FeralComprehension

The high pressure hydraulic system in my C4 works great..... in the morning. In the afternoon, it doesn't shut off and the pump gets hot until I unplug it.

The bomb seems to be working, as it takes 59 (!) pedal depressions with the pump unplugged before the boost is gone and the pedal goes hard. This same evidence would seem to point to the pump operating correctly as well.

I don't believe it's the relay (even though it's the original!) as I unplugged the pressure switch during a run-on event and the pump shut down; had the relay been stuck on the pump would have continued to operate.

Is there any more probable cause than the switch?

John McM

My switch went and gave that issue. If the bomb is working and there is no other pressure leakage then its likely the switch. Not cheap.

Kappi2907

Relay defect

FeralComprehension

Is this wrong?

"I don't believe it's the relay (even though it's the original!) as I unplugged the pressure switch during a run-on event and the pump shut down; had the relay been stuck on the pump would have continued to operate."?

Seems logical electrically, no?

Thanks!

DobermanDad

Do you have warning lights? Have you tested the pressure via the valve on the accumulator to make sure your pressure is correct?

Sounds like your switch is bad to me.

FeralComprehension

Warning is intermittent; I sometimes get the one that means the pump's been running too long. Plus it works right most of the time.

No pressure test; I would build a gauge but I think the test port is $pecial Por$che.

To me the evidence says "Switch!" but that's $300, yow.

John McM

I was lucky. I had a C4 and Turbo 3.6 at the same time. The mechanic switched the switch from the Turbo to the C4 and it solved the problem so I knew it was money well spent.

Goughary

Sounds like the pressure switch.

You could try DC auto and buy a used one. But if it were me, I'd bite the bullet and buy a new switch. If that's not the issue you could always resell it. But I think that's your issue.

DobermanDad

I've always wondered if there's a way to rebuild them.

Rocket Rob

Back in '96, I had a relay get stuck and it burned up the PDAS pump. My mechanic replaced all relays as a precaution plus installed a new pump. Its been good since. Fingers crossed.

FeralComprehension

Yah, I bit the bullet last night and ordered a switch, the o-ring, and some other spendy nonsense from Sunset (two $2.50 plastic washers, ~.7" OD, and a couple $6 rubber hood bumpers) and a relay and deep 36mm socket off Amazon.

Thanks for the input; I'll feedback once the new switch is in place.

fasterlaster

I had the same issue that a replacement switch fixed. One thing I noticed when I replaced the switch is that even after flushing the system, the switch part of the system still had nasty looking brake fluid. To my eyes it didn't appear that flushing did anything for that small section of the system, and may account for failing switches. Also you may have to turn down the socket, since that switch location is real tight. Good luck.

Goughary

I'm pretty sure the part of the process where you have the bleeder open on the accumulator and the pump is running- is when the pump is bled. I know that prior to bleeding my car myself, the shops NEVER bled anything other than the brakes and clutch slave. Which was disappointing to find out and has led to my garage becoming the savior of many a c4...lol...

MikeP.

Which was disappointing to find out and has led to my garage becoming the savior of many a c4...lol...[/QUOTE]


Amen.

FeralComprehension

I realized I never closed this out. Look here.