Diagnostic tests are saying that I've got high pressure in my braking system. I've got a couple of questions and wondered if anyone could help.

Does this necessarily mean the brake control valve/compensator is at fault or could it be something else?

Would high pressure in the braking system make a difference to the suspension? Two indies - Paul Johnson of the former XM Centre and Stewart Agar of Brodie Engineering - reckon it's fine but I know it's not as wafty as my last XM. More BMW than Citroen, in fact.

Any thoughts?

Jamieb

Yep, As Techmanagain said..

Sticky brake valve pivot normally shows up as a dragging brake on the front drivers side wheel - if that's any help. Try jacking up the front and seeing which wheel spins easiest?

Where was the pressure reading taken / measured?

I believe a higher system pressure would tend to make an otherwise good suspension system more floaty rather than less. There's acres on here regarding hard suspension diagnosis - suspension ECU diodes are #1 suspects

thanks for the replies. I've gone through a lot of the forum's hard suspension diagnosis advice (though I've not got involved with diodes as they are outside my pathetically small comfort zone) but when the brake pressure reading came up, I just wondered if that might be part of/the problem, considering it's slight. The reading was taken a couple of weeks ago.

I'll follow advice re brake testing and keep you posted. Then I'll try the diode thing.

Ta everyone

JAmieb

Hi Jamie,

When you say "diagnostic checks" what exactly do you mean? Do you mean plugging it into a Citroen computer in a garage or do you mean temporarily introducing a pressure gauge into the pipework?

I think the answer to this will lie in the nature of the test.

Cheers

noz

Hi Noz

The diagnostic checks were done on a computer so presumably anmy other faults would have shown up. Ah - does that mean a faulty diode would have registered? because as far as I know, the high pressure was the only problem that came up.

thanks

Jamieb

Sorry guys - but how is the pressure reading taken by the computer - I didn't know we had a pressure transducer in the system?

There is a brake pressure sensor input for the hydractive ECU, but I thought that was just a on/off switch?

The report from the garage might be just that the brake sensor is on all the time and forcing your suspension into hard mode?

I don't think that overly high system pressure will affect the suspension. The height correctors work only on body position and once they've closed, the fluid trapped in the suspension cylinders will be sufficient to support the car's weight and no more.

The suggestion put forward previously, that low pressure would result in hard suspension, was based on the premise that if there was insufficient pressure to open the hydractive isolation valve (hope that's the right term), the suspension would remain in hard mode irrespective of the electrovalve position. That makes sense to me, but once the coupling valve has opened, a higher pressure can't close it again.

Derek

Hi Wirdy et al,

That was my feeling too hence the reason for asking about the test. I'm not overly au fait with all of the parameters available through the diagnostic interface but I don't remember seeing anything about high pressure. There's no transducer that I know of, only the system pressure switch.

Jamie,
Did you actually see the computer connected and the result shown or did you take someon else's word for it?

Cheers

noz

I didn't see the read-out but it was an Xm specialist - Paul Johnson of the former XM Centre. I know he said he had run diagnostic tests on the computer because he referred to the print-out and I think he also said that however many times he ran it, the high pressure reading kept on coming up. Sounds like a I should get back in touch with him to see if he remembers.

Thanks everyome

JamieB