P38A ABS Fault and Traction failure from ignition II

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DanClarke said:
Do you have a Nanocom?
When I fixed mine (4-Wheel ABS Wabco-D) the failed sensor was showing a 0v reading on the ECU although it had 5.3v at its supply plug.
When I changed it for a new one it showed a similar Nanocom reading (2.1v Vs 2.3v) to all the others and the fault was fixed.
When you say you have 4.8v in your post above, where was that reading measured/taken from?
Click to expand...

I don’t have a nanocom, any of the scanner readings I’m giving are from an Autel Maxidiag. The Autel can give me a pretty good idea of what’s going on with the wheel sensors - I get voltage, speed, - along with any possible simple faults like short to another sensor etc.

I’d love a Nanocom but for the price of buying it (with duty and conversion I live in Ireland) - I could get 4 new air bags and shocks to reinstate the air suspension!

All of the 4.8v are from the car side plugs, the ohms readings are the sensor side.

On the Autel I get readings around 2.3-2.4v on all the sensors - and a consistent speed reading on all 4 - also no errors showing anything like “short to another sensor” - the only error I get (which I can clear but it comes back straight away) is the ecu ground or reference ground fault.

I’ve been able to find several write ups on the abs system for the discovery II that mention the same kind of error I am getting (abs ground fault/reference ground fault) - but since this is for a separate vehicle it’s hard to compare the systems.

I did find one technical document for the discovery II - that said reference ground should be around 0.5–1v - the Autel scanner tells me that my reference ground is 5v. The reference ground wire certainly goes the ground - I have probed it and confirmed this.

Next step really will be to run a dedicated ground wire and go from there.
 
MikeFl4 said:
I don’t have a nanocom, any of the scanner readings I’m giving are from an Autel Maxidiag. The Autel can give me a pretty good idea of what’s going on with the wheel sensors - I get voltage, speed, - along with any possible simple faults like short to another sensor etc.

I’d love a Nanocom but for the price of buying it (with duty and conversion I live in Ireland) - I could get 4 new air bags and shocks to reinstate the air suspension!

All of the 4.8v are from the car side plugs, the ohms readings are the sensor side.

On the Autel I get readings around 2.3-2.4v on all the sensors - and a consistent speed reading on all 4 - also no errors showing anything like “short to another sensor” - the only error I get (which I can clear but it comes back straight away) is the ecu ground or reference ground fault.

I’ve been able to find several write ups on the abs system for the discovery II that mention the same kind of error I am getting (abs ground fault/reference ground fault) - but since this is for a separate vehicle it’s hard to compare the systems.

I did find one technical document for the discovery II - that said reference ground should be around 0.5–1v - the Autel scanner tells me that my reference ground is 5v. The reference ground wire certainly goes the ground - I have probed it and confirmed this.

Next step really will be to run a dedicated ground wire and go from there.
Click to expand...
It certainly sounds like you are on the right track with that approach. I keep a spare Wabco-D ECU module for swap-outs, do you have a spare ECU?
 
DanClarke said:
It certainly sounds like you are on the right track with that approach. I keep a spare Wabco-D ECU module for swap-outs, do you have a spare ECU?
Click to expand...

Yes I have a spare ecu, I don’t know if it is correct. I show it in one of my earlier posts on this discussion. It’s from a 2001 parts P38 I have. Comes up a bit differently on the scanner. I actually explained it pretty well and there are some pics to please reference that for info on my spare ecu
 
MikeFl4 said:
I don’t have a nanocom, any of the scanner readings I’m giving are from an Autel Maxidiag. The Autel can give me a pretty good idea of what’s going on with the wheel sensors - I get voltage, speed, - along with any possible simple faults like short to another sensor etc.

I’d love a Nanocom but for the price of buying it (with duty and conversion I live in Ireland) - I could get 4 new air bags and shocks to reinstate the air suspension!

All of the 4.8v are from the car side plugs, the ohms readings are the sensor side.

On the Autel I get readings around 2.3-2.4v on all the sensors - and a consistent speed reading on all 4 - also no errors showing anything like “short to another sensor” - the only error I get (which I can clear but it comes back straight away) is the ecu ground or reference ground fault.
Ireland is in the EU is it not? So no duty or conversion as the Nanocom comes from Cyprus.

I’ve been able to find several write ups on the abs system for the discovery II that mention the same kind of error I am getting (abs ground fault/reference ground fault) - but since this is for a separate vehicle it’s hard to compare the systems.

I did find one technical document for the discovery II - that said reference ground should be around 0.5–1v - the Autel scanner tells me that my reference ground is 5v. The reference ground wire certainly goes the ground - I have probed it and confirmed this.

Next step really will be to run a dedicated ground wire and go from there.
Click to expand...
 
Grrrrrr said:
Depends if the fault self-clears on startup.
Click to expand...
The fault never clears, whether it’s cleared by a scanner or on start (ignition II, no engine) the abs fault and traction failure come up straight away.

I guess this means it has to be 100% electrical since the car isn’t even running/moving and the fault is present
 
OK - we have some change!

So I ran a dedicated ground from the reference ground on the ABS ECU:
IMG_6037.jpg


Not the most graceful solution but it seems to have been just enough to make a difference.

I turn the key - dash faults still appearing (abs fault, traction failure) - I cleared the error codes on the scanner and only one came back (BUT this time it wasnt that damn "reference ground fault"!)

I got the error below - Brake switch failure
IMG_6036.jpg


I removed the brake switch from my parts P38, pulled out the plunger, let the brake pedal back down to set the position etc - and it made no difference - still have this brake switch failure.
I haven't been able to check if the brake lights were working (they always worked fine in the past) - but I dont think the brake switch itself is faulty.

On the scanner I can see the brake switch position - There seems to be two so I'm not sure where the second one is?
With foot off the pedal I get this :
IMG_6034.jpg


With foot on I get this :
IMG_6035.jpg


So it appears that the brake switch (switches?) are working fine...

Ill do some more research now myself - Refreshing googling for faults that are not related to the grounding error! - Please feel free to give me some suggestions in the meantime.

The current situation regarding the faults on the dash is still the exact same - engine off - switch to ignition II - Abs fault and Traction failure come up with the abs and tc light always on. - I can clear the brake switch fault - but it seems to be a constant fault as cycling the ignition after clearing all faults still results in the dash faults coming back straight away.

I think I will run a jumper wire to the ABS ECU ground as well (I didn't bother initially as the reference ground made such a difference codes wise) - currently I only have a dedicated ground wire ran to the Reference ground.
 
MikeFl4 said:
OK - we have some change!

So I ran a dedicated ground from the reference ground on the ABS ECU:
View attachment 266391

Not the most graceful solution but it seems to have been just enough to make a difference.

I turn the key - dash faults still appearing (abs fault, traction failure) - I cleared the error codes on the scanner and only one came back (BUT this time it wasnt that damn "reference ground fault"!)

I got the error below - Brake switch failure
View attachment 266392

I removed the brake switch from my parts P38, pulled out the plunger, let the brake pedal back down to set the position etc - and it made no difference - still have this brake switch failure.
I haven't been able to check if the brake lights were working (they always worked fine in the past) - but I dont think the brake switch itself is faulty.

On the scanner I can see the brake switch position - There seems to be two so I'm not sure where the second one is?
With foot off the pedal I get this :
View attachment 266394

With foot on I get this :
View attachment 266395

So it appears that the brake switch (switches?) are working fine...

Ill do some more research now myself - Refreshing googling for faults that are not related to the grounding error! - Please feel free to give me some suggestions in the meantime.

The current situation regarding the faults on the dash is still the exact same - engine off - switch to ignition II - Abs fault and Traction failure come up with the abs and tc light always on. - I can clear the brake switch fault - but it seems to be a constant fault as cycling the ignition after clearing all faults still results in the dash faults coming back straight away.

I think I will run a jumper wire to the ABS ECU ground as well (I didn't bother initially as the reference ground made such a difference codes wise) - currently I only have a dedicated ground wire ran to the Reference ground.
Click to expand...

The brake switch has 2 switches inside.
 
Grrrrrr said:
The brake switch has 2 switches inside.
Click to expand...

Thanks, I thought I was going a bit insane there for a minute as I kept reading about these "2 brake switches" - although I could never find one!

I think that maybe the switches are supposed to invert? So like when the pedal is pressed - one is open and one is closed etc? Not sure yet as I am only just reading up on this. It seems that mine both open and close together with the pressing of the pedal.
 
I've got some nanocom guides somewhere, I'll have a read and see what it says. Have you tried going for a run, I don't think for one minute that you are not aware that the abs light won't go out until over circa 5 mph, do you know that?
 
To add, my abs problems, cured with a new sensor, made me curse initially because the light didn't go out until I hit around 20mph immediately after the sensor change but is now back to the normal circa 5mph after that hiccup.
 
MikeFl4 said:
Thanks, I thought I was going a bit insane there for a minute as I kept reading about these "2 brake switches" - although I could never find one!

I think that maybe the switches are supposed to invert? So like when the pedal is pressed - one is open and one is closed etc? Not sure yet as I am only just reading up on this. It seems that mine both open and close together with the pressing of the pedal.
Click to expand...
That is correct, they are a flip-flop pair. :)
 
Flossie said:
I've got some nanocom guides somewhere, I'll have a read and see what it says. Have you tried going for a run, I don't think for one minute that you are not aware that the abs light won't go out until over circa 5 mph, do you know that?
Click to expand...

Lol - I wish the damn light would go out over 5mph! Yes I know about this - I have never actually experienced a working ABS system in a P38 but I would think that - a working system - wouldn't say ABS Fault / Traction Failure every single startup? - My dash lights being stuck on are only a side effect of the faults...

Anyways, earlier I did take it for a drive around the yard (just slow speeds) to see if any other faults came up - and I think I have found more.

Its super weird in order to get the faults to show but the live data shows the issue consistently.

FYI - I now have both C504 pin 12 (Ecu ground) and C506 pin 3 (Reference earth) - jumped together and connected to a dedicated ground - I would think that it doesn't make a difference if they are connected together as like - a ground connection is just a ground connection right?

So, I cleared the codes and left the vehicle for a few mins to research - once I came back, turned on the key (abs fault errors etc like normal)
I read the codes on the scanner and got the following:
IMG_6047.jpg


I then read the live data, and sure enough - RR and RL inlet value values are different to the rest:
IMG_6048.jpg


The Pump Relay thing - I have no idea - this fault has kind of been intermittent the whole time - back when I had the Ground Faults - if I took the car for a good spin and read the codes after, there would be several "reference ground etc" faults and this Pump relay fault. I have removed and tested this relay - and it works fine. I've also swapped the relay with one from the other car - has no different effect. There could still be some weird problem with the ABS pump itself - I have 2 spare ones so (im kind of dreading having to change the pump AGAIN)... I might swap the pumps around again.

I then cleared the codes - cycled the ignition (still got abs fault etc) - and read the codes again - this time I only got the brake switch failure:
IMG_6049.jpg


I had a look at the live data and it was still the same as above - RR and RL inlet value values different to the rest.

So even though there is an issue in the valves it doesn't throw an error straight away. As far as I can figure out at this moment - my brake switch is working fine - tested the brake lights as well and sure enough they work perfect.

I decided to take a look at the connectors on the ABS reservoir - rusty and dirty as hell around them but inside they look fine so nothing really to report there: - no difference after plugging these in and out.
IMG_6050.jpg


Now - as I was typing this you guys made a few new comments so I will address them here also - would just like to thank you all for the help - I probably would end up reinstating the previous owners work around if there wasn't such a good community for these land rovers (previous owner connected the dashboard abs light to the seatbelt light so that the car would pass its NCT (MOT) here in Ireland...All they look for in the test is if the light turns on and off indicating system initialised but no errors)

So @Flossie - Thank you for sending on the nanocom guides. As far as bulbs on the dash go - I should have them all installed because all the damn things turn on and dont turn off! (Just the ones related to the ABS and TC circuits stay on)

@DanClarke - I felt that was the case too - that it was more of a flip flop - possibly the live data I was reading was correct but we cannot verify what "Engaged" really means. I did find in the engine ecu live data the following though.

There is this Primary brake and Secondary brake reading - maybe its unrelated but the values flip flopped when the pedal was pressed:
IMG_6045.jpg

IMG_6044.jpg


From here I can really only see two things that have either happened - that I can then do next.

1. Maybe the grounds I ran have shorted something and this is why we are getting the weird valve related open circuits? I guess I can verify this by removing my temporary ground and seeing if the valves values return to normal.

2. Since the ABS ECU is now properly grounded, im discovering several other wiring related issues - this would explain why the brake switch is constantly an error even though it appears to be correct? Also could be pointing towards more bad grounds/wiring/connectors if there are open circuits on the ABS valve system.
 
Last edited:
You sound way smarter than me:p.
When you press the brake pedal down does the readings change?
I've got nanocom and a fully working abs tc system(for now:)) .
If you like I can compare readings on mine to yours and see if there are any obvious differences?
Can do that tomorrow if you put up a list of what you want comparing?
 
Flossie said:
You sound way smarter than me:p.
When you press the brake pedal down does the readings change?
I've got nanocom and a fully working abs tc system(for now:)) .
If you like I can compare readings on mine to yours and see if there are any obvious differences?
Can do that tomorrow if you put up a list of what you want comparing?
Click to expand...

Hah, Im no smarter than the amalgamation of 15 years worth of Range Rover P38 forum posts - Im not kidding when I say that is how I've learned pretty much everything about these things!

Unfortunately nobody else in the past has had the exact same issue as me so here we are now! Hopefully we can find a solution so another poor soul in the future will be able to find this forum and fix their car too.

As far as the brake pedal readings go - On the ABS ecu live data - the Brake Switch 1 & 2 are both open when pedal is up - closed with pedal is down. I only get the flip flop effect on the readings from the engine ECM - whatever Primary Brake and Secondary Brake are - they flip flop when the pedal is pressed.

Thanks for the offer on the Nanocom readings, maybe it would be worth a shot comparing some of the values? Im actually pretty happy with the Autel scanner as so far its been very truthful and led me in the right direction.
If I do a bit more reading around in the live data (and find more wrong stuff) Ill take you up on the offer!

For now im going to disconnect my temporary dedicated ground and see if the old grounding issues come back - and that the abs valve values return to normal (aka is my ecu fried or not)
 
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