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I cannot remember for sure what readings I had from my brake pedal but I thought they swapped as the pedal went down. Must be on here somewhere.
P38A ABS Fault and Traction failure from ignition II
- Thread starter MikeFl4
- Start date
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I cannot remember for sure what readings I had from my brake pedal but I thought they swapped as the pedal went down. Must be on here somewhere.
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- Buckinghamshire, UK. ('95 DT)
If it logs a fault moving and doesn't clear on startup then it will just sit there reporting a fault until diagnostic software clears it.
tomcat59alan
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- wirral and triquivijate
Isn't that for the SRS ?
tomcat59alan
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- wirral and triquivijate
On the diesel yes,one controls the brake light and the other the cruise control. Don't know if the petrol brake switch is the same.
Flossie
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Of course! Yes. As I'm slowly learning about these complicated machines by reading lots of posts ..100% info goes into my shrinking brain , 95% of it is not stored, 3% is stored accurately and the other 2% is stored inaccurately and that 2% is what I post on 'ere
.
Datatek
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If the car is moving or stationary, it makes no difference fault or no fault if the sensor is good
Ok guys, so here is an update.
When I added the dedicated ground to the ABS ECU, it finally cleared my "Abs ground or reference ground fault".
This then resulted in the following faults : Brake switch failure / RR Inlet valve open circuit / RL Inlet valve open circuit
Attempts to solve the Brake switch failure:
I took the brake switch from my parts car and installed it (pulled out the plunger and had the pedal set position) - resulted in no difference. Diagnostic readings show me that the brake switch is in fact working correctly - I found the following in the electrical troubleshooting manual that I believe shows the operation of my brake switch is correct:
As far as the brake pedal readings go - On the ABS ecu live data - the Brake Switch 1 & 2 are both disengaged when pedal is up - engaged with pedal is down. This doesnt really look right as its suppose to flip flop. Since we dont really know what "engaged" means - this isnt really 100%. If we look at the ECM Live data - whatever Primary Brake and Secondary Brake are - they flip flop when the pedal is pressed. This lines up with what the electrical diagrams says so I assume the fault is not with the brake switch itself.
Attempts to solve the RR & RL Inlet valve open circuit:
So this is kind of a new one for me as I really don't know anything about the actual ABS valve system bits in these cars.
From what I could research, these valves are contained within the Brake Modulator (that big thing with all the pipes coming out of it below the reservoir)
I did the obvious first, disconnected and cleaned all associated connectors, probed the main brake modulator plug for solid ground on the ground wire (perfect), grounds were already cleaned but I cleaned and tightened them again just to be sure. - All resulted in no change
Then, from my previous experience with the ABS ECU grounds, even though the probing checked out - the dedicated ground wire was still necessary. So I tapped into the brake modulator connector and ran a direct ground. This also had no change...
I then took off a portion of the insolation on the firewall to inspect the wiring harness visually, it all looked perfect.
Breaking the problem down into its simple elements - and basing it on what the diagnostics is telling us - It seems that simply the RR & RL Inlet valve are not getting any ground connection. On diagnostic live data we can see every other valve sitting around 0.07v (which is correct for a stationary vehicle) where as both the RR & RL Inlet valve are over 3v. In my opinion, based on my previous grounding fault with the ABS ECU, this can only mean that its a ground issue as - before I ran a dedicated ground for the ABS ECU, the reference ground was over 4v, now with dedicated ground, it sits at around 0.01v (the correct reading)
Looking at the electrical diagram below, It seems that the ABS Booster unit (modulator) only has one dedicated ground (circled below) which I have already checked / bypassed.
Otherwise, the only other place the modulator could be getting ground is from the ABS ECU - which I have already properly grounded.
Just incase there was a really specific fault with this ABS ECU - I swapped it for my spare and got the exact same results - Brake switch failure / RR Inlet valve open circuit / RL Inlet valve open circuit
So I believe this is one of two things:
1. Maybe I have not dug deep enough into the wiring and there is something else corroded/broken etc that I am missing (only way really to know would be to probe all of the associated wires with the valves in question.
2. I have an internal problem with my ABS modulator - I have read a bunch of stuff about early model P38s having some issues with the modulators but this only seems to be a physical washer degradation type of thing. The only electrical problems I could find were to do with Discovery II, but that system seems to not really be comparable as it uses a different setup.
My next move (which is going to take me awhile as so far I haven't been able to find any details on how to remove it) is to swap the ABS Modulator from my 2001 parts car (I would only remove it from the parts car - keep my existing modulator in the P38 in question here - and just connect the connectors to see if we have the exact same electrical valve faults - That would pretty much entirely rule out whether this is an internal fault with the modulator or wiring related.
If you guys have any input on all this stuff I have put up here, suggestions are highly appreciated, although I feel we are out of he realm of an easy "tap in the sensor/plug it in and out again" style fix.
OTHERWISE - If there is anyone in Ireland selling a V8 P38 WITHOUT any faults - I'm just about ready to give up on this one and buy one that's not so broken!
Conspiracy Theories: On the diagram above for the Modulator - See the part that says "C0362" - the "C" indicates that this is a connector. The problem occurs when you look for said connector in the connectors section on the electrical manual - it simply does not exist! It just jumps from "C0359" to "C0369L"
The only reference to this elusive "connector" I could find was on a Discovery II - it turns out that Land Rover figured the Discovery was too good for the simple categorisation of "E" meaning "Earth" or "C" meaning "Connector" - as on the Discovery - "C0362" is an earth cable for the ABS system! So basically, I cant say that for certain I probed the right thing as C0362 literally does not exist - but anything that looked like a ground that was around the modulator checked out as correct.
When I added the dedicated ground to the ABS ECU, it finally cleared my "Abs ground or reference ground fault".
This then resulted in the following faults : Brake switch failure / RR Inlet valve open circuit / RL Inlet valve open circuit
Attempts to solve the Brake switch failure:
I took the brake switch from my parts car and installed it (pulled out the plunger and had the pedal set position) - resulted in no difference. Diagnostic readings show me that the brake switch is in fact working correctly - I found the following in the electrical troubleshooting manual that I believe shows the operation of my brake switch is correct:
As far as the brake pedal readings go - On the ABS ecu live data - the Brake Switch 1 & 2 are both disengaged when pedal is up - engaged with pedal is down. This doesnt really look right as its suppose to flip flop. Since we dont really know what "engaged" means - this isnt really 100%. If we look at the ECM Live data - whatever Primary Brake and Secondary Brake are - they flip flop when the pedal is pressed. This lines up with what the electrical diagrams says so I assume the fault is not with the brake switch itself.
Attempts to solve the RR & RL Inlet valve open circuit:
So this is kind of a new one for me as I really don't know anything about the actual ABS valve system bits in these cars.
From what I could research, these valves are contained within the Brake Modulator (that big thing with all the pipes coming out of it below the reservoir)
I did the obvious first, disconnected and cleaned all associated connectors, probed the main brake modulator plug for solid ground on the ground wire (perfect), grounds were already cleaned but I cleaned and tightened them again just to be sure. - All resulted in no change
Then, from my previous experience with the ABS ECU grounds, even though the probing checked out - the dedicated ground wire was still necessary. So I tapped into the brake modulator connector and ran a direct ground. This also had no change...
I then took off a portion of the insolation on the firewall to inspect the wiring harness visually, it all looked perfect.
Breaking the problem down into its simple elements - and basing it on what the diagnostics is telling us - It seems that simply the RR & RL Inlet valve are not getting any ground connection. On diagnostic live data we can see every other valve sitting around 0.07v (which is correct for a stationary vehicle) where as both the RR & RL Inlet valve are over 3v. In my opinion, based on my previous grounding fault with the ABS ECU, this can only mean that its a ground issue as - before I ran a dedicated ground for the ABS ECU, the reference ground was over 4v, now with dedicated ground, it sits at around 0.01v (the correct reading)
Looking at the electrical diagram below, It seems that the ABS Booster unit (modulator) only has one dedicated ground (circled below) which I have already checked / bypassed.
Otherwise, the only other place the modulator could be getting ground is from the ABS ECU - which I have already properly grounded.
Just incase there was a really specific fault with this ABS ECU - I swapped it for my spare and got the exact same results - Brake switch failure / RR Inlet valve open circuit / RL Inlet valve open circuit
So I believe this is one of two things:
1. Maybe I have not dug deep enough into the wiring and there is something else corroded/broken etc that I am missing (only way really to know would be to probe all of the associated wires with the valves in question.
2. I have an internal problem with my ABS modulator - I have read a bunch of stuff about early model P38s having some issues with the modulators but this only seems to be a physical washer degradation type of thing. The only electrical problems I could find were to do with Discovery II, but that system seems to not really be comparable as it uses a different setup.
My next move (which is going to take me awhile as so far I haven't been able to find any details on how to remove it) is to swap the ABS Modulator from my 2001 parts car (I would only remove it from the parts car - keep my existing modulator in the P38 in question here - and just connect the connectors to see if we have the exact same electrical valve faults - That would pretty much entirely rule out whether this is an internal fault with the modulator or wiring related.
If you guys have any input on all this stuff I have put up here, suggestions are highly appreciated, although I feel we are out of he realm of an easy "tap in the sensor/plug it in and out again" style fix.
OTHERWISE - If there is anyone in Ireland selling a V8 P38 WITHOUT any faults - I'm just about ready to give up on this one and buy one that's not so broken!
Conspiracy Theories: On the diagram above for the Modulator - See the part that says "C0362" - the "C" indicates that this is a connector. The problem occurs when you look for said connector in the connectors section on the electrical manual - it simply does not exist! It just jumps from "C0359" to "C0369L"
The only reference to this elusive "connector" I could find was on a Discovery II - it turns out that Land Rover figured the Discovery was too good for the simple categorisation of "E" meaning "Earth" or "C" meaning "Connector" - as on the Discovery - "C0362" is an earth cable for the ABS system! So basically, I cant say that for certain I probed the right thing as C0362 literally does not exist - but anything that looked like a ground that was around the modulator checked out as correct.
Last edited:
- Posts
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- Buckinghamshire, UK. ('95 DT)
All P38s have issues it is their age.
Spare modulator sounds good. I did take one apart once but I cannot recall that clearly what was inside but there's not a lot that looks fixable.
The ABS pressure switches have been known to fail. Not sure how that ties into the wiring or how it might affect the earth if it did fail but might be worth checking the diagram.
It’s a shame there isn’t more documentation on the modulator, loads for the Disco II but pretty much nothing for the P38 (I can’t even find a proper guide on how to remove it!). Good to know that the modulator itself is not some super complex box of magic, should be easy enough to discern whether it’s broken or fine.
I believe that the issues must be linked (brake switch and the valve stuff) as when before I fixed the ABS ECU grounds - I never ever had a brake switch or valve issue. Possibly they were broken the whole time but being hidden by the duff ground issue?
I’m hoping that once I figure out the valve issue - the brake switch will sort itself and the system will finally start working correctly! I don’t see a situation where more things break as I’ve touched every single component of the system at this stage, the damn thing has to give up eventually even if it means completely rewiring the ABS system!
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- Buckinghamshire, UK. ('95 DT)
Its removal is in RAVE. Tight access but easy enough. Only bind after swapping is getting all the air out. I used litres of brake fluid although that modulator was dry.
I might have some pictures on an old PC somewhere but from memory the base plate came off and underneath you can see the connections for the solenoids. There's one for each wheel. Then there's a chamber all the way through from the brake pedal and that has the springs and washers on it. That was about it.
Datatek
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If it's not the actual ECU, based on what you have done so far I would have to bet on it being a wiring/connector issue which is not much help.
Ah perfect, I dont know how I missed that, I agree it actually looks fairly straight forward. I probably wont be disassembling the modulator itself, just swapping them around for diagnostic purposes.
Ofcourse I cant be 100% sure that its not the ABS ECU, but I mean, since both the ecus give the exact same error when swapped around... It must not be ecu related. Theres a good chance it could still be wiring, it seems probing is useless as it just gives me the false illusion that everything is fine, so running new wires will be the way to go if the other modulator doesnt give any change.
There won't be any duty or currency conversion. Blackbox Solutions are based in Cyprus which like Ireland is in the EU so you pay in Euros & only have to pay VAT.
https://blackbox-solutions.com
Ah, I didn't actually notice, I just assumed it was based in the UK since all they did was Land Rovers. Ill hold onto my money for the time being and try some more swapping around as im actually fairly happy with the Autels diagnostics for the ABS system. If I ever attack the more P38 specific items (blend motors, EAS etc) Ill certainly get one. Thanks.
UPDATE.
It has been almost a year…
I am updating this for future reference in case any other poor soul happens to have a similar problem, only to find this post and see that there is no conclusion! Note: my problem is not fixed yet, I just have hit a major milestone allowing me to actually progress.
I bought a Nanocom, unfortunately not much help at the beginning as it told me only really what my old scanner did - the biggest difference is that the Nanocom was able to control stuff. I always found it was odd that I had 3v readings on two of the eight valves for the ABS modulator - now using a Nanocom I was able to activate all of the valves, only the realise that the ones which were at 3v would not fire.
I tested the pin outs from connectors C0506 to C0501 (abs ecu to modulator) and all the pins were perfect with no shorts - must not be a wiring issue.
I then just decided, the “easiest” next step was to remove the ABS modulator from my parts car. Honestly, not the worst job I’ve had to do on a P38 but certainly very awkward as almost every bolt or nut it about 1cm from the firewall.
Eventually, I got it out this evening…
*pic to follow, for some reason it says I dont have permission?*
Brought it in to my “good” P38 and just plugged it in while leaving everything else in place, looks pretty funny actually.
*pic to follow...*
Turn the ignition on - and... What?? no instant Abs Fault? No Traction Failure message??
I was quite stunned that by literally just plugging in a different modulator, the errors were gone straight away. So, it appears that I dont have a wiring issue, or a grounding issue - I have some kind of internal failure inside the modulator itself which is causing all of my issues.
I would like to add some more pics of this but I dont have permission to post them for some reason.. anyways - Here we are! Some kind of actual development in this whole story.
Its certainly not fixed yet, I had been able to get it to produce the fault messages but this is a big step in the right direction as I now have something to work with.
It has been almost a year…
I am updating this for future reference in case any other poor soul happens to have a similar problem, only to find this post and see that there is no conclusion! Note: my problem is not fixed yet, I just have hit a major milestone allowing me to actually progress.
I bought a Nanocom, unfortunately not much help at the beginning as it told me only really what my old scanner did - the biggest difference is that the Nanocom was able to control stuff. I always found it was odd that I had 3v readings on two of the eight valves for the ABS modulator - now using a Nanocom I was able to activate all of the valves, only the realise that the ones which were at 3v would not fire.
I tested the pin outs from connectors C0506 to C0501 (abs ecu to modulator) and all the pins were perfect with no shorts - must not be a wiring issue.
I then just decided, the “easiest” next step was to remove the ABS modulator from my parts car. Honestly, not the worst job I’ve had to do on a P38 but certainly very awkward as almost every bolt or nut it about 1cm from the firewall.
Eventually, I got it out this evening…
*pic to follow, for some reason it says I dont have permission?*
Brought it in to my “good” P38 and just plugged it in while leaving everything else in place, looks pretty funny actually.
*pic to follow...*
Turn the ignition on - and... What?? no instant Abs Fault? No Traction Failure message??
I was quite stunned that by literally just plugging in a different modulator, the errors were gone straight away. So, it appears that I dont have a wiring issue, or a grounding issue - I have some kind of internal failure inside the modulator itself which is causing all of my issues.
I would like to add some more pics of this but I dont have permission to post them for some reason.. anyways - Here we are! Some kind of actual development in this whole story.
Its certainly not fixed yet, I had been able to get it to produce the fault messages but this is a big step in the right direction as I now have something to work with.
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I find copy and paste pictures into the message works for me
Well done on the progress you've made
Datatek
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Good work that man, thanks for the update
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+1 on data post thanks for updating
- Posts
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- Buckinghamshire, UK. ('95 DT)
As far as I recall the bottom plate comes off. I cannot recall what is in there. There might be a circuit board but all I remember is the 4 solenoids that activate each brake circuit. It wasn't complex.
