Citroen XM Forum

Make sure the diode in the relay unit is functioning properly and has continuity in one direction.
Check there is power being supplied to the relay via F3 in the engine bay fusebox and the relay has a good Gnd.
Does the lamp go out when you trigger the relay manually?

If the controller isn't pulsing the relay, then it has to be a controller, or power input issue.

Nice strip-down of the diesel pump, all the way to the vane pump. You can replace the metering head O ring without removing, or dismantling, the pump; simply remove the injector pipes and loosen the metering head enough to sneak the O ring out and a new one in.

Always make sure your (wheel) nuts are done up tight enough. It will always be the front left comes loose due to the bolts being Rh thread.
I always leave the covers off until torqueing the bolts. 90Nm for Xm steelies, 100nm for alloys.

Dieselman wrote: Tue Apr 29, 2025 6:44 am Make sure the diode in the relay unit is functioning properly and has continuity in one direction.
Check there is power being supplied to the relay via F3 in the engine bay fusebox and the relay has a good Gnd.
Does the lamp go out when you trigger the relay manually?

If the controller isn't pulsing the relay, then it has to be a controller, or power input issue.

I've double checked my work today, the diode is good. I've got power and earth at the pins which they should be present on throughout the ABS system.

However, I've done more testing of the wires from pins 19 and 8 on the ECU, which go to the relay coil. I was measuring about 2.5v at pin 3 on the solenoid end of this loom - obviously not right. I then unplugged the ECU, and I was seeing this voltage rise to 4.5v. I can measure this at either pin 19 on the ECU connector or pin 3 at the solenoid connector. On pin 8 at the ECU connector and pin 2 on the solenoid connector I am reading 2.5v

Considering that the wiring diagram shows these as direct wires with no other splices, the only conclusion I'm coming to is that the loom must be damaged somewhere and I'm seeing a short between these wires and other circuits.

I've removed most of the loom and will start stripping it back and checking it over the next few days.

Nice strip-down of the diesel pump, all the way to the vane pump. You can replace the metering head O ring without removing, or dismantling, the pump; simply remove the injector pipes and loosen the metering head enough to sneak the O ring out and a new one in.

Thank you - I did strip it to a bare housing, but forgot to take a photo of this stage. I actually found it very enjoyable to strip and rebuild, I like jobs like that, I'd happily do that job again rather than continue to work on the ABS wiring.

I did consider swapping the o ring in the way you suggest, but I've had a series of leaks from this pump and decided that it was for the best to swap out every seal for new. I was already doing the timing belt, so it wasn't much extra work to remove the pump.

Always make sure your (wheel) nuts are done up tight enough. It will always be the front left comes loose due to the bolts being Rh thread.
I always leave the covers off until torqueing the bolts. 90Nm for Xm steelies, 100nm for alloys.

I do the same as you - I only put my wheels back on when I have the torque wrench at hand, and fit covers once the nuts are torqued. what went wrong here was I pinched the first bolt on the outside of the seat on the steel wheel by hanging the wheel from it when struggling in the dark, and it didn't self centre as the others went on. The first time I checked it, there was no play in the wheel or the bolts, but I took it for a couple of laps of the block (it's a dead end here, so quiet and mostly safe) and then as you rightly predicted it was the front left wheel that gave the game away; a couple of the bolts backed out slightly at this point. I have one of those threaded rods for seating wheels that use bolts, so I've now made myself get into the habbit of using that rather than trying to hold the wheel in place with one hand whilst threading bolts with the other and swearing.

Looping back to the subject of hard/slow starting, I've now replaced the negative battery cable, added a relay to the starter solenoid circuit, and I've replaced the glow plug wiring with suitable wire. The car still struggles to start, despite cranking healthily now. I guess the last place to look is the pump timing - I've started playing the game of tweaking the pump back and forwards earlier today, to try and see if I can improve it. I will double check the fuelling adjustments on the pump too, just in case.

On the subject of electrics, I note that even with the starter solenoid circuit interrupted, the colling fans run when I put the ignition to the 'start' position. That's definitely not right! I was thinking a bad earth at first, but if I'm breaking the circuit to the solenoid and it isn't being energised then that's now leading me to believe that there's a short in the loom for the fans somewhere. I also can't help but wonder if this is related to my issues with the ABS wiring.

josh2109 wrote: Tue Apr 29, 2025 9:46 pm Considering that the wiring diagram shows these as direct wires with no other splices, the only conclusion I'm coming to is that the loom must be damaged somewhere and I'm seeing a short between these wires and other circuits.

I've removed most of the loom and will start stripping it back and checking it over the next few days.


I did consider swapping the o ring in the way you suggest, but I've had a series of leaks from this pump and decided that it was for the best to swap out every seal for new. I was already doing the timing belt, so it wasn't much extra work to remove the pump.

I pinched the first bolt on the outside of the seat on the steel wheel by hanging the wheel from it when struggling in the dark, and it didn't self centre as the others went on.
I have one of those threaded rods for seating wheels that use bolts, so I've now made myself get into the habbit of using that rather than trying to hold the wheel in place with one hand whilst threading bolts with the other and swearing.

Looping back to the subject of hard/slow starting, I've now replaced the negative battery cable, added a relay to the starter solenoid circuit, and I've replaced the glow plug wiring with suitable wire. The car still struggles to start, despite cranking healthily now. I guess the last place to look is the pump timing - I've started playing the game of tweaking the pump back and forwards earlier today, to try and see if I can improve it. I will double check the fuelling adjustments on the pump too, just in case.

On the subject of electrics, I note that even with the starter solenoid circuit interrupted, the colling fans run when I put the ignition to the 'start' position. That's definitely not right! I was thinking a bad earth at first, but if I'm breaking the circuit to the solenoid and it isn't being energised then that's now leading me to believe that there's a short in the loom for the fans somewhere. I also can't help but wonder if this is related to my issues with the ABS wiring.

A loom issue sounds plausible.

For the fuel pump seals to all leak suggests it has been run on veg oil at some stage.
Poor starting:
Compression, glow-plugs, pump timing and cold start accelerator and timing advance functions, air leak into fuel system.

Wheel fitting. No need for an alignment stud, just place your hand on the outside of the tyre and constantly rock the wheel as you are tightening the bolts past 3/4 of the way in: the wheel will constantly self centre.
I lift and place the wheel on the spigot, hold it on with my left hand near the centre, grab a bolt and loose tighten it with my right hand, then place all the bolts, while rocking the wheel.

Cooling fans coming on indicates an issue with the Bitron fan control, either the controller, wiring, or sensor fault.

I’m hoping that once I’ve unwrapped the loom, I find some obvious damage. I really want to get this ABS issue wrapped up so that I can get the car back together.

It could well have been run on veg at some point, I have no history for the spare pump but it was very waxy and varnished inside - earlier in the thread when I fitted it, the governor wasn’t working properly as it was not free to move.

The cold start advance definitely doesn’t work, sadly on both of my pumps this waxstat is broken. I could pin the arm back though, I guess. Likewise with the fast idle. I’m confident that the fuel system is now airtight.

I have some weakness in both arms due to injury, so I find the alignment stud helps in that I don’t have to support the weight of the wheel - I struggle to even hold the wheel on the spigot otherwise. But appreciate what you’re saying.

I’ve been digging around for the Bitron box but can’t find it - it’s not under the dash on the passenger side, so will pull the driver’s side apart next…

I forgot: for the cooling fans to be stuck on low speed, it could just be the relay has stuck closed, possibly after a low voltage situation has caused arcing.

Right, I'm very much overdue an update!

Good news - I've found the issue with my ABS system. This connector beside the fusebox had broken down inside and is producing a very high impedence:



I only discovered this by back-probing the loom at the ECU end, and I could see the voltage was collapsing when the circuit was made. I checked and confirmed this by making up a test lamp and using it to test the power feed with the ECU removed: +12v without a load, 0v when under load. I then made a jumper lead so that I could provide +12v to the ECU to test there weren't other issues, and with the jumper lead everything worked.

I've cut out the old connector, and replaced it with a new waterproof connector.

The ABS light now comes on, shows the self test flickers, then goes out. It's nice to not have that lamp permanently lit up anymore!



The only downside is that I started looking for issues at the fusbox end (I can't recall why, there was some sort of reasoning at the time) and so that was a faff to reinstall.

I found the Bitron box in the driver's footwell. I disected it, and found that one diode was scorched and a few others are dead



I'll try and get round to removing and replacing those, although annoyingly the scorched one is under the legs of the connector.



I then finished putting the timing covers back on, engine mount, and cooling hoses, radiators etc. that I'd removed when following the wiring loom. After that I filled the coolant:



This would have been a perfect job for my spill free funnel, but my son broke the funnel part when I left it in his reach a while back. Luckily the adapters were still usefull, and the bedge job I made from those and another funnel didn't leak that much.

The bitron box is temporarily installed, and I ran the car up to operating temp to let it self bleed.



All seems good now - the new thermostat has made a brilliant improvement to the warm up time and running temperature of the car.

1 in 4 chance of getting the worst side of this thing pointing the way you don't want it, and somehow even when I make note to pay attention I get it wrong. It's now been turned to the most 'enthusiastic' side.



I've had to advance the pump to about 3/4 of the way through its movement, and now the car start fairly reliably. I do think it's too far advanced though, as I'm sure I'm getting some diesel knock. It needs some more fiddling to get right, I'm wondering if the collar on the fuelling screw has slipped as I recall adjusting this to add more fuel did help with the starting before.

There we have it though, a happy car with a clear dashboard for a change:



Albeit not for long.





The offside front brake pipe burst on the way to work the day after the car was 'finished'. I limped it home using the parking brake where practical (I was only about half a mile from home). The pipe must have been at the end of its life anyway, and my work in the vicinity has tipped it over the edge.

I've put the car back on stands and I've started stripping the old brake line off, and will replace it over the next couple of days.

I have come to a conclusion though: I'm at the end of my journey with this car, and it's time for it to find a new home. I have a lot of other projects which need attention, and I also have an upcoming move of my storage. Originally I was holding on to this as I knew I'd never see my time investment back from it (I think I'm at about 500+ hours now), and the idea of selling it and never seeing that time back was a bit gutting. Now my time is far more important and needed elsewhere, so letting it go and losing out on the time (and money) spent doesn't feel so bad anymore. I'll get a post in the correct forum up once the brake line is replaced, but I'm hoping for £750 for it which I hope isn't unreasonable for an XM that will be ready to drive away.

I'd like to say a big thank you to you Dieselman, your knowledge of these cars has been immensely helpful, and in all honesty without your input I think I probably would've given up on this car a fair amount of time ago and it possibly wouldn't have seen the road again. If we ever cross paths then I certainly owe you a drink or two!

Good news it's pretty well all fixed, which is the time to enjoy the fruits of your labours. You have been catching up on years of neglect, have another think before giving up on it.

I’d keep it if I didn’t have any other financial or time pressures at the moment, but I need some money back in and I also need to spend time on other commitments. I’ve enjoyed the XM during the times it has been working, but I’m definitely at the end of my journey with it now.

That said, I of course have to sort out the blown brake line. I got the old line out this evening, and made up a length of brake line to 2.4m which was what the part catalogue suggested. I then started from the ABS pump, and bent the line in situ. Not the prettiest, but it used the factory clips where they are still present. I had to lose a bit of length at the calliper end, but there are no clearance issues fortunately.




Despite taking care, the bleed screw on the calliper sheared.



Welding did not save the day, sadly.




Surprisingly, patient drilling did save the day.




It must have known that I’d got a quote from cartakeback after the bleed screw sheared

I’ve had a couple of beers to celebrate, and I’m absolutely exhausted. Hopefully I can get a bleed screw in tomorrow, get the brakes bled and get the car mobile again.

Nice job on recovering the bleed screw.
I'm not surprised it sheared, it does look pretty rusty. Maybe giving it some heat, a few hammer taps straight down, or inserting a drill bit prior to unscrewing, may have helped.

Thank you, it was a relief once I got the screw out and saw that there was no damage to the calliper.

The access when the calliper was fitted to the car was poor, I did try to get some impacts on the screw before undoing it but I just couldn’t get much of a shock into it. I gave it a belting with a punch before I welded a washer and nut on it, and nothing was shifting it; I think I was set to lose from the start on that one.

My partner is picking up some bleed screws for me on the way to visit her friend, so hopefully I’ll have this sorted after work today.