www.80breaker.com that worked fine

Thanks for the pointer. The one RT sell is for the later ODB2 80s, they no longer stock the ones for the earlier 80s like my fathers, nor are they interchangeable as I understand it.

 

[High Lander]

PM me, I have an Indian guy who is really professional and can be trusted to supply what you want

 

[billysan]

Final update to say we fixed the fault. We managed to get a used sensor from a Japanese auction. Swapped it straight in and fault no longer there! (following a test drive to check). It is worth highlighting that the ABS lamp never lit with this fault, the ABS itself just triggered on the side with the faulty sensor, but only at walking pace. Disconcerting in that just as you pulled up to a stop sign or red light it would suddenly lurch off to one side. It pulls straight to a stop now with no spurious activation.

Thanks for everones input.

 

[fjbj40]

Final update to say we fixed the fault. We managed to get a used sensor from a Japanese auction. Swapped it straight in and fault no longer there! (following a test drive to check). It is worth highlighting that the ABS lamp never lit with this fault, the ABS itself just triggered on the side with the faulty sensor, but only at walking pace. Disconcerting in that just as you pulled up to a stop sign or red light it would suddenly lurch off to one side. It pulls straight to a stop now with no spurious activation.

Thanks for everones input.

I just went through exact same thing but I know I mishandled my sensor.

Pulled like yours when braking gently. Got a spare sensor from a friend and put it in, fixed problem immediately