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My 05 CTT developed a brake booster faulty code and I cant seem to get it to go away. We have redone all vacuum hoses (many vacuum leaks), replaced the melted vacuum pump. The code comes right back after pumping the pedal a few times because although the ECU has the right values to fire the vacuum pump it isnt pumping. Any thoughts on why this could be? I've heard the boosters have a sensor in them that goes bad and cant be replaced - would this prevent the vacuum pump from firing?
Likely your brake booster hose behind the cowling is shot. Not a fun DIY either.
What if I said we already redid that vacuum hose (with vacuum line, not the OEM hose) and the problem still exists? Could it be something related to not having the OEM hose? EDIT- Also the sensor reads an accurate reading in the ECU and the booster holds vacuum... So on the physical side of things all is well. The vacuum pump was replaced as the old one was toast because it must have been running all the time. The new one just doesnt fire and when it doesnt it throws the code.
-Will
Last edited by Cayenne955TT; 03-20-2020 at 10:52 AM.
On the TT the vacuum pump acts as a booster for engine manifold vacuum.
It should turn on when the engine vacuum is too low.
How would you test this by replicating actual driving conditions in a parked in a garage?
On the TT the vacuum pump acts as a booster for engine manifold vacuum.
It should turn on when the engine vacuum is too low.
How would you test this by replicating actual driving conditions in a parked in a garage?
I only know two two parts of the system are good - The computer shows that the vacuum sensor in the booster line is reading a nominal value, and that there are no vacuum leaks/the booster "works". Are you telling me the logic is only designed to fire the pump if the engine vacuum is too low, with no reference to the vacuum line sensor reading? Plus, the booster faulty light comes on concurrent with when the vacuum pump should be running. Should the pump be tested in any sort of other way I am missing?
I only know two two parts of the system are good - The computer shows that the vacuum sensor in the booster line is reading a nominal value, and that there are no vacuum leaks/the booster "works". Are you telling me the logic is only designed to fire the pump if the engine vacuum is too low, with no reference to the vacuum line sensor reading? Plus, the booster faulty light comes on concurrent with when the vacuum pump should be running. Should the pump be tested in any sort of other way I am missing?
-Will
Unfortunately there is little documentation on this, it keeps the P dealer service shops in business.
The vacuum circuit is not only for the brake booster, it supplies the EVAP emissions system as well. Since there are check valves in this circuit (#4 in the diagram), no leaks at the booster does not mean the entire vacuum circuit is free of leaks.
Are you certain there are no emissions system errors.
This is the only diagram I could locate for the GEN1 TT
Unfortunately there is little documentation on this, it keeps the P dealer service shops in business.
The vacuum circuit is not only for the brake booster, it supplies the EVAP emissions system as well. Since there are check valves in this circuit (#4 in the diagram), no leaks at the booster does not mean the entire vacuum circuit is free of leaks.
Are you certain there are no emissions system errors.
This is the only diagram I could locate for the GEN1 TT
Interesting - thank you very much for the insight! The car certainly has no CEL, I cant speak to specific emissions codes but I figure the CEL would be set because that involves the emissions?
Would you say that the check valves are the issue or possibly just something in the emissions/evap system in general?
Interesting - thank you very much for the insight! The car certainly has no CEL, I cant speak to specific emissions codes but I figure the CEL would be set because that involves the emissions?
Would you say that the check valves are the issue or possibly just something in the emissions/evap system in general?
-Will
Depending on the size of the leak it may not set a CEL. This is when a scan tool like Durametric would help.
Since the vacuum circuit is like a series circuit its impossible to say exactly whats at fault.
A smoke test could provide a clue.
Depending on the size of the leak it may not set a CEL. This is when a scan tool like Durametric would help.
Since the vacuum circuit is like a series circuit its impossible to say exactly whats at fault.
A smoke test could provide a clue.
10-4 Good to know. I'll loop back with what I find out. I just wasnt sure if there was any known Cayenne issue in the EVAP system that fails, etc
Have you confirmed voltage at the vacuum pump? You can usually trigger the pump by pressing the brakes 5 or 10 times in succession.
If no voltage at the pump connector, have you checked your fuses and or traced the wires to the pump?
Have you applied 12V to the vacuum pump -- does it work on a stand alone basis?
Have you confirmed voltage at the vacuum pump? You can usually trigger the pump by pressing the brakes 5 or 10 times in succession.
If no voltage at the pump connector, have you checked your fuses and or traced the wires to the pump?
Have you applied 12V to the vacuum pump -- does it work on a stand alone basis?
The pump should trigger sitting with the key on engine off? The pump was tested/is new to replace the toast old pump.
I think I usually only hear my vacuum pump when the engine is running. A few hard pumps of the brakes in succession will trigger it.
Great - That is what I thought and that is what isnt happening. Meaning it is either something preventing the pump from running (logically), or an issue in the wiring/ECU/fuses (physically). I'll keep you guys posted. Havent had a chance to work on it, been swamped. Should be soon though, I need to shuffle vehicles around.
Alright - I got the car back and the booster issue still exists. Every single vacuum line in the car was replaced. The engine runs a lot smoother but the booster issue still exists. Interestingly enough - I updated my durametric software and beforehand I could access brake errors/info. The new version doesnt seem to have that option or my car isnt showing the option. Could there be a partial ECU failure? The rest of the car seems to be fine...
What if I said we already redid that vacuum hose (with vacuum line, not the OEM hose) and the problem still exists?
-Will
The line behind the cowl that comes off of the booster, is part specific based on year/vin. It also has a sensor inline (at least my 06 did). How did you compensate for that with generic vacuum hose?
03-19-2020, 08:10 PM
CTT Brake Booster Fault?
