Citroen XM Forum

Dieselman wrote: Tue Dec 23, 2025 6:45 am You could pull out the fuses, or unplug the Hydractive Ecu to force hard mode to be selected, which would be one test you need to perform anyway as part of the diagnostic process.
You can also disconnect each electrovalve return pipe and observe the flow of fluid...which should be a spurt as the valve changes state. Continuous flow indicates a leakage issue.
If you can't go under the car try disconnecting the return at the reservoir.

I don't have the fuse numbers, or return pipe info, to hand.

Dieselman wrote: Tue Dec 23, 2025 6:45 am You can also disconnect each electrovalve return pipe and observe the flow of fluid...which should be a spurt as the valve changes state. Continuous flow indicates a leakage issue.

Dieselman wrote: Fri Dec 26, 2025 5:10 pm F19 is the Ign supply to the Ecu, F34 is the Batt+ supply.
The Ecu is in the engine bay box, the one with two individual plugs, one black, one white.

TigerHunter wrote: Fri Dec 26, 2025 5:29 pm

Dieselman wrote: Tue Dec 23, 2025 6:45 am You can also disconnect each electrovalve return pipe and observe the flow of fluid...which should be a spurt as the valve changes state. Continuous flow indicates a leakage issue.

Wasn't his an S1 model?
S1 only has one HA valve with no return AFAIK

Dieselman wrote: Wed Dec 31, 2025 6:42 am You need to monitor the return flows to see where leakage is.
If there is no leakage the issue must be that the system is failing to make pressure, which assuming the 12mm relief bolt is tight, would be unusual unless there is an air leak at the pump suction pipe.

Themasteryeti wrote: Wed Dec 31, 2025 4:52 pm && I've never actually tried to see if the bolts tight but I'd be surprised if it isn't as the rear of the car lift normally still
&& I don't think there's an air leak, all pipes are tight on with no movements