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1995-2002 Range Rover P38A
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27 Posts
Discussion Starter #1
Hi All,

My P38 failed the MOT on split dust boots on both front lower suspension ball joints and leaking rear oil seal.

I have had to remove the front brake calipers, discs and hubs complete with drive shafts to be able to change the lower ball joint dust boot.
I did have to use a clamp to press the brake pistons back when refitting, i did unscrew the brake fluid cap but some people have said doing this can cause damage to the master cylinder not sure that this would cause the issue i have though

I also removed the same on rear to replace oil seal.

After refitting everything i had the traction control light and ABS lights come on as soon as ignition is switched on even before starting the engine.

Believing that it was probably an ABS sensor i scanned with Nanocom to find no error codes under ABS. I then scanned everything and the only code i had was P1592 Rough Road Signal Implausible.

Checking the inputs via Nanocom i have found that the voltage for Rough Road is constantly switching between 0 Volts and 12 Volts, i am not sure if this is meant to happen i suspect not.

I have gone back round and checked the ABS sensors Via Nanocom and the Voltage of each sensor is 3.31 Volts and the wheel speeds are reading 1.7 KPH on each sensor even though the vehicle is not moving.

Using a D.V.O.M i have a resistance of 960 Ohms per sensor and an AC Voltage of between 0.4 and 0.8 Volts while rotating the wheels.

No error codes are being found under ABS using the Nanocom and when trying to drive to check voltage i loose communication quickly, i think this is normal and believe the ABS ECU stops communication above a certain speed that is actually very slow maybe 8 KPH.

Unplugging all sensors gives a short to another sensor code for each one so it feels like the ABS system and sensors are maybe not at fault and that this is something to do with the Rough Road issue.

All air suspension is working with no codes and Nanocom reports ride height values within 1 of requested value across all heights and sensors.

I have run an ABS test with Nanocom and pump looks to be running OK.

Any thoughts would be great especially on the voltage switching every second or so.

In case it helps its a 2000 (X Reg) Thor engine
 

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FOUNDING MEMBER
1995-2002 Range Rover P38A
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491 Posts
The ABS and TC lamps are supposed to illuminate when the ignition is switched on before the engine is started. The TC lamp should extinguish after a short delay and the ABS lamp will extinguish after the vehicle reaches ~5mph.

Do both lamps stay illuminated and do you get an audible bleep and a fault message in the display?

in removing the front hubs have you possibly damaged or dislodged a reluctor ring on one of them?
 

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1995-2002 Range Rover P38A
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27 Posts
Discussion Starter #3
Today i have double checked all four sensors and they all read about the same 950 to 960 Ohms resistance and a AC output of between 0.4 and 1.2 if i spin them fast enough. I used my Hantek Oscilloscope to check the AC wave pattern and it was clean and consistent. I would imagine a damaged or dislodged reluctor ring would have shown on the AC wave form

Yes TC light comes on and stays on before engine starts along with the audible bleep and message on dash.

After plugging in all the sensors and giving each one a light tap to make sure they are seated properly i was no further forward so decided to just park her up and look online for some information.

To my surprise as i drove down the road to turn around the warning lights turned off and everything was working as normal. I started to reverse to park in my garage when the TC and ABS lights both popped back on again, a quick scan and the P1592 Rough Road Signal Implausible came back.

Wondering if it was something to do with reversing i cleared the codes with engine off ignition on (the TC and ABS light stayed on) drove down the road and again the lights all turned off, another quick scan and the P1592 code had now gone. Pulling forward ready to reverse back into the garage and hey presto they pop back on, quick scan and P1592 code is back again.

The P1592 is the intermittent code that appears to be turning the TC and ABS lights on, every time i manage to clear the Rough Road Signal code and drive off the TC and ABS error goes.

The trouble is without an MOT i cant really drive far and see if it keeps coming on and off and i am sure that at the re-test for the rubber boots the tester would see the lights and fail the vehicle on the new issues.

Any information on the setting criteria for this P1592 or how the Rough Road Signal is sent to the BCM or ABS module or wherever it comes from and goes might allow some testing to see what is going on. I have seen a post saying that the brake light switch not working can cause the ABS and TC errors but my brake lights are working and no codes are being detected by the Nanocom about brakes anyway, and as with every scan the ABS never shows any error codes other than when i unplugged them.
 

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The trouble is without an MOT i cant really drive far and see if it keeps coming on and off and i am sure that at the re-test for the rubber boots the tester would see the lights and fail the vehicle on the new issues.
As said, the TC light will stay on until the ABS pump has got the system up to pressure and the ABS light will stay on until you reach 5mph. If the lights only come back on when you reverse, you can drive it to the MoT station for the retest and unless you have to reverse it, then it should pass. If your testing station is anything like the ones I use, you'll drive it in and reverse it out so they won;t realise until after they have checked your work and issued the certificate.
 

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1995-2002 Range Rover P38A
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27 Posts
Discussion Starter #5
Ok so i decided to clear the code and risk putting in for MOT re-test.

Drove off from home after leaving her parked up all night, TC and ABS lights both cleared once i started to drive. Had to park at the garage and this involved reversing, no light came on so happy i waited for the result.

Tester came in happy with repairs and informed me that as he reversed of the ramp the warning lights came on, he said it was probably due to him levering the vehicle to check play in ball joint was fixed. He said that it would turn off when i drove off down the road so issued the certificate.

Drove off from garage to local shop, parked up got shopping the reversed out of parking space and drove into petrol station. A car moved off a pump so i reversed again to change into empty pump and switched off engine to refuel, no warning lights still.

Drove off after fuelling and approx 1 mile down the road light came back! Got home switched off ignition and back on then drove a few meters down the road and again lights turned back off.

Whatever this is is now intermittent and with the new MOT i will not be playing any more as i only use the vehicle once a week to go a mile or two to just keep her being used.

Every time lights come on the Rough Road Signal code is the only thing that comes up. I did read on another post that one owner was told that this can happen after lots of jacking up and down but would clear itself over a few days! not sure that is true but whatever sensor is causing the issue i think must only just be out of spec every now and then.

Its a real shame that this rough road system does not have more information on exactly how it works what modules and sensors cause it. Glad i don't have to worry any more but feel really sorry for anyone who has this issue in the future and that this is not my long distance driver.
 

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1995-2002 Range Rover P38A
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1,422 Posts
Glad you got the MOT.
It seems possible that you have a minor wiring issue. Have a close look at where all of the wires from the sensors meet the chassis and look for chafing. Second, more likely possibility that comes to mind is the standard loose / corroded earth point and a current loop causing a false signal.
If you think about it, when you chuck one of these into reverse, there are like 6 systems that activate from reversing lights to dipping mirrors. A bit of a bad earth in any of these could be the issue. Think about combinations of current sources.....Like: you put it in reverse, and ABS pump runs since you pressed the brake......Also got the brake light system now.......It would not hurt to run the electrical tests in sticky at the top of the forum.....Check all earths you can find. Rave has a good list.
I HATE tracing intermittent faults! :think:
 
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