A few months ago I sprung a leak at my pressure differential regulator, that little plastic valve that screws into the union fitting near the driver's side wheel well, that expensive (for a little piece of plastic) part that also - I think - functions as the brake failure light sensor. I replaced it, bled the system, changed the master cylinder for good measure (almost 200K on the original), and off I went. It just started to leak again, still a fairly slow leak that I have to top off every other day or so, but I'm wondering if there's something else going on that might be causing this leak to be recurring?

I had the same problem and replaced the entire unit, replacing the switch will not cure the leaking. The leak originates inside due to worn piston seals. The switch body is not intended to seal against and withstand the internal pressure. The job is a bit awkward getting in there to disconnect all the lines, did it from underneath. I disconnected or loosened the all the lines I could then removed the single mounting screw for the rest. Fill the reservoir with fluid then seal the small hole in the reservoir plastic cap with a piece of tape to minimize dripping while you work. Of course bleed when done.


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David Hunter

I also had the same problem. All I had to do was to re-tighten the switch.

Kyle245

I had the same problem. Replaced the switch, still ok after twelve years.

But then...your mileage may differ.

Doug Harvey

Just remembered...

About four years after replacing the switch, a shop sold me and installed a rear axle. While they were in there, they put in IPD brake lines AND installed the brake system pressure-balancing box that the switch screws into (Volvo only sold the whole thing as a package).

So the new switch rode ok with the old box for maybe 80k.

That's all I know about this issue.

Doug Harvey