Citroen XM Forum

I've never heard of this issue previously and mine doesn't always do it.

When I get the rest of the issues sorted I'll have an in depth look and report back.

My observations the same as yours, the guage starts by working properly then after a predetermined time flicks to Full and the warning flashes. I first thought the time factor was possibly in response to the Hydractive valve timing, but don't think that's an issue now.
Have you tried reading the engine fault codes to see if there is any information to be gleaned?

Hi Phil,

Very odd that the Low Fuel Level warning light operates at the same time as the gauge reads Full.
Did take a look at our Y4 owner's handbook, and Low Fuel light is only referred to as coming on continuously, indicating 8 litres of fuel remaining. No mention of a pulsing light.
Could be that the pulsing is indicating a system fault: tank sensor + instrument panel p.c.b.

The tank float-sender unit is a potentiometer (3 connections: supply voltage, Gnd, output voltage) and not just a series resistance. Possible that one of these connections, or the unit, is going open circuit, and so sent voltage jumps high. Worth checking associated Ground connections.

Gabor's circuit diagram for the XM (Y4 2.5, but broadly applicable) could help. Download it here:
viewtopic.php?f=13&t=7592&start=50#p105940

Gabor has also closely examined a fuel tank sensor (in chasing different fault). You might find it interesting.
See p.5 of the thread onwards:
viewtopic.php?f=8&t=7171&hilit=fuel+rhe ... =20#p95572

The fuel guage suddenly swinging to full and the light flashing is a random occurance, but not a random effect. Something is definitely triggering it to happen.

Id say its the small pcb converter board buried in the speedo clocks.. the level sender is NOT directly attached to the level guage.. it goes to a small pcb first before going to the guage to convert the signal and also regulate the needle level on the dash.. otherwise the guage would be up and down swaying everytime you go round corners..

The xantias are the same and the pcbs pack up.. ive changed a couple of xantia ones but not xm ones.. im fairly sure they are the same setup idea..

citroenxm wrote:Id say its the small pcb converter board buried in the speedo clocks...

I would think you are correct. Of course I recently let my my spare one go to someone that wanted an automatic gear selection display...

I have oodles of speedo clocks Will... and anyone else.. so if anyone needs one..

If the car has remaining miles display, the pcb is completely different and not interchangeable directly. Also, the functioning is different. Without autonomy display, the fuel gauge is connected almost directly to the sender (there is some small circuitry involved but not much), as is the low warning light. With autonomy display, it's controlled in a much more computerised fashion (eg. the warning doesn't come on with a specific fuel level but when the computer calculates the renaming autonomy to be below a specific value).

Thanks for the very helpful comments.
Is the PCB convertor board in the right hand display, which has the fuel, water temperature and oil level gauges? I am guessing that it is buried in this unit rather than the speedo.
Thanks again for the help.
Phil

Yes, exactly. I'll look up the topic where it was discussed and shown.

viewtopic.php?p=101622#p101622" onclick="window.open(this.href);return false;

Message #83 has the pictures of both panels. The panel, the fuel sender and the wiring in between are different depending on whether you have autonomy display or not. The gauges themselves are the same.

Wait a minute, I saw that flashing, only I can't remember now. That topic described my project of retrofitting the autonomy display (I had the trip computer without it before). Let me think. I replaced the panel and the fuel sender. Then I realised that wasn't enough, I had to adjust the wiring, too. But that doesn't apply to you, you have all that already. During all those operations I did have flashing at some stage. I'm not sure now but I think it flashes when you don't have the fuel level sender connected. It doesn't simply show no fuel, it's cleverer than that. The simple setup (without autonomy) only uses two pins of the sender, so an open circuit is simply shown as no fuel, warning light on. But the complex setup has three pins and can determine the presence of the sender independently from the level.

So, with that in mind, I'd check the connection from sender to the gauges first. The sender is obvious and easy under the seat. There's a connector in the right sill, you might leave that as the last step. The wiring connects to the piggy-back panel (green connector) of the instrument cluster. I would go in this order, if it isn't the sender connector itself, remove the panel and check for bad soldering (or resolder the connectors without checking, that only helps in the long run). Only go on if this doesn't help.

Thanks for the additional info Gabor.