Citroen XM Forum

I never realised those rubber hosey bits were part of the water system on the car! Now we know!!
Good news, Russ.

Tell me about it. Water had got into the hose and filled the back of the plug. It had rotted out the pin to the puddle light. The wire completely snapped off and the pin left in bits in the plug. All extracted now and repinned. Back to normal service, locks working and the puddle light shining brightly. Cleaned up and protected the other side for good measure too.

Nice day to change the ignition switch.... to 1. Get my old flip key back, and 2. See if it fixes a strange issue with the blower being a bit intermittent, and the Rev counter needle flicking about like a nutter. Infact it got so bad it gives up, then springs back to life and behaves. Odd. Oh and also driving along, this has happened three times now, suddenly I get AUTOMATIC SUSPENSION come up on the LCD screen for no reason at all.
Anyway, unfortunately switching over the ignition switches hasn't fixed either issues. But I do have my key back!

So back to square one. And possibly as Paul has suggested, changing the TDC sensor..... Once I have located it!
But with the other strange goings on, I still feel they are connected somehow, but no idea how.

it could be a poor contact int eh Crank sensor lead, I've fixed that on a Xantia a long time ago...but the "Automatic Suspension" alert is suggesting a poor +ve feed to a number of circuits.

Check all the leads and conenctions that are fed from ignition fed source.

I have found quite a bit of info suggesting the crank sensors do go on mk2 Bx's, Xantias and clearly XM's.. All appear to be XUD. Wether that's relevant or not who knows.

Thanks Will... I'll re check all positive feeds. It does seem like that's the probable cause.

An update on the unusual electrical issues.

The cars Rev counter goes nuts from time to time. Having located the plug, very easy, didn't realise it was right where it was, I cleaned a tiny bit ofcorrosion off one pin, but gave them all a good spruce up and wd40 it, to see if that might cure the issue.
I have also, with a handy suggestion from John, to find a white connector under the dash (it should feed power to the LH matrix and the Rev counter) and see if it has worked its way loose. On Friday the car refused to show up any of the messages on the LH dot matrix and no suspension pressure warning lights either. Until I got to the end of the road and everything woke up. Rev counter all over the place still, infact the worst it's been.
Today I went connector hunting in the drivers foot well. All the plugs seemed secure. Pressed them together to make sure incase they had just worked themselves loose.

This afternoon I took it out for a good run and the messages on the dot matrix are working fine. Back to normal. Initially the Rev counter was behaving. But got stuck in traffic and it started bouncing about again. However it does seem to have boughts of working fine, then goes a little haywire and then back to normal. So unless there is another unknown plug somewhere, it looks like a new TDC sensor is needed. Knowing there are two types of sensor, I found its location, completely hidden ontop of the flywheel. But at least it is the version that has a 10mm nut and not the one you have to guess the depth it goes in by.

Having said that though, how on earth you get to the blimmin thing I don't know. Triple jointed alien fingers most likely! No wonder Haynes doesn't mention it. I can imagine the procedure. Disconnect battery and remove engine. ERGH! I am so cross I didn't change it when the engine was out. What do they say about hindsight.....

Did try to locate a circuit diagram for #160 TDC sensor on your S1/5712, Russ, but I don't have. John might have to help again.

What else is the TDC sensor feeding?
On later cars, it's also engine ECU (with the rev counter driven off the ECU), so you'd expect there to be engine issues too.
Also, from the diags I do have, TDC sensor output is available directly at the diagnostic socket, so would facilitate testing.

You'd be looking at Section 51 of the Circuits manual, if you have it.

Thanks Chris,

To my knowledge the 2.1 of my era, doesn't have an engine ECU. All mechanical. There be a great big empty space where one would be in the ECU box! The engine is performing great. No obvious issues there. So all I can assume is it directly feeds the tacho. Single plug from the sensor that feeds right into the main wiring loom to the main connector under the LHM tank and then into the car.

I'm sure it's just worn out. Not looking forward to trying to replace it though.
What is frustrating me is working out why the other issues have occurred. So far all the connectors in and around the dash are fine.
One last thing to do later when it gets darker is to check the back lighting to the dash binnacle. I have a suspicion it's stopped working for some reason. If it has, it might be a clue.

Yes, mechanical. Had to think back to BX/XUD9 days.
Speed sensor will have two wires to it, GND and Output. GND ok?
Continuity of Output cable to instrument (I'm assuming nothing in between)?
What resistance is the sensor itself showing (ohm-meter straight across it, not connected to anything else)? These sort of sensors normally about 1k ohm.

Tacho instrument itself will probably have four connections.
1990 Haynes XUD9 manual shows direct 2-wire connection from sensor to tacho instrument:
+12v IGN sw
GND
TDC sensor output signal
TDC sensor GND

If wiring between sensor and instrument is suspect, you could temporarily run a piece of screened cable to connect the two, screening to GND side at each end, just to test. (These sort of sensors don't usually mind which connection pin is GND'd, so long as one of them is.)

Spent this morning cleaning and making sure all the connectors, including those under the LHM tank, and suspension ECU plugs, speed sensor ect, I can lay my hands on are secure and not corroded. All were fine.
Also cleaned all the earths, made sure they were tight. One was a bit loose for some reason. Probably failed to nip it up at some point. Swapped back to the old positive battery connector and cleaned and greased both connectors to make sure they are fine.

So time will tell if the odd Automatic suspension dot matrix message pops up again mid drive.

But the one thing that is still flicking about is the Rev counter. So for me that's it. New sensor needed. Can't be anything else as far as I'm concerned!