P38A ABS Fault and Traction failure from ignition II

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MikeFl4

MikeFl4

Active Member
Posts
104
Location
Ireland
Hello everyone,

Just looking for some help on this issue please, since I have bought this vehicle its had a persistent ABS Fault and Traction failure message along with the two standard ABS and TC lights. They appear straight away once the I turn to ignition II and the ABS and TC light stay on the whole time.

I originally had a short on the front right sensor - bought a new one and this is now all happy.

I unfortunately don't have anything P38 specific like a Nanocom but I do have an Autel scanner - using this it can tell me:

All 4 sensors seem to be happy - they all show 2.3-2.4V and all output a speed signal (obviously only up to like 5kph since the ABS ECU stops communicating once you go faster - but they all read perfectly fine)

The main error code it gives me is : "ECU ground or Reference ground fault"

Intermittently I get : "Pump relay driver fault"

Also to mention - live data on the ABS ECU, there is a reading called "Reference ground" and this reads as 5V.

Things I've done:
New abs accumulator (this was weak anyway so needed to be replaced)
Cleaned all the related ground points E056X etc ones
Cleaned the connectors in the LH foot well - one of the wires was corroded to the point where its metal tab broke so I cut and soldered them together - others looked fine once cleaned but maybe I should just chop and solder all of them?
Swapped around ABS ECUs (I have a parts P38, I don't know if the ECU is any better in the parts car but its handy to have a second anyway - it still gives the exact same "reference ground" error)
Swapped around the ABS relay (from parts car), no difference.

Something I've noticed:
Even after installing the new abs accumulator - it still seems to take over 20 seconds to charge up - also possibly runs a little too often between pedal presses - I actually have two spare abs pumps (used, random condition) so maybe its worth just swapping one of these in?

Additional information:
The air suspension was removed from my P38 (I eventually plan to put this back in, fixing the ABS will make that one step closer)
The height sensors on the front have been removed and the connectors were just dangling when I got the car - I just zip tied them out of the way but never insolated them.
Possibly could these open connectors cause a grounding issue? I know that the air suspension wiring runs close to all this ABS wiring.

Also just to mention :
New battery
New alternator
Wires run directly from alternator to battery
Cleaned pretty much all grounds apart from the really hard to get to ones (seems to be one under the center console etc) - all this fixed the dreaded "Transmission fault" - haven't got it now for over 6 months no matter what electrical load.

The brake fluid level is fine, the brakes feel good - nice solid (not spongey) pedal and easy to press.

I haven't bled the brakes since I got the car - I've changed the pump and installed a new accumulator without re bleeding the brakes, just clamped the hose on the reservoir - kept topped up with fluid when charging up again and it seems to have been fine - I don't think not bleeding the system would cause a grounding issue? It doesn't seems like it needs to be bled anyway...

Please let me know if there is anything else obvious I'm missing out on here,

Thanks!
 
Is the battery good and fully charged?
A healthy system with good accumulator should see 4 pedal purses before the pump starts.
No expert but i would expect the ref ground to be at our around 0v not 5v.
2 or 4wd TC?
 
kermit_rr said:
Is the battery good and fully charged?
A healthy system with good accumulator should see 4 pedal purses before the pump starts.
No expert but i would expect the ref ground to be at our around 0v not 5v.
2 or 4wd TC?
Click to expand...

Sorry, I should have mentioned - it’s a 1999 DSE so I would assume four wheel traction control.

I will count the presses tomorrow but I’d say it’s more like 3 presses before it runs / 2 presses the odd time.

The system should be fully charged, I no longer get any other voltage related issues since replacing all the normal stuff.

Yeah, I would think the reference ground should be around the 0 but tomorrow I’ll see if it changes when the engine is running / car moving.
 
MikeFl4 said:
Sorry, I should have mentioned - it’s a 1999 DSE so I would assume four wheel traction control.

I will count the presses tomorrow but I’d say it’s more like 3 presses before it runs / 2 presses the odd time.

The system should be fully charged, I no longer get any other voltage related issues since replacing all the normal stuff.

Yeah, I would think the reference ground should be around the 0 but tomorrow I’ll see if it changes when the engine is running / car moving.
Click to expand...

Yes, 4W TC. 2 presses not ideal but I don't think that is your issue.

The ABS ECU on the 4W TC models seems a lot more prone to faults. Marty_uk has picked up a few faults in the ECUs themselves although I cannot remember what specifically.

A couple on here have had issues so hopefully one of them will have a record of what the reference voltage is. Mine's on 2W TC so no help there.
 
From my limited experience you need to do 2 tests with a dmm on all 4 abs sensors. Unplug each one in turn and on the 2 pins, car side, you should get voltage , 5vdc iirc, ignition on. On the 2 pins, sensor side you should get resistance of circa 10,000 ohms, open circuit reading means dead abs sensor.
You will need 2 insulated probes to check the abs plug resistance, I used two pop rivet stalks with some heat shrink on them.
 
MikeFl4 said:
Hello everyone,

Just looking for some help on this issue please, since I have bought this vehicle its had a persistent ABS Fault and Traction failure message along with the two standard ABS and TC lights. They appear straight away once the I turn to ignition II and the ABS and TC light stay on the whole time.

I originally had a short on the front right sensor - bought a new one and this is now all happy.

I unfortunately don't have anything P38 specific like a Nanocom but I do have an Autel scanner - using this it can tell me:

All 4 sensors seem to be happy - they all show 2.3-2.4V and all output a speed signal (obviously only up to like 5kph since the ABS ECU stops communicating once you go faster - but they all read perfectly fine)

The main error code it gives me is : "ECU ground or Reference ground fault"

Intermittently I get : "Pump relay driver fault"

Also to mention - live data on the ABS ECU, there is a reading called "Reference ground" and this reads as 5V.

Things I've done:
New abs accumulator (this was weak anyway so needed to be replaced)
Cleaned all the related ground points E056X etc ones
Cleaned the connectors in the LH foot well - one of the wires was corroded to the point where its metal tab broke so I cut and soldered them together - others looked fine once cleaned but maybe I should just chop and solder all of them?
Swapped around ABS ECUs (I have a parts P38, I don't know if the ECU is any better in the parts car but its handy to have a second anyway - it still gives the exact same "reference ground" error)
Swapped around the ABS relay (from parts car), no difference.

Something I've noticed:
Even after installing the new abs accumulator - it still seems to take over 20 seconds to charge up - also possibly runs a little too often between pedal presses - I actually have two spare abs pumps (used, random condition) so maybe its worth just swapping one of these in?

Additional information:
The air suspension was removed from my P38 (I eventually plan to put this back in, fixing the ABS will make that one step closer)
The height sensors on the front have been removed and the connectors were just dangling when I got the car - I just zip tied them out of the way but never insolated them.
Possibly could these open connectors cause a grounding issue? I know that the air suspension wiring runs close to all this ABS wiring.

Also just to mention :
New battery
New alternator
Wires run directly from alternator to battery
Cleaned pretty much all grounds apart from the really hard to get to ones (seems to be one under the center console etc) - all this fixed the dreaded "Transmission fault" - haven't got it now for over 6 months no matter what electrical load.

The brake fluid level is fine, the brakes feel good - nice solid (not spongey) pedal and easy to press.

I haven't bled the brakes since I got the car - I've changed the pump and installed a new accumulator without re bleeding the brakes, just clamped the hose on the reservoir - kept topped up with fluid when charging up again and it seems to have been fine - I don't think not bleeding the system would cause a grounding issue? It doesn't seems like it needs to be bled anyway...

Please let me know if there is anything else obvious I'm missing out on here,

Thanks!
Click to expand...
The EAS connectors will have no effect on the ABS.
You need to bleed the brakes according to the procedure in RAVE the fluid in the modulator may be contaminated with water, but it will not cause a grounding issue. As well as earth points, there may be splices in the earth line.
There are differences in ABS ECU's was the one you swapped correct?
Best to cut out the white connectors in the left & right front footwells at the bottom of the A post, they are the cause of many problems. Solder and insulate with glue filled heat shrink.
 
Flossie said:
From my limited experience you need to do 2 tests with a dmm on all 4 abs sensors. Unplug each one in turn and on the 2 pins, car side, you should get voltage , 5vdc iirc, ignition on. On the 2 pins, sensor side you should get resistance of circa 10,000 ohms, open circuit reading means dead abs sensor.
You will need 2 insulated probes to check the abs plug resistance, I used two pop rivet stalks with some heat shrink on them.
Click to expand...

Would I have to do these tests? The scanner I'm using used to say "Front right sensor short to another sensor" - and it was correct as the wire was almost sliced through. Then after I replaced the FR I checked all 4 wheel sensors on the scanner - the rear right wasn't getting a speed signal, took the wheel off and gave the sensor a few taps - now all 4 reading consistently with voltage and speed.

Obviously I don't know whether the scanner is telling me everything, but I feel if it was a sensor issue it would have picked it up?

I have heard from a lot of people that the majority of the issues always come from wheels sensors, that you have to check and check again - so I can test each sensor and plug individually if you think its one of the most likely things :)
 
Datatek said:
The EAS connectors will have no effect on the ABS.
You need to bleed the brakes according to the procedure in RAVE the fluid in the modulator may be contaminated with water, but it will not cause a grounding issue. As well as earth points, there may be splices in the earth line.
There are differences in ABS ECU's was the one you swapped correct?
Best to cut out the white connectors in the left & right front footwells at the bottom of the A post, they are the cause of many problems. Solder and insulate with glue filled heat shrink.
Click to expand...

Thanks for the info on the EAS connectors, that was one of my worries as I do want to put the lump back on air one day, just need to sort out all the other issues first!

Ok - I will bleed the brakes - no harm to run some fresh fluid through the lines anyways.

Potentially the ABS ECU I swapped was different - That was only for testing as I put back the original - Ill dig it out again today and compare the numbers.

I will do the soldering today as I know that these wires are certainly not helping the situation - The RH footwell connectors looked great - would they need to be soldered as well?

I was thinking of trying to probe the ABS ECU connectors, find out which wires are supposed to be ground and.. well.. verify if they are ground! - I'm not really sure how to do this, I read that you should rig up a test light to the positive of the battery and then probe the grounds - when it lights up that is a confirmed ground.
 
MikeFl4 said:
Thanks for the info on the EAS connectors, that was one of my worries as I do want to put the lump back on air one day, just need to sort out all the other issues first!

Ok - I will bleed the brakes - no harm to run some fresh fluid through the lines anyways.

Potentially the ABS ECU I swapped was different - That was only for testing as I put back the original - Ill dig it out again today and compare the numbers.

I will do the soldering today as I know that these wires are certainly not helping the situation - The RH footwell connectors looked great - would they need to be soldered as well?

I was thinking of trying to probe the ABS ECU connectors, find out which wires are supposed to be ground and.. well.. verify if they are ground! - I'm not really sure how to do this, I read that you should rig up a test light to the positive of the battery and then probe the grounds - when it lights up that is a confirmed ground.
Click to expand...
It's worth doing the connectors both sides.
A test lamp is better than a DVM for what you want to do, a 5 watt lamp does the job connected as you say. Make sure the bulb lights brightly, dim = a high resistance connection.
 
MikeFl4 said:
Would I have to do these tests? The scanner I'm using used to say "Front right sensor short to another sensor" - and it was correct as the wire was almost sliced through. Then after I replaced the FR I checked all 4 wheel sensors on the scanner - the rear right wasn't getting a speed signal, took the wheel off and gave the sensor a few taps - now all 4 reading consistently with voltage and speed.

Obviously I don't know whether the scanner is telling me everything, but I feel if it was a sensor issue it would have picked it up?

I have heard from a lot of people that the majority of the issues always come from wheels sensors, that you have to check and check again - so I can test each sensor and plug individually if you think its one of the most likely things :)
Click to expand...
The fronts are easy to check, connectors are on the inner wing, compare voltage DC on the male pins and resistance on the female, then compare readings with the rear ones.
I'm no expert though but that's how we found a duff sensor on my mates, that had abs and tc lights on.
 
kermit_rr said:
Lights will come in if there's not enough pressure or the sensor/wiring is duff
Click to expand...
I definitely think that the pressure may be an issue - there is certainly some kind of a wiring thing going on as I do believe the scanners error codes.

I’ll check out the front sensors as I agree, they are so easy to access you may as well.

I’ll probe the ecu connectors once I find the needle tool!
 
Update: the grounds on the ABS ECU I could find are as following
I probed connector C504 pin 12 (Ecu ground) - and got a nice bright light
I probed connector C506 pin 3 (Reference earth) - nice bright light.

They seem to be the only grounds I could find in the workshop manual on the ABS ECU connectors.

I also chopped both multiplugs in the LH footwell, soldered wires and sealed. Didn't get around to doing them on the RH footwell as last time I checked these were actually in good condition.

Unfortunately it seems it’s not gonna be as easy as that, still the exact same issue.

As far as the ABS ECUs are concerned I have the pics below.
ABS ECU that is installed in the car (I dont know if its original - when I got the car it was missing one of the three bolts securing the ECU so we can only assume its been out before)
orig ecu.jpg


This what shows up when I read "ECU information" of the module on the scanner:
orig ecu scan.jpg


Here is the other module I have from a 2001 DHSE:
other ecu.jpg


I can see that the numbers are different on these ECUs, so I guess we can assume that they cannot be swapped.

Just for the fun of it, I plugged it in - This is what it shows on the "ECU information"
other ecu scan.jpg


Interesting how this one has a valid vin number where as the other one doesn't?

With this 2001 ECU installed - it initially read loads of errors - pretty much every sensor is shorted to another sensor ect - I cleared the codes and... yeah, the only error remaining was the good old "ECU ground or Reference ground fault" - It also displayed a 0v reading on the live data for the RL sensor - but I did not investigate as I assume all these errors were mainly caused by it being an incorrect ECU. Once I plugged back in the other ECU, it could read all sensors fine.

At a minimum, even if the ABS ECUs are not interchangeable - can we assume that the error "ECU/Reference ground" is probably not an internal fault in the ECU? Unless both the ECUs have the exact same fault, it must be an actual wiring/sensor issue.

I didn't get around to checking the sensors, but this is defiantly what I will spend my time doing tomorrow.
 
MikeFl4 said:
Update: the grounds on the ABS ECU I could find are as following
I probed connector C504 pin 12 (Ecu ground) - and got a nice bright light
I probed connector C506 pin 3 (Reference earth) - nice bright light.

They seem to be the only grounds I could find in the workshop manual on the ABS ECU connectors.

I also chopped both multiplugs in the LH footwell, soldered wires and sealed. Didn't get around to doing them on the RH footwell as last time I checked these were actually in good condition.

Unfortunately it seems it’s not gonna be as easy as that, still the exact same issue.

As far as the ABS ECUs are concerned I have the pics below.
ABS ECU that is installed in the car (I dont know if its original - when I got the car it was missing one of the three bolts securing the ECU so we can only assume its been out before)
View attachment 265825

This what shows up when I read "ECU information" of the module on the scanner:
View attachment 265827

Here is the other module I have from a 2001 DHSE:
View attachment 265828

I can see that the numbers are different on these ECUs, so I guess we can assume that they cannot be swapped.

Just for the fun of it, I plugged it in - This is what it shows on the "ECU information"
View attachment 265829

Interesting how this one has a valid vin number where as the other one doesn't?

With this 2001 ECU installed - it initially read loads of errors - pretty much every sensor is shorted to another sensor ect - I cleared the codes and... yeah, the only error remaining was the good old "ECU ground or Reference ground fault" - It also displayed a 0v reading on the live data for the RL sensor - but I did not investigate as I assume all these errors were mainly caused by it being an incorrect ECU. Once I plugged back in the other ECU, it could read all sensors fine.

At a minimum, even if the ABS ECUs are not interchangeable - can we assume that the error "ECU/Reference ground" is probably not an internal fault in the ECU? Unless both the ECUs have the exact same fault, it must be an actual wiring/sensor issue.

I didn't get around to checking the sensors, but this is defiantly what I will spend my time doing tomorrow.
Click to expand...

As far as I am aware all the 4W TC modules are interchangeable. The part numbers have changed over the years.

If the fault is the same with different ECUs then it does sound like a wiring issue. Where is the earth point in RAVE?
 
Grrrrrr said:
As far as I am aware all the 4W TC modules are interchangeable. The part numbers have changed over the years.

If the fault is the same with different ECUs then it does sound like a wiring issue. Where is the earth point in RAVE?
Click to expand...

If all the 4W modules are interchangeable, then I wonder why one module can read all 4 sensors - and the other one (2001 module) says that the RL is at 0v (either disconnected or short I assume)

I guess the 2001 module must be faulty unless there actually is an issue with the RL sensor - I will be investigating the sensors today.

The reference I was using for grounds - it’s kind of awkward to find rave as I’m away from home on my phone - it’s on the page as below:
B8901C61-EC15-4092-87DA-2296DD138C17.jpeg
 
MikeFl4 said:
If all the 4W modules are interchangeable, then I wonder why one module can read all 4 sensors - and the other one (2001 module) says that the RL is at 0v (either disconnected or short I assume)

I guess the 2001 module must be faulty unless there actually is an issue with the RL sensor - I will be investigating the sensors today.

The reference I was using for grounds - it’s kind of awkward to find rave as I’m away from home on my phone - it’s on the page as below:
View attachment 265859
Click to expand...
The common fault is showing error code 'short to another sensor' or not seeing a sensor plugged in.
Sounds like the ecu is faulty if another sees the sensor ok
 
If the ECU is duff classic rides north Wales have check known ECU's for £75 which is not atall bad for the 4wtc ones alot of places want 120.
 
kermit_rr said:
The common fault is showing error code 'short to another sensor' or not seeing a sensor plugged in.
Sounds like the ecu is faulty if another sees the sensor ok
Click to expand...

Yes, my second ecu has trouble with some of the sensors, but the first one seems to be fine. I will investigate the sensors and see if they actually are fine - then decide whether it requires a new ecu
 
brianp38dse said:
If the ECU is duff classic rides north Wales have check known ECU's for £75 which is not atall bad for the 4wtc ones alot of places want 120.
Click to expand...

Yes, I’ve been in contact with Les a few times, I’d definitely go to them if I need any ecu work done.
 
Hello everyone, thanks for all the suggestions so far, really it’s all I’m looking for as I just have to try stuff!

I haven’t got a chance to measure each individual sensor but I did hop in this morning and record a vid. ( they’re actually 2 vids I can’t seem to combine them into one on my phone)
https://youtube.com/shorts/c5JK8j85rDs?feature=share
https://youtube.com/shorts/Gm4sCVw7hWU?feature=share
It shows the output im getting on the diagnostics, vehicle already started up. As we can see there is a steady voltage reading on all sensors, this then fluctuates when I drive (slowly) - then the speed reading, they all read in and around the same speed.

I’m still going to go through the motions and check out the sensors, but I feel if it was a bad sensor surely it wouldn’t be working?
 
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