P38 ABS - Help me please!!!!!

Hi , I call on the heads of wisdom, before I pull out all my hair.............
Can anyone help with the follow problem I have - Please

P38A 2002 (MY99+)
·Wabco Type D ABS.
·ABS fault / TC failure were intermittent on turning on ignition and would clear once driven.
·ABS fault / TC failure now permanent on turning on ignition.
·The BECM is storing a “rough road signal not hardware fault” (P1590)?
·Both Testbook and Hawkeye say “Rear Left sensor short between sensors”
·When you unplug any other sensor it says “XX sensor short between sensors” XX being sensor removed –the same fault code?!?
·Recently had a new accumulator.
·New ABS and ABS pump relays.
·ABS pumps works and kicks in after 5/6 pedal pushes.
·Brake fluid sits on Max as it should.
·It has had a new battery to rule out any voltage issues and charges ok.
·All four ABS sensors replaced.
·Ohms and voltage check of sensors and sensor loom/harness to ABS ECU all show as ok.
·New ABS ECU (SRD100501) plugged in – on ignition showed the same fault code!!!!
·Old ABS ECU back on car and ticking for self-diagnostics and still showing same fault
·Speedo works all ok.
·Brake Switch changed - Hawkeye says both brake switches are engaging/brake lights work
Currently ABS fault followed by TC failure on turning ignition on. Shows only TC failure when turning off engine.
A fault with the brake servo inlet/outlet? Or BECM?
Thanks

I had something similar and it was a loose front wheel nut ....

Hi SpiggyTopes, do you mean one of the 5 wheel bolts??

No.

The nut holding the hub was loose allowing the whole hub to move enough to upset the abs sensor.

No idea how it was caused, just mega relived when it was tightened ... and the fault disappeared.

I understand now, thank you I will check this out.
Cheers

Fluid should sit at max AFTER the pump has stopped not before it runs.

Hi Wammers, thanks. It might not be clear above, but that is what’s happening, fluid over max then pump runs and it drop to sit on max.

Owen89VSE said:

Hi Wammers, thanks. It might not be clear above, but that is what’s happening, fluid over max then pump runs and it drop to sit on max.

Click to expand...

Ok that is good. Just making the point, some wonder why they get a low fluid warning after pump has run.

Owen89VSE said:

Hi , I call on the heads of wisdom, before I pull out all my hair.............
Can anyone help with the follow problem I have - Please

P38A 2002 (MY99+)
·Wabco Type D ABS.
·ABS fault / TC failure were intermittent on turning on ignition and would clear once driven.
·ABS fault / TC failure now permanent on turning on ignition.
·The BECM is storing a “rough road signal not hardware fault” (P1590)?
·Both Testbook and Hawkeye say “Rear Left sensor short between sensors”
·When you unplug any other sensor it says “XX sensor short between sensors” XX being sensor removed –the same fault code?!?
·Recently had a new accumulator.
·New ABS and ABS pump relays.
·ABS pumps works and kicks in after 5/6 pedal pushes.
·Brake fluid sits on Max as it should.
·It has had a new battery to rule out any voltage issues and charges ok.
·All four ABS sensors replaced.
·Ohms and voltage check of sensors and sensor loom/harness to ABS ECU all show as ok.
·New ABS ECU (SRD100501) plugged in – on ignition showed the same fault code!!!!
·Old ABS ECU back on car and ticking for self-diagnostics and still showing same fault
·Speedo works all ok.
·Brake Switch changed - Hawkeye says both brake switches are engaging/brake lights work
Currently ABS fault followed by TC failure on turning ignition on. Shows only TC failure when turning off engine.
A fault with the brake servo inlet/outlet? Or BECM?
Thanks

Click to expand...

BECM does not store any fault codes.
Is this a message on the dash?

Hi Datatek, The fault is on the BECM to clear, isnt it the BECM that puts the ABS light on the dash?
Yes TC failure is coming up on the message centre. ABS & TC failure on ignition (Not with engine started) and TC failure when swithing engine off.
Rgds

the tc message when you start and when you turn the engine off is normal if an abs fault is present. mine did it until i changed the faulty abs sensor then it cleared its self.

silly question but are your abs sensors seated correctly ?
where did you buy them? the ebay cheapo one i fitted lasted a month.

Owen89VSE said:

Hi Datatek, The fault is on the BECM to clear, isnt it the BECM that puts the ABS light on the dash?
Yes TC failure is coming up on the message centre. ABS & TC failure on ignition (Not with engine started) and TC failure when swithing engine off.
Rgds

Click to expand...

May be the way your diagnostics system presents it, the BECM does not store faults, the fault will be stored in the ABS ECU.
As others have said, may be a sensor, however often it's the ABS ECU has failed. Was the replacement you tried a new one of an Ebay special?

The sensors all seated until stopped, not the most expensive, but they show good resistance on the multi meter from the ECU plug. The ECU was a brand new one. I just plugged it straight in. Some say it may have needed initialising?? However an ECU repair guy said that ECU wasn’t that clever??
I suspect the hub or servo.

Owen89VSE said:

The sensors all seated until stopped, not the most expensive, but they show good resistance on the multi meter from the ECU plug. The ECU was a brand new one. I just plugged it straight in. Some say it may have needed initialising?? However an ECU repair guy said that ECU wasn’t that clever??
I suspect the hub or servo.

Click to expand...

Never done one, but I believe the ABS ECU is Plug & Play.
Sensor resistance may not be a good guide to function.

That’s my understanding too. Fair point - I was going to check the wheel speed of the sensors on Hawkeye (live data) when i check the hub nuts. I will start with the faulting rear left and see what it says.
If a sensor is shot, does the speed take the average from the remaining three sensors to keep it working?

Owen89VSE said:

That’s my understanding too. Fair point - I was going to check the wheel speed of the sensors on Hawkeye (live data) when i check the hub nuts. I will start with the faulting rear left and see what it says.
If a sensor is shot, does the speed take the average from the remaining three sensors to keep it working?

Click to expand...

I cannot remember, but quite likely.
If you have one faulting, that is certainly the place to start.

I had Classics for years, until the rust got hold. I never thought a P38 could be such a problem (but always had it in the back of my mind). Even with my own diagnostics........which hasn’t really diagnosed anything meaningful, albeit Testbook has said exactly the same thing.
Frankly, I’m close to giving up on it – too many electrics to go pop!

Owen89VSE said:

That’s my understanding too. Fair point - I was going to check the wheel speed of the sensors on Hawkeye (live data) when i check the hub nuts. I will start with the faulting rear left and see what it says.
If a sensor is shot, does the speed take the average from the remaining three sensors to keep it working?

Click to expand...

Speedo works off sensors at 8000 pulses per mile. It only take one sensor to be doing that to make the speedo work i would think. Don't think averages of all the sensor readings comes into it. One sensor giving a different reading will only effect ABS and TC.

Have you tried swapping the rear sensors from side to side to see if the fault follows?

Most ABS sensors should read 1000 Ohm +/- 100 Ohm. So first step is to check the resistance of the windings.(knowing Land Rover, theirs might be different so start with a known good one).
If that is OK, check the resistance of each of the connectors to earth (the body of the sensor) - there shouldn't be any connection there, so if you get any resistance reading the sensor is scrap.

Also, how did you check the loom? Did you do a voltage drop test under load? or just a resistance test?

Hi, Both rear sensors new.
Unplugging a sensor trips the same fault
I unplugged each sensor and tested resistance - rear 1140 both and front 0900 - i understand 0900 to 2000 ohms is ok. I then checked each wire to earth on each loom wire from the ecu. I then used an old sensor to create a 1.6v tester with a battery and plugged in at the sensor end and read the v on the ecu socket = 1.6v on each sensor loop. I know now the loom is A1.
I suspect the exciter ring/sensor interface. It was however very clean in there.