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This started on a dark and stormy night last Christmas......
I was driving home from California on the Coast Highway so as to avoid a large Sierra snow storm on highway 5.
the coast route had snow and ice as well, and as soon as I hit it, I got ABS and TC lights on! Not sliding or braking, so coincidence????
Pulled over, cycled ignition, and issue went away for about 10 miles, then on again.
Pulled off again, attached Nano, and looked for faults. None reported for brake system??
So, as it was 3am and I had been driving for 14 hours, I drove on.
Oddly, the ABS and TC seemed to be actually working...

For the last year, I have looked into the problem a couple of times, and again, no faults are ever reported by Nano.
When you turn on the ignition, and without starting the engine all 3 amigos go on.
After about 15 seconds, the Brake light goes off, and the message center beeps telling me I have an ABS failure.
Once I start the engine, and move the vehicle a small distance, (the usual distance that is needed to extinguish
the TC and ABS lights) the message center tells me I have Traction Control Failure.
I have 2 2002s here, and a 1999, so I compared readings from the Nano.
I get 2.33 to 2.35 volts on all sensors on all 3 and the nano says I am doing 1.7kph at a standstill.

Since this is an issue of the system failing at self test and before even starting the engine, and since all initial
readings for all 3 vehicles are virtually identical, I thought possibly it was an issue with the ABS ECU. So,
I pulled the working ECU from the 02 Borrego, and placed it in Bolt.
The issue went away for about 100 yards, then came back with the same message center warnings.
Anyone have any ideas so far??

Now, it gets stranger......I took the known good ABS ECU back out and installed it back in the Borrego.
The Borrego now has the SAME SYMPTOMS!!!!!
Identical behaviour when I switch on ignition.
Installing the ECU in Bolt for 5 minutes seems to have affected it. Again, no errors logged to be read by Nano!
Now I have 2 02s with the same issue. One that started on the road, and the other started in the shed by swapping in the ECU to Bolt.
Can anyone think just what is going on here, because I am stumped!
I hesitate to try the ECU from the 99, because it works...... but may take the Borrego ECU and try it the 99 to see if the problem shifts as expected........
Cheers,
Tom

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I think you, like me, need an exorcist!
I have a recurrent failure that is addressed as "brake switch failure" but I went through three already.
I discovered I have a "rough road" input even when the vehicle is standing, so I suspect ABS sensor(s) are the culprit.
When I have time I will pursue that option, since all data to the ABS ECU comes actually from them.

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I have had a similar issue with ABS in that nano reported wheel sensor voltages OK and speed readings were apparent from each sensor but the ABS and Traction faults were still flagged up on the dash. However, nano did tell me a wheel sensor was at fault. It turned out that the resistance of that particular sensor was higher than the other three but not spectacularly so. Changing the sensor cured the fault.

I concluded that the static POST of the system measures the resistance of each sensor (probably by current draw) and flags a fault if out of spec.

In your case the fault is may be ‘lodged’ in the ABS ECU unit and needs clearing - there is a fault there as that is what triggers the dash indications. The faults clear themselves in the WABCO D unit the system is rectified but I am unfamiliar with the workings of earlier units.

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Update on the situation with Bolt.
I put her up on jack stands to lube the ujoints and do a general inspection in preparation for a 2000 mile RT South to see the family.
When I did the wheel bearing check, I found the RT front bearings were toasted.
Left seemed ok, but as they are stock and with 185,000 on the clock, I ordered both sides.
This made me think that possibly the RT ABS sensor had been damaged by the eccentricity in the hub.
It looked undamaged, so I checked it against a known good one and resistance was close, so I swapped it in anyway.
Same problem, however, I did catch the Nano actually telling me there was an electrical fault with the RT Front sensor
and that this had happened 6 times. This is the first time that It has actually given me a fault read out.
I also got it to stay connected long enough to get a speed reading for all 4. RT front is dead. Stays at 1.7 kph

So, 2 questions......
First, do I recall reading posts that have said the Nano is a bit dyslexic when it comes to L and R sensors? Is the problem really on the left?
Second, If the sensor is ok, what set of plugs does the ABS go through to get to the ECU. Kick panel plugs are a bit tatty, but cleaned
recently (Need to chop and solder them soon.)
I am temporarily not able to access Rave from here.
New theories?

As an aside, the front hub swap out was the easiest thing I have ever done on a front end! Great design.
Took 20 min to remove the old one, and a bit less to put it back together, and that is including the brakes and wheel.
The same job on my 85 Classic would have been all day.

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The nano is, as you say, a bit ‘dyslexic’ regarding the voltage measurements but because it just reports the fault in the Wabco ECU verbatim it is accurate with regards to which sensor has an error.

Edit: Just checked and wrt the right front the nano is actually correct with voltage measurements as well - it’s the only one though!

Edit 2: According to RAVE there are no connectors twixt the Wabco ECU and the wheel sensor flying leads.

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When I had a right rear sensor problem, the Nano reported the correct one. Although I did check the resistance to confirm it wasn't telling fibs.....

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Here's the original post from the Nanocom forums by MartyUK. Not sure if it only applies to WaboD or C as well. There's been no indication whether BBS fixed it or not.


_Had a look at a couple of P38's with ABS problems, which have both turned out to be the wheel speed sensor. The Nanocom will come up with the fault code of what sensor is faulty, so that's easy enough to troubleshoot/replace...

However, if you go into the Nanocom Inputs window in the WABCO D ABS (I can't comment on the 'C' as I've only looked at Thor vehicles lately!) I've seen that with the dodgy sensor, 3 sensors have shown a proper voltage reading and one (the faulty one) has shown 0.00V.

However the issue is that the one showing the fault isn't the same as the one the fault is logged against. So I did a run around of the vehicle plugging/unplugging each sensor in turn and found that the Nanocom labels are slightly incorrect:

When Front/Right was unplugged, it showed 0.00V on Front/Right sensor
When Front/Left was unplugged, it showed 0.00V on Rear/Right sensor
When Rear/Right was unplugged, it showed 0.00V on Rear/Left sensor
When Rear/Left was unplugged, it showed 0.00V on Front/Left sensor

Is it possible to get this looked into (I guess it just needs the labels changed, or the values moved to line up with the correct labels) for a future software update?

Just to confirm, any fault codes stored in the ABS ECU which relate to a specific sensor are correct - it is only in the inputs where it shows the sensor voltages that they don't line up. I am not sure if this carries over to the wheel speed readings aswell, as the ABS ECU won't give live data above 5mph, so haven't had a chance to test that yet._


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So,
If it reports Rt front sensor error, it is actually the Rt front?
I was able to get the nano to stay connected with live data to 30kph and 3 out of 4 sensors agreed. Rt front said 1.7 the whole time.
As for wiring and plugs.......The plug connections to the sensors are a moulded plastic with a bit of Red and White wire attached.
Do these go straight to the ABS ECU? no splices??
If so, (Gilbert) does anyone have the pin outs at the ECU for the inputs so I can ring out the wiring?
Made the 999.7 mile trip South in 16 hours with no issues and in sublime comfort, so now away from shop but still keen to get this sorted.
There are several 2001 and 2002 P-38s at breakers within 50 miles of me, so I can get another ECU or sensors if needed easily and cheaply.
I may get snow and Ice on the return and whilst not necessary, ABS and TC are nice to have......
Cheers, and Happy Thanksgiving to those who celebrate it!
Tom

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No intermediate connections, the wires from the plugs go directly to the ECU.

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Thanks Gilbert!
You are once again a hero!
Just what I need to slay this gremlin.
Cheers!

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Got under the dash and had a look.........
The sensor wires are so obvious, no diagram needed......Still, thanks again!
I feel a bit of a dolt for not taking a closer look first!
I am still baffled.
The sensors ring out at the connector as:
LF- .951k
RF- .943k
LR- .961k
RR- .919k
Wires are intact to all sensors.
Message center will still throw TRACTION FAILURE error a few seconds after switching on ignition
and without starting the engine or moving. So, it must be failing the self test.
Nano still shows no faults after driving a bit even though TC and ABS lights are on and it has thrown
the ABS FAILURE message at me after moving a few yards.
I can only get a fault that will show on Nano by unplugging a sensor, in this case the RT Front. Nano then reports RT front sensor failure.
From Pete12345's post, it seems the only wheel that does not get confused is indeed the Rt front???
I would conclude from this that it is an ECU failure, yet swapping in one from the Borrego that had no issues
showed the same error, then the error moved to the Borrego.

Other than having 2 ECUs with the same failure, I have to admit, I am currently out of ideas. Guess I will need to
swap in the ECU from the 99 when I get home. I cannot think of anything the vehicle could be doing to harm them, so caution
to the wind, I will have to try that......
Unless someone has another idea I can try?

Looks like the 16 hour drive home will feature at least 6 hours with ice and snow. ABS and TC would be nice, but, of course not mandatory....
Thanks for the assistance so far......

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950k Ohms ish? As in just under 1 MegOhm? I don't have one to hand to check and it's cold, wet and dark outside so I'm not going out to confirm, but from memory something in the region of 1.2kOhm is what I'd expect to see.

I've seen a problem with a Wabco D system where checking the wheels speeds all were showing the same speed but one was sluggish to start registering. The message, as you rightly say, will be it failing the initial self test.

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There are decimal points in front of the numbers.....
So a bit below 1.2, but all the others report correctly on Nano.
All report 1.7 kph static.
What stumps me is the lack of any faults reported by nano???
Also, fail of static self test.
Again, when I was able to get live data up to 30 kph, Rt Front showed only the 1.7 kph.
So, definitely a problem, but swapping in known good sensor did not work, and known good ECU did not work.
I have now confirmed that wiring is fine.
What am I missing?

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While testing the wiring, did you check that one of the sensor wires isn't maybe shorting to the body somewhere?
If it's chafed through its insulation somewhere and touching the body then the resistance test would be fine but I suspect the ABS controller does an inductance test too, which a short to the body would fail. Obviously as you start driving a short to the body would also pull the wheel speed signal low and that sensor will show no wheel rotation.

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I've seen that on a Wabco D too, 1.7kph when standing still whereas the earlier C will show 0.0kph. No idea why it always thinks you are moving though.

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For the Wabco D system (don’t know about other previous systems) when a sensor is replaced the power on self test will pass for ABS but the Traction warning in the DIS will remain until the vehicle is driven and then shut down and then restarted at which point it, too, will go away.

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Earlier Wabco C ones give an ABS Fault on the dash, followed by Traction Failure when moving, after which the message goes out but the ABS and TC warning lights stay on. Traction Failure then comes up for a few seconds when you turn the ignition off.

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Gilbertd wrote:

Earlier Wabco C ones give an ABS Fault on the dash, followed by Traction Failure when moving, after which the message goes out but the ABS and TC warning lights stay on. Traction Failure then comes up for a few seconds when you turn the ignition off.

That is precisely what Wabco D does as well. Message centre beeps at me on switch off to remind me I have not solved
the problem! Nag Nag Nag!

Just got in from the 2300 mile return to Southern California.
Average speed for the entire trip was 62 mph and average Mpg was 18.1 (with our smaller gallons)
Flawless performance until 50 miles from home when EAS tossed an error saying Pressure Switch was closed, permanent fault.
Cleared fault with Nano and drove on, no issues.
Fortunately, the winter storm that we were looking at was delayed by 12 hours, so with a 15 hour and 45 min 1000 mile run today, we just got a
small snow flurry and a few showers so ABS and TC were not missed.
Still need to get to the bottom of this!
I have a Faultmate II registered to Bolt, so I will pull out the old XP laptop tomorrow and have a look with that.....Who knows???
I will also check all sensors to earth to eliminate that possibility.

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That’s not how Wabco D operates, well not how mine works. If you have replaced a faulty sensor with a good one then on start up the ABS and Traction lights will extinguish as normal but the system ‘nags’ you via the DIS of the Traction Failure (which isn’t there anymore) and then proceeds to erroneously nag you for a few seconds of a non existent Traction Failure when you subsequently switch the ignition off. I assume this is because the Traction Failure is logged in the Wabco D unit and will not reset until the next power off/power on - seems a bit of an inbuilt software oddity. When you subsequently restart all the warnings are reset and normality resumes - no lights, no DIS nags. If you continuously have a Traction Failure warning then that’s something other than a repaired faulty sensor!

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"If you continuously have a Traction Failure warning then that’s something other than a repaired faulty sensor!"

Ahhhhh......Now there is the ongoing 1000 dollar (Or GBP) question.....What is the other "something"?

What you have said could explain why the error transferred to the Borrego when I moved the ECU back there.
I will do a road test and cycle the ignition to see if it clears.
The major question remains: Why are the TC and ABS lights on, faults reported on Message center, and no faults flagged on Nano??

The investigation continues.......