Disco 2 Odd Traction Control Behaviour

Hello folks.

I'm looking for some guidance to help narrow down a problem with my 2001 TD5 Disco traction control. Only had it a week and I've no real experience of Disco TC. But, had plenty of other trucks and cars with TC. I'm no mechanic, but I think this is within my limits.

Scenario 1: Good grip, such as tarmac or hard compacted ground. On full right hand lock moving forward slowly, such as parking, the TC light comes on and I hear the buzz of (I assume) the ABS unit doing it's thing. However, there's no discernable "braking" going on. IMO the TC shouldn't activate at all given the surface and available traction.

Scenario 2: Driving along a normal metaled road, say 30 MPH, the nearside hits a drain grate that has dropped, say 1", or a small pot hole. You get a noticable thunk as the suspension absorbs the sudden dip, which you'd expect I think. But, the TC light come on, the ABS unit buzzes and, again, no discernable "braking" going on. If I had to say, I would be inclined to say it happens when the front wheel hits the pot hole.

I read some other posts and I'm guessing that there is likely to be an issue with the nearside front ABS sensor, which is where I plan to look first. But, the lack of any "braking" when the TC light comes on and the ABS unit buzzing concerns me as the other posts indicate that this usually results in the truck being braked.

Given the above, am I right to look at the near-side front ABS sensor first or should I be looking else where first?

I have a workshop manual with the details of how to remove the callipers & disc to get to the sensor. But, before I go down this route (which will be more spannering than I have done in about 20 years), I thought it best to consult with the community.

Thank you in advance.

Yes TC behaviour is VERY sensitive to sensor inputs, the best for you would be to plug in a tester for live data inputs otherwise you can chase the problemat the wrong place... btw is your car on standard dimension tyres? at least i hope all 4 are the same and the pressures are close to the recommended ones... first step would be to make sure that there are even pressures in axle pairs

Mine does the same over bumps on the odd occasion. It hasn't really bothered me enough to do much about it yet, however it doesn't do it when cornering. I'm reluctant to start messing with the sensors, as I don't want the 3 amigos to pop up!

sierrafery said:

Yes TC behaviour is VERY sensitive to sensor inputs, the best for you would be to plug in a tester for live data inputs otherwise you can chase the problemat the wrong place... btw is your car on standard dimension tyres? at least i hope all 4 are the same and the pressures are close to the recommended ones... first step would be to make sure that there are even pressures in axle pairs

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Hi Sierrafery, thanks for the advice.

Yes, it has standard alloys and 255/55/18 tyres - ones an Avon (front nearside) and the others are Wranglers. Good point about tyre pressures. I did notice that the drivers front was low when I got it home in daylight one evening last week and it was down at 14psi, so I promptly inflated that and matched both fronts. I will check whether it's started to deflate again as that may be the contributor!

I am sooooo glad I asked first.

Haystacks said:

Mine does the same over bumps on the odd occasion. It hasn't really bothered me enough to do much about it yet, however it doesn't do it when cornering. I'm reluctant to start messing with the sensors, as I don't want the 3 amigos to pop up!

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Thanks Haystacks. I've seen the 3 amigos mentioned, now I've just learnt what they are. This would be bad.

It does sound like this is a "feature" of Discovery ownership.

TheWoodsmane said:

Hi Sierrafery, thanks for the advice.

Yes, it has standard alloys and 255/55/18 tyres - ones an Avon (front nearside) and the others are Wranglers. Good point about tyre pressures. I did notice that the drivers front was low when I got it home in daylight one evening last week and it was down at 14psi, so I promptly inflated that and matched both fronts. I will check whether it's started to deflate again as that may be the contributor!

I am sooooo glad I asked first.

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Hi, the other first thing to do would be to put 4 exactly similar tyres cos even different types of same dimension can affect ABS system behaviour, also if a hub was changed at a point and it was not at least OEM with wabco sensor can mix up the system especially if it was cheap stuff.

sierrafery said:

Hi, the other first thing to do would be to put 4 exactly similar tyres cos even different types of same dimension can affect ABS system behaviour, also if a hub was changed at a point and it was not at least OEM with wabco sensor can mix up the system especially if it was cheap stuff.

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Spooky.

I have literally just come in through the door having checked the tyre pressures and the offside front is down again about 6psi, so I've got a leak (a bit of a theme with the truck). Whilst I was down there I had a peak at the sensor cables and the near side is new. I did have the nearside hub assembly replaced yesterday (I thought it was off-side) with an OEM unit (by Challenger 4x4) as there was more play in the bearing than a long weekend of Shakespeare in the Park - the new sensor says Wabco on it and they tell me they only use OEM spec. That said, this TC feature has been happening since before the hub assembly was replaced. So, this kind of rules out the sensor as a pro fitted a new one with the hub.

Next step I think is get the tyre repaired and swap them for the rears which are the same and see if there's any change.

Once again Sierrafery, many thanks for the advice.

welcome, it's good that this hub is OEM but if one of the others is not you have the same problem though your problem might be due to pressure difference too so let's hot that's it

Sierraferry. I didn't mention this in the battery post but this noise of something trying to engage and nothing happening was also common for me. Always present when I dropped the girls to preschool. It happened at the same spot which was where the Tarmac turned to pavement. I am talking like every single day. Again since taking the battery out and leaving it to fully charge, this sound and the three amigos have gone.
Would it be possible for ther people with this problem to charge their batteries over night to full and then review the results.

sierrafery said:

welcome, it's good that this hub is OEM but if one of the others is not you have the same problem though your problem might be due to pressure difference too so let's hot that's it

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Well, the tyre is repaired, the pressures are now equal 28 & 38 front & rear and the same type of tyre with almost identical wear are on the front axle...so now just wait and see if it happends. If I still get it, the spare is the same type of tyre, but with about 3mm more tread. I'll swap that for the odd one on the rear axle.

Sadly, equally tyre pressures haven't solved it. I'll swap the spare for the odd tyre and see if that improves things.

Hi, are you aware that different brands of tyres have different highs even if they have same size printed on?

Is it road legal to use different tyres on one axle in your country? here in Austria it is a MOT failure.

Here is MOT failure even if you don't have standard dimension tyres like in the official documents... which IMO is good for safety as i made several tests and i know how bad bigger tyres can affect/increase the ABS deceleration threshold and braking distance, all the ABS system's capabilities are reduced with approx the same percentage like the difference between standard and bigger tyre dimensions...without considering different tyres on axles or axle pairs which is the worst scenario

I have always kept the same tyres on the same axle, in fact I prefer to have the same tyres on all axles. In this case, I only picked up the truck a week ago Monday and as of this morning, I'll at least be back to 4 of the same, with an odd spare. I'm not comfortable with tyres of differing performance characteristics on the truck, but hadn't connected that to the TC issue - seems obvious now that it's been explained

I have 255 55 19 on my D2, front axle are Pirelli, rears are good years,
Both have 6mm tread, but I don't have any ABS issues, so if it was me I'd be looking at a hub/bearing fault before swooping for matching tyres, at least get it on a tester

In this case is not a ABS fault cos the system passed the self check and rolling diagnostic checks, a fault that would have triggered the 3 amigos, it's TC erratic behaviour due to signal missbalance and that CAN be caused by different tyres too from one case to another

Right, spare is now on.

That was quite an experience, damn those alloys are heavy! Thought I would struggle to find a use for that torque wrench I bought years ago when I was spannering my Fireblade! But, no, wheelnuts now at 140NM. I also acquired a 12v wheel nut gun - not sure it was necessary, but as I'm nursing a cracked rib, it made short work of the "wrenching" too.

To my surprise, the jack and chocks were all intact and worked as well. Bonus.

Now, I have four identical tyres (other than the rear offside has a few more mm of tread than the rest). It's off to road test and then check the wheel nuts again, followed by a jet wash I think - for the truck AND me! Fingers crossed that this cures the TC issue.

johnlad said:

I have 255 55 19 on my D2, front axle are Pirelli, rears are good years,
Both have 6mm tread, but I don't have any ABS issues, so if it was me I'd be looking at a hub/bearing fault before swooping for matching tyres, at least get it on a tester

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Sadly, no tester - if anyone knows of one near Guildford that permits use for drinking vouchers, I'd appreciate intro. I'd be interested to see how my MAF is doing - I don't think the truck is up to full puff,but I have nothing to compare it to.

The spare makes a set of four, so no expense, just some grunting. I guess the hubs may be the next check after this if the wheel swap doesn't work.

sierrafery said:

Here is MOT failure even if you don't have standard dimension tyres like in the official documents... which IMO is good for safety as i made several tests and i know how bad bigger tyres can affect/increase the ABS deceleration threshold and braking distance, all the ABS system's capabilities are reduced with approx the same percentage like the difference between standard and bigger tyre dimensions...without considering different tyres on axles or axle pairs which is the worst scenario

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Hey sierrafery, this is interesting as I am considering a lift and increased wheel / tyre size in my future to improve off-road performance (and because IMHO it looks awesome). But, could you expand on the impact here on ABS etc? Seems I need to weigh up this downside.

Road test was a mixture of success and failure. It actually drove much better, unless that's just a perception and not reality, with all four tyres being the same AND the TC did not activate any where near as much. It cut in twice, once on almost full right lock leaving my drive (which is gravel, so I guess it could be genuine, though I was doing about 2mph) and once at almost the end of a 20 minute drive where I wouldn't have expected it to cut in, considering all the pot holes, sunken man-hole covers and drain grates I aimed at.

Regardless, this is progress with a capital P (thanks Sierrafery for advice here) as it is much improved. So, I guess the next step is to look at the hubs / sensors that haven't been changed yet and see. I will check the free play in the wires and that then maybe remove, clean and refit the sensors. Opinions encouraged .