Checking Pilot Pressure Valve

General

Normally the pilot pressure valve is checked within the scope of measuring the friction coefficient of the transverse lock (test item 3).





A pilot pressure valve (arrow) is located ahead of the transverse lock slave cylinder on the left-hand transmission side.

If pilot pressure is too high, squeal noises may result. Due to wear and vehicle dynamics constraints, zero pilot pressure is also to be avoided. When replacing components, do not confuse with the PDAS pilot pressure valves designated for the 911 Carrera 4.

Specifications / identification of the pilot pressure valves





1. Prepare vehicle for pilot pressure valve check.





- Connect ring flange (No. 3) to measuring line (No. 2). Proceed by fitting this assembly complete with banjo bolt, seals and fitting (Nos. 4, 5 and 6), to the lock cylinder, replacing the bleeding valve. Connect high-pressure measuring line (No. 2) to pressure gauge.

Important note: Tighten Nos. 4 and 6 carefully and lock when tightening, making sure the parts do not bind. It this is not observed, the fitting (No. 6) may shear off.

- Connect System Tester 9288 along with adapter line 9288/1 to diagnosis socket (located next to the passenger's seat under the booster cover).

- Bleed pressure gauge by clocking lock solenoid valve complete with System Tester in "Drive links / Bleed position" menu and allow brake fluid to escape from the pressure gauge at the bleeder valve until it is free from air bubbles. (Use collector bottle). For this purpose, leave bleeding device connected to reservoir and leave bleeding line clamped. Bleeding pressure approx. 1.5 - 2.0 bar.

- Close bleeding valve and press stop button. Select pressure reduction position.

- Switch off bleeding device.

2. Check pilot pressure valve operation as described below:

- Use System Tester 9288 to activate transverse lock solenoid (Drive links / Check transv. lock menu) with 1 - 2 pulses.

- Then switch to pressure reduction position and read off gauge pressure after a short interval (to allow for gauge damping).

- Refer to image for pressure specs.

Important note

If pilot pressure is too high (before replacing a valve), build up a lower pressure and reduce pressure by switching off the ignition, thus deviating from the previous testing procedure.

Pilot pressure may drop by max. 0.2 bar within 5 minutes.

3. Follow check by bleeding the transverse lock and correcting the reservoir level.

- After disconnecting the pressure gauge, use the System Tester (Drive links - Select bleeding menu) and allow brake fluid to escape at bleeder valve of the transverse lock slave cylinder until fluid is free from air bubbles.

- Correct reservoir level with accumulator fully charged (after pump unit has switched off automatically). Do not fill above "max. mark". Screw on reservoir lid. Open venting line at reservoir again. Disconnect System Tester.