Citroen XM Forum

Making good progress there - it all helps! Are you going to change the mirror switch as well?

Don't know if it is worth a try but a hot air gun can sometimes work well on faded plastic. Maybe worth a try before you swap out the switch?

I've already swapped it once lol.. I didnt think the morror switch needed a change. .it works.. the ones i all have all have what look like cracks in them .

Ooooo ... on my phone anyway.. I didnt realise if I click the pictures a much higher resolution picture loads up..

Back on track... slightly I retrived a fuel pump from my stock, however its a 4 pin setup..

It appears theres two types of level senders fitted and they are wired slightly differently..

Inside the sender the 5 pin has all three wires for the level guage wired to separate pins plus power for the pump, but on 4 pin level senders, theres still 5 wires but the black is joined to the brown iirc.

This however is not affecting the car starting and running however it is now making the fuel guage goto max and the low level lamp to flash.. so.. the two level senders 4 and 5 pin are shown in the wiring diagram to.. so I'm not sure what I can do to rectify the issue.. diagram attached if it helps work it out...
I wonder if I join pin 5 to pin 2 on the ribbon it would work..

Looks like the 5 pin has a seperate wire for the "low fuel" lamp, while the 4 pin just sent the level (and I guess the ecu calculated when to switch the lamp on?)

^ That's possible, I would need to check a unit to be sure.

I looked at the diagram and found another which was slightly different.
One way it could work is for the rheostat wiper and bottom end of the track to be fed a bias voltage, with the other end of the track at Gnd. As the wiper tracks down the rheostat it is dragged more and more to Gnd, which is reflected in the gauge reading.

The version for the trip computer appears to have a separate feed for the bias voltage and the wiper reports to the gauge only.
The other diagram I found had a resistor built into this extra feed, which I suspect is a current limiter. Have a check of both units with a Dmm and all should be revealed.
You could probably de-solder the additional wire and move it to the replacement unit, complete with resistor (if fitted) and connector terminal.

At lest we now know that fuel gauge on maximum and flashing low level lamp, mean the fuel sender is disconnected.

The 4 pin level senders have the 5 wires in them the same as the 5 pin sender, except the black is joined to the brown on the 4 pin and on the 5 pin its separate...

When I refer to 4 and 5 pin I mean the plug on the top of the sender..

Yes, you can see that in the diagram.
2 pins for the pump, then either two, or three for the sender, depending on whether it is for a version with, or without trip computer.
The difference appears to be that one end of the rheostat is connected to the additionally used pin, or to the same pin that the wiper is connected to.

On your diagram, it looks like the rheostat tracks connect to pins 1 and 2, then the wiper connects to pin 1 of the 2 pin unit and Pin 4 of the three pin unit.

The pain is the top plug is obviously sealed so I'm not sure how id get the wire separate and fed through.. I'm cross I broke the proper one as it ended up being completely unnesseary .. it is what happens with my current state as I dont think straight..

Could you drill the top of the unit and then seal it with epoxy once the wire is through?