So the other day, was driving the trust cayenne home from work and got yet another fun fault message
which never sounds like a good thing in a old 2 tonne 4WD. Plus of course warning lights for empty windscreen washer and an airbag fault - things which I'll fix later on.
Code reader shows P1914 (Brake booster pressure sensor) and P1431 (Brake booster system).
One thing about old european cars - whenever there's a problem with them (and there's lots) it's an opportunity to learn something new.
Basically the brake booster system makes it easier to stop this 2 tonne 4WD - reduces the amount of braking force needed by your leg to slow/stop the car. A bit of wiki knowledge later, and know we know the engine vacuum (from intake) magnifies the force when pushing the brake pedal.
Further google-fu shouws this a reasonable common problem - the best link I found was to https://www.renntech.org/topic/31161-brake-booster-faulty/ which had many contributors commenting they had a crack in the vacuum line to the brake booster - so we can understand why we have that error message.
Search for "porsche cayenne brake booster three way pipe" for the most likely culprit - but don't buy any parts until you've confirmed the source of the problem!
To access the brake booster, it's tucked in around the coolant reservoir, windscreen washer filler and torque arm. Remove the plastic covers using a coin to twist open the big plastic locks and remove the single bolt tucked under the windscreen filler cap.
Fortunately, was able to easily identify a big crack in this vacuum line to the brake booster - it was just under the torque arm, behind the air intake box.
Pretty important to fix - with this vacuum leak, it'll cause the brake booster pump to run a lot more than usual, causing it to overheat and fail. I'm sure that'd be an expensive part to replace!
The lower plastic pipe came off easily because of the crack.
Now, we're in lockdown #6 in Victoria, Australia, with no end in sight... the price for a new three-way tube is something like $200 of course. Anyway, I grabbed a bit of 1/2" ID heater hose (always handy to have in any garage) and some spare hose clamps. Pop a little WD40 in the hose, and slide it over the cracked part of the tube, making sure all the cracks are covered by the hose - and attached the other end over the one-way valve (that disc thing with large barb attachment). Snug up the clamps, but not too tight.
Turned on the car, felt around for any vacuum leaks (the first time I put the hose on, it didn't go down far enough to cover the crack). Used the code reader to reset codes, and all is good again!
However, if you read the renntech contributions, there could be more than one crack at any attachements of the three-way hose. There's also other vacuum connections to/from the brake booster, and a vacuum leak at any of them will cause a similar fault message. WOuld recommend replacing the three way hose if more than 1 crack is found - so when the next brake booster error message appears, will do another check and order the part.