P38 ABS Fault Question

Hi All

I have a 1997 P38 4.6 V8 Auto which I've owned for about 5-6 years now. Was initially used as a 'skip' for a building project we had and has now become a much beloved 2nd/3rd vehicle that we aim to keep for as long as we can and actually look after more now than we did when it was used as a skip. The battery went flat and then kaput as it didn't get used during lockdown so I recently replaced that. Not sure if that fact is related to the issue but seems all ok except that the ABS light now doesn't go out once you move off and get up to speed as it should and in fact we get an additional 'ABS Fault' message popup on the dash just after turning on the ignition.

I have an Bearmach Hawkeye diagnostics box and connected that up and when checking the ABS on there it tells me 'No power at ECU Pin 1 when ignition is on' - I tried clearing the fault message but on restart same 'ABS Fault' again shows on dash and on reconnecting the Hawkeye the same 'No power at ECU Pin 1 when ignition is on' fault is back.

After searching online and in the forums I have checked all the relevant fuses and relay's which all appear ok and have even tried replacing these just in case and still no joy. I found and removed the ABS ECU box which on the face of it looks like it should be ok but as its a sealed unit its hard to be sure although from reading online I think its the 99 models onwards where this ECU sometimes goes wrong.

On checking the plug harness that goes into the ABS ECU I located what is pin 1 and put a meter on this and while some of the other pins I can get a reading on it does in fact appear that there is no power at pin 1 as the Hawkeye is suggesting. If the relay's and the fuses are ok I'm guessing the only other likely issues are going to be something wrong with the actual fusebox or there is a break somewhere in the pin 1 cable from the fusebox to the harness that goes into the ECU.

My next course of action seems to be to get the fusebox off and test it and / or replace it and see if that fixes the issue. If it's a break in the cable somewhere then I suspect that's going to be a real PITA to fix.

I'm turning to the greater knowledge of the forum to verify if my troubleshooting route is correct, whether anyone has come across and solved an issue like this before or whether anyone has other ideas for me to look at. The rest of the ABS system 'seems' to be running ok and not reporting issues in the diagnostics but who knows with these little beasts if its something else and the errors I'm getting are misleading me?

I did read somewhere that after a time an ECU can record a hard fault and it needs a certain type of diagnostic unit to clear that. I thought from research when I got the Rangie that the Hawkeye was one of the best home diagnostics to get for these aside from the ones the dealerships use, but could that be my issue in that my Hawkeye isn't able to clear this 'hard' fault?

All help appreciated. MOT is due so I need to get this fixed if I want to keep this Rangie on the road longer.

Thanks
Chris.

Check behind the left hand a post panel there is a couple of white multi connectors these suffer water damage the answer is to cut the wires one buy one and solder and heat shrink, that would be the first port of call the EAS also goes through there.

+1 to that suggestion. To solder and heat shrink is the way for that junction block.

brianp38dse said:

Check behind the left hand a post panel there is a couple of white multi connectors these suffer water damage the answer is to cut the wires one buy one and solder and heat shrink, that would be the first port of call the EAS also goes through there.

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OK thanks I will get that panel off and check those multi connectors. EAS (touch wood) is all working fine.

Have you checked both f24 and fuse maxi n°2 in the fuse box?
Also try another relay.

Mark Piercy said:

Have you checked both f24 and fuse maxi n°2 in the fuse box?
Also try another relay.

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Thanks, but yep, tried both swapping the relay with another similar one in the fusebox and with a spare I had lying around and with a new one I bought on the weekend. I know these relays can be temperamental but with all those permutations I would have thought Hawkeye would have recorded some other faults if there was a bad relay there. Checked and double checked all the F fuses related to the ABS system as well as the maxi one.

Hoping to have some more time on it tomorrow or Friday when I will lift up the fusebox to see if I'm getting any power out of the relevant connection from there and see if there is anything obvious looking wrong there and as suggested above take off the A pillar and check the connections there. Will report back my findings....

Can you trace the abs ecu power wire back to the fuse box?
If so à continuity test should reveal a break. If it's as simple as that.
I'd look for output from the fuse box plug that goes to the abs ecu and then look at the contacts. Presuming you can trace the wire and there are no colour changes along the route...

So had some time on the car today. No joy in resolving the problem. What I think I have established is I don't think there are any breaks in the wiring and I think the fusebox is ok. For the RL2 relay I established that there is voltage coming through the relay when it engages and I can measure this same voltage at the connector to the ABS ECU. My only issue with this voltage is it seems quite low at 0.3 volts, although if I also measure the other side of the relay this is the same voltage coming into that route. I'm trying to understand from the various docs I've found online if this voltage is correct or its my problem. Is there anyone here who understands the wiring here better than I can so far interpret to confirm whether this is the voltage that should be going to pin 1 on the ABS ECU?

Apart from the above I'm at a bit of a loss as to what to try next. I guess I could try to swap out the ABS ECU to see if that has a fault. Or could it be something else in the ABS system that is at fault and my Hawkeye is giving the wrong fault code?

Can anyone recommend a P38 knowledgeable garage in the Somerset area (Near Weston-Super-Mare) who might be able to help? I don't mind spending a bit of cash to get it this fixed as everything else with the car I'm happy with and seems functional so it would be a shame to have to have to take it to the knackers yard because it can't pass its MOT because of this.

just a thought as had same on mine I done a live drive test and found one side not working so got back and swaped the ABS sensors around left to right and visa versa if it could narrow it down to faulty sensor

I would have thought 12v at the ecu live pin for that age of car?
Have you checked the voltage through the relèvent fuses also?
It could be a fault in the fuse box..

Karlos the jackal said:

just a thought as had same on mine I done a live drive test and found one side not working so got back and swaped the ABS sensors around left to right and visa versa if it could narrow it down to faulty sensor

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By the same do you mean getting the ABS Fault error on the dash or getting the no power at pin 1 on the ECU error from diagnostics? If it was a faulty sensor then I would have expected Hawkeye to report that, but willing to try anything to resolve the issue. MOT has expired now so technically shouldn't take it on the road unless on way to a test centre but will see about giving this a go - thanks.

Mark Piercy said:

I would have thought 12v at the ecu live pin for that age of car?
Have you checked the voltage through the relèvent fuses also?
It could be a fault in the fuse box..

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Yes, I thought 0.3v was a bit low. From doing more reading and searching online I'm suspicious of the fuse box and / or the battery connections. This whole problem started after I installed a new battery after the old battery went flat and wouldn't recharge. The 0.3v does seem like there may be some resistance in that circuit. I will check and clean the battery connections but I would have thought if it was that then I would get more errors than just the ABS one. Looks like a new fuse box is around £120-£130, could be worth a punt. There are second hand ones on ebay but guess risking there that they have a fault in them.

You could really do with finding the wire coming from the fuse box for the abs ecu and checking the voltage there, then connect your multi meter/dvm to the fuse box abs ecu power and then to the abs ecu pin1 and turn to 12v and check if there is a voltage drop between the fuse box and the ecu. If there is resistance in the wire the difference in power will run through the meter and expose a possible problem in that area.
Have you also tried swapping out the fuses for a substitute.
The fuse boxes are particular to that model and you need to match the numbers inside the fuse box lid like for like or it may not be rigged with the same facilities as your own.

Sensors pushed in all the way? I don't think diag can see output from sensors pre-99 but might be wrong.

Full brake bleed is cheap. How soon does ABS pump switch off after startup and how many presses or pedal before it runs again?

Chrisnj said:

By the same do you mean getting the ABS Fault error on the dash or getting the no power at pin 1 on the ECU error from diagnostics? If it was a faulty sensor then I would have expected Hawkeye to report that, but willing to try anything to resolve the issue. MOT has expired now so technically shouldn't take it on the road unless on way to a test centre but will see about giving this a go - thanks.

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I had abs light in dash would go off so did live drive and found left on not working so swapped with right side then hawkeye said right side not working so narrowed it down to sensor was faulty

Grrrrrr said:

Sensors pushed in all the way? I don't think diag can see output from sensors pre-99 but might be wrong.

Full brake bleed is cheap. How soon does ABS pump switch off after startup and how many presses or pedal before it runs again?

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I'll double check the sensors are pushed in, tempted even to add new ones of those to the list of things to work through replacing and seeing if it resolves the issue if I can't find anything else. Like I say I would like to keep this one going but looking around I think the brakes could all do with a refurb (new pads / disks) and a clean up, so maybe a full overhaul of the brake system is in order, although new fusebox is currently first on the list to get replaced. I did some further tests today and what I think is the fuse feeding the relay for the ABS ECU also shows the 0.3v I'm getting at the ABS ECU pin 1 although some other random fuses I pulled showed the full battery power, so either this voltage is correct or that particular part of the fusebox has an issue.

On the ABS pump it must have taken 40-50 seconds to stop when I first started from cold this morning (can't be exactly sure as didn't time it) now if I leave it for 10-20 mins or so and then startup it runs for about 5 secs and stops. activates for a couple of seconds every time I press the brake pedal. Could this be an indicator the pump and or the accumulator also need to go onto the replacement list?

I'll try a brake bleed next as you say its cheap.

Just focus on the ecu fault. A low voltage is the first thing to deal with.
The brake pump will kick in before you manage to do four presses of the pedal if the sphère is buggered.

Update on this issue...... Sadly still getting the ABS Fault error coming up on the dashboard :-(

Replaced the Fuse box this weekend. Also replaced the Accumulator while I was about it as it was displaying issues (pump kicking in every time I pressed the brake pedal) and it was very easy to get at with the fusebox removed. Where I was getting the 0.3v readings from the fuse in the old fuse box I am now getting the full 12v. Except from the RL2 relay when it activates and feeds down to the ECU plug. Really weird, I've tried several relays in that spot and all still give the just 0.3v even though the live side reads 12V - could I really have that many faulty relays? I've tried others already in the fuse box as well as new ones I've bought. Admittedly the new ones are OEM or after market ones. I've ordered one more relay, a genuine LR one, to try as well just in case. But very bizarre.

I think I've discounted the wiring loom from the fuse box to the ECU plug as I rigged up a jumper to simulate the relay working by jumping the live pin (where I get 12v) to the pin that feeds the ECU plug and when tested at the ECU plug I'm getting the full 12v reading there so that points to it being the relay that's my problem but don't understand why. I must have tried about 6 different relays in that spot - can I be that unlucky that all these relays have issues??? Will find out when I get the new genuine LR part relay if that too fails....

I've also ordered a replacement 2nd hand ECU off ebay just in case. I know if its second hand it could have issues but its only £20 and worth a go just in case.

If neither the genuine LR relay or the ECU fix it, then next on the list is a brake bleed as Grrrrr suggested, then I'm onto replacing the sensors and while I'm at that I may as well replace the discs and pads. Any other suggestions gratefully received. This issue is being a right PITA to fix but the Rangie is getting a good overhaul in the process!

Will keep updating this thread as I go if its not annoying everyone as if I do get to fix this it may prove a useful guide to anyone having a similar issue in the future.

When you placed a jumper wire was there still an abs fault?
If it relates to an internal power/system fault it may need clearing after the power has been restored to the ecu. Remember the abs is a critical system and won't necessarily ignore a power related fault.

Mark Piercy said:

When you placed a jumper wire was there still an abs fault?
If it relates to an internal power/system fault it may need clearing after the power has been restored to the ecu. Remember the abs is a critical system and won't necessarily ignore a power related fault.

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No I didn't connect the ECU when I jumped the relay as all I wanted to test was that the wiring down to the ECU was not losing voltage. I wasn't sure if it was safe to connect to the ECU like that with the relay jumped but the more I think about it I guess that should be ok. Will give that a try next weekend when I get to have another play on it.