reset brake pressure differential sensor?

[Daveo91Burb]

How do you reset or re-center this guy? It is tripped to one side and my brake light is on. Pretty sure I know why: PO or PO before him broke the bleeder screw in the right caliper, drilled it out, re-tapped with bigger threads and then screwed in a weird sleeve that the bleeder screw goes into. I'm guessing the intention was that the sleeve would stay stationary and the bleeder screw would unscrew as normal, but the opposite happens and it fails to operate as a bleeder (fluid just comes out around the sleeve's threads). It's making bleeding difficult and my messing around with it has caused the sleeve to leak, so when I hit the brakes, there is no pressure at that caliper and it trips the sensor. But all that's a guess so tell me if I've got it wrong! Anyway, will be installing new calipers but want to check if there's a procedure to get that sensor to reset. Or will it be automatic, once all four brakes have pressure? Thanks!

 

[chengny]

The long version of the procedure to reset the P/C valve switch is attached at the bottom. But after everything is buttoned up and bled, try the short version first. It works for me nearly every time.

Short version:

While rolling slowly, SLAM on the brakes. Do this until the warning light goes out. It usually rests on the first try.

Long version:

Note: I gather from what you posted (“ so when I hit the brakes, there is no pressure at that caliper and it trips the sensor.”), you already know that it’s your front hydraulic circuit that is blocked off. You can skip straight to the centering/reset procedure

Identify the blocked off brake circuit:

First you have to determine to which side the valve spool has shifted and whether the it’s the front or rear lines that are blocked off.

1. Set up one front wheel and one rear wheel for bleeding at the same time.

2. Crack both bleeder screws and gently pump the pedal a few times.

3. The blocked side will only trickle fluid out when the bleeder is cracked and the
pedal is pressed. The unblocked line will squirt fluid out the bleeder.


Center the valve and reset the switch:

1. The bleeders on the lines that are clear (the rear lines in your case) must be left open. Manual says to have both open but just one is plenty

2. The blocked lines (front calipers for you) should have the bleeder screws tight to cause pressure to build up on that side. Be sure to use the standard bleeding procedures to prevent air from entering the system.

3. Slowly press the pedal with steady pressure a number of times until the light goes
out; this will center the differential valve.

You may also hear a pop come from the proportioning valve. This is the spool within the metering valve returning to its equalized position. When the light goes out, close the bleeder screw.


Valve internals:

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[Daveo91Burb]

Thanks for both versions! Here's to hoping the short one is the one that works for me!

 

[chengny]

It will.

 

[Daveo91Burb]

Even shorter version: while it was still on jack stands with key in run, engine off, I just hit the brake pedal hard a few times and it went out. Thanks!