vandal968

I'm slowly working through my new-to-me TurboPig's glitches. I've got the "Brake Booster Failure" warning and I've been removing panels and digging around looking for a leak. I just discovered that the silver vacuum pump on the passenger side had its cable unplugged, so I plugged it in. I have not noticed any change, I still have the warning and the brakes still feel the same (fine). The connector doesn't seem prone to unplugging itself and the seller said that he had already ordered a replacement part although he said "tube" not "pump". Is there a procedure to test this thing? Is the booster error something that will clear itself once resolved, or do you need to clear a code? Also, I had assumed that those two big black things at the rear of the engine over the valve covers were vacuum pumps, clearly they're something else. What are they?

cheers,
c

AGARubberDuck

It's pretty typical for the vacuum line to split on the right-side of the engine compartment (left, if standing in front of it).
You found the vacuum pump, but for many of us the line is actually split and allowing leakage further down. Check out the 5th or 6th post for pictures here:
https://www.renntech.org/forums/topi...comment-224473
For my 04, I could hear the vacuum pump clearly still running and trying to keep up with that massive leak. The pump would actually get quite hot to the touch. I'd imagine if left too long in this state the pump will burn out.

Those two large black pumps are secondary air pumps, basically to pump extra air through when warming up to comply with emissions.

Edit: the error comes and goes depending on whether the system thinks enough vacuum is present. Mine would show up on startup on cold mornings and stay on until the next key cycle. If the engine compartment was warm the error would typically stay away after startup. If the seller said he ordered a 'tube' I'd be looking below the torque arm for a split in the vacuum line. Parts of that line are hard plastic.

vandal968

So is the pump supposed to always be on, or does it cycle depending on whether or not the engine is pulling vacuum?

I should be able to just give it 12v and hear it spinning if it's good, right?

c

AGARubberDuck

The pump cycles as needed. If it was unplugged, it may have been done to save it from running all the time.
I'm not going to recommend hooking up 12v directly to it, but with it plugged in you should be able to hear it for 15-20 seconds on startup.

Oh, and don't put your finger over the vacuum hole. It'll give you one hell of a hickey if it's working right.

vandal968

I put a meter on the harness that goes to the pump with ignition on but engine off, I was getting small values (mv) that jumped around a lot. Not 12v continuously as I'd expect. Maybe it sends small voltages first to test the pump or something? Don't know. I tried connecting the pump itself to a 12v wall wart and it spins, so it doesn't appear to be broken. With the pump plugged back into the harness, I drove around the block. The car feel exactly the same as it did with the pump disconnected, so I don't think that it's doing anything. Brakes feel fine, heavier than my 968, but I wouldn't consider them "broken" if it weren't for the warning light.

I'll keep poking around, but all of the plumbing looks like it's in good shape. I wonder why the pump was unplugged.

c

vandal968

AGARubberDuck,
I disconnected the pump, cleaned the terminals and plugged it back in. Now, when starting, it runs for 10 seconds or so, then cycles off. I waited for 30secs and it didn't turn on again, so I don't think I've got any big leaks. Then I went for a drive, the brakes feel stronger, it's not a huge difference, but I think the pump does make a small difference (probably matters a lot more at speed). The warning light is still on. I did notice that now with the pump connected, when I tap the brakes with car stopped, engine running, I hear something that sounds like a plastic door slamming behind the dash. Never heard that before with pump disconnected. Any idea what that might be?

cheers,
c

vandal968

Just ran down the the local P-car dealer to get some stuff. The brakes are noticeably improved at speed. I wonder why the heck the pump was disconnected. Oh well, going to reinstall all the panels and call it good. Thanks for the help.

cheers,
c

reachme

Why is it I always read warnings AFTER I do something. It didnt give me a hickey-it sucked a few layers of skin clear off my thumb and took a chunk out of it.

BTW I did find my second leak. . .at the T connection underneath the brake booster pump. I'm just going to replace the whole thing

Dilberto

https://www.renntech.org/forums/topi...ooster-faulty/

nodoors

I had intermittent errors for a while. The original pump seemed to work fine, but after replaced it with a part out of an Audi I have not had an error in over a year.

So although it may not be common, there is a possibility it could actually be a fault with the pump and not a leak.

vandal968

Seems to be working great, but I still have the error(service required). People have said that it self-clears after a while but I wonder if since the pump was physically disconnected rather than just low-vacuum,if it tripped something that needs to be reset via OBD. Trying to figure out which reader to purchase. Deciding between the Por-II or the X431. I've got the 04 Cayenne Turbo and an 06 Infiniti M45. It would be nice to be able to read/reset things on both. I've also got a 93 968 which is pre-OBD.

cheers,
c

deilenberger

iCarScan (google it) will do all of your vehicles.

ProgRockJunkie

Mine recently died. Replaced at $218.30 from this guy. All better. Assume the guy who knew the corresponding Audi part paid less.

http://www.ebay.com/itm/Porsche-Caye...72.m2749.l2649

v10rick

Automotive pumps are often speed controlled by the engine CPU using PWM (pulse width modulation). Most digital voltmeters will read this but don't expect to measure 12V all of the time. The voltage will fluctuate while it regulates the pressure.

A better test is measure the vacuum the pump generates. A vacuum gauge can be had for under $10.

A diagnostic scanner like the Durametric will flag an error if the vacuum is too low.

2008 and up Cayenne's changed to an engine driven pump. The vacuum measured 20" with a new pump.

vandal968

My new-to-me 2004 cayenne turbo had the "brake booster failure" message. I dug around for vacuum leaks and didn't find any. I DID discover that the vacuum pump had its connector disconnected. I reconnected it, brakes improved, the pump would cycle for 10 seconds or so on start, then remain off as others have said it should, which seems to confirm no vacuum leaks.

I ordered the iCarScan and received it yesterday. I was able to clear the brake booster fault, but made the mistake of running my battery down while doing it. The battery dying led to a series of new faults such as air-suspension PSM and steering angle sensor. I hooked up a 10/55a charger and tried again on the 10a setting, but it runs the battery down too fast. On the 55a setting, I only get a few minutes before the thermal relay in the charger trips and it goes off for a minute or so to cool, then cycles back on over and over. Even when cycling it gives sufficient power so as not to let the Cayenne run low, but the on/off surge was enough to give me an error for the electronic compass sensor (something like bus 30 too high, which I assume is the main DC rail). Anyway, after a lot of screwing around I finally got all faults to go off and stay off, even the mysterious trailer hitch error that was there initially (before the low batt fiasco). Just now I drove to Target to pick something up, and on the way back, the "Brake booster failure" came back. I don't seem to have a vac leak, since the pump cyles on engine start, then stays off, so my best guess is that the pump itself is failing, either too little vacuum, or maybe it intermittantly gets stuck, perhaps that's why a previous owner disconnected it initially?

Should I buy the pump, or do I still need to do more testing?

Also, I'm going to buy a proper 40A charger per the manual, none of this 10/55 engine start stuff. Anyone have a recommendation for a good 40A continuous charger?

cheers,
c