Disco 2 ABS common/known problem?

The story starts with a little light laneing which I concluded with a couple of trips through a ford "to get the worst off" I broke the front bumper doing so but didn't think much of it at the time.

The following day, the three amigos came on. The first time I've ever had a warning light on since 2011 and I get three at once! Well, it was christmas day......... erm, thanks disco.

So, I bought myself a diagnostic setup that I'd been considering for a while and eagerly awaited it's arrival. When it finally came, I read the codes to find "47 rear right sensor output signal too low- intermittent" but on the live data I found the front left wasn't reading 2.2v stationary but the other three were. As it happened, I changed both front hubs in November and still had the old ones about so I replaced the sensor on the n/s/f and got 2.2v on all four - job done? Sadly not, cleared fault codes and test drive put 3 amigos back on. Back to rear right.

I replaced the rear right hub and sensor today but after clearing the codes and test drive, my three christmas presents are back and the fault code is the same old "47 rear right....etc"

I haven't looked much so far but I'm hoping there's something simple - is there another plug above the fuel tank or whatever that's known for getting wet in it? Any other suggestions?

what diagnostic too do you have? some of them used to mix up fault codes when it comes to SLABS quite often, nanocom included

sierrafery said:

what diagnostic too do you have? some of them used to mix up fault codes when it comes to SLABS quite often, nanocom included

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That's not the best news ever, it's a delphi something or other. I'll have a look

What ever it is you can't trust it 100% when it comes to SLABS fault codes as long as it's not hawkeye, lynx, autologic or testbook T4 (the only ones made on the original LR diagnostic protocol)

Fair one but for now it's the best I have to work with, is there nothing that springs to mind that might say rear right sensor even when the sensor and ring SHOULD be fine?

Is there no one you know whos got a nanocom or hawkeye just incase your getting a duff code from your reader ?

The hub and sensor were new yesterday, fault still came back after being erased and then test driven

cj_uk said:

Is there no one you know whos got a nanocom or hawkeye just incase your getting a duff code from your reader ?

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Sadly not, I'll see if I can spot anything in the live data

Thin_trucker said:

Sadly not, I'll see if I can spot anything in the live data

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Hello mate,just sticking my oar in, I'm no expert on this, I know a couple of people had a similar problem and it turned out in the end that the new sensors they'd put on were faulty.Obviously you put faith in a new part but you can end up chasing round in circles for ever

Also,

Have you tried disconnecting the sensors and seeing if the fault appears for another wheel, only ask as someone once had a fault and found that a PO / Garage had at some point put the sensors on the wrong inputs. So RH rear was not RH rear.

Cheers

Thankyou both, I'll have a potter about and see what comes up

What brand were the sensors? I’d only use genuine ones. My disco had new hubs at the back before I bought it and they came with some cheap nasty abs sensors. Going by the invoice they had only lasted a month.

Actually, the front ones only lasted about three months and the replacement rear isnt genuine (though I did try to find slightly better quality). Surely it should still be enough to stop the faults at least for a few days though.

I'll get the live data on the go and see if anything shows up and then start disconnecting sensors to check that it's telling me the right corner.

If the signal is weak as it says, it should be clear to see on the graph - my gut feeling is that either the wire has chafed where it goes over the chassis by the fuel filter or there's another connection somewhere that got wet

Wasn't there an issue with using different manufactured hubs, genuine vs non-genuine, whereby the ring tooth gap differs and the signals from the different hubs cause a mismatch ? I maybe wrong .....

cj_uk said:

Wasn't there an issue with using different manufactured hubs, genuine vs non-genuine, whereby the ring tooth gap differs and the signals from the different hubs cause a mismatch ? I maybe wrong .....

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Yes there is, if you do a search you will find it mentioned a few times. You can count the teeth thru the ABS sensor hole.


Cheers

What I know so far (for what it's worth)

All 4 sensors say 1.7kmh when stationary, all 4 say 2.2v and the graphs all go up exactly the same (when driving in a straight line) and vary slightly when driving round a curve, as I'd expect, yet the fault remains the same

Just my opinion but if any of the sensors were a mismatch, wouldn't it read a different speed?

Something else that I noticed was that it doesn't come up with the fault when started with the cdl in (which puts abs and tc lights on).

3 amigos come on as I get above a certain speed, between 5 & 10 mph I think

As @neilly has eluded to, you'd be advised to check the number of segments or teeth on each reluctor ring.
The signal returned from each sensor to the SLABS ECU is an AC signal, in effect a tone, the frequency of which is directly proportional to the speed of each wheel. The value of the voltage returned from the sensors is largely immaterial in recording the speed, it does however have a bearing on whether the sensor is the correct distance from the reluctor ring.

brian47 said:

As @neilly has eluded to, you'd be advised to check the number of segments or teeth on each reluctor ring.
The signal returned from each sensor to the SLABS ECU is an AC signal, in effect a tone, the frequency of which is directly proportional to the speed of each wheel. The value of the voltage returned from the sensors is largely immaterial in recording the speed, it does however have a bearing on whether the sensor is the correct distance from the reluctor ring.

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Would a different signal not show up as a different speed to the other three then? I.e. if three sensors are seeing 100 pulses per second (100hz) and showing 15mph. If the other had finer teeth and was seeing 150 pulses, wouldn't that wheel show as doing 22mph ish in the live data and stand out like a sore thumb? Obviously it's probably not quite as exaggerated but I currently have all four wheels showing exactly the same speed when the vehicle is travelling in a straight line.

And, just to clarify, the fault (47 rear right sensor output too low - intermittent) was there before and after the new hub & sensor and clearing fault codes