Audi C5: Allroad boost leak causing overboost??? 

Video showing VCDS "label file editing" to follow next week... sorry about the wait.

That was awesome. Even though the PIDs fooled you you still worked through it. I appreciate the effort you took to explain and diagram it for us. Sweet diagnosis. Thanks!

This is a great video. I am having this exact same problem with my allroad. Gives me some ideas of things to check next.

I can see where having the label PIDs reversed could get you into trouble. Good explanation Thomas of pointing it out along with why the boost pressure is high when there is a leak. Makes sense to me :)

Interesting diagnostic Thomas. Your explanation made sense to me.

Makes sense. The boost is leaking so it's not giving the engine what it wants or what sees so it tries to give it more and that hole is not a constant so sometimes the boost is too much. Real good color schematic. Nice. Good video Pal. Happy New Year.

Good stuff BTW. I Have to watch more of this stuff.

I'm having the same issue my self on my 05 2.7 allroad. I just tested my n75 and wastegate lines. They were fine. My tune is for 18psi, but I'm surging upto 25psi in wot. I'm about to smoke test my engine on 15psi to see if I can find any leaks.

Makes sense great analysis

Good work

Thank u sir

I was under the impression the boost pressure readings you see in VCDS were from the MAP sensor in that boot, and the pressure lines that go to the N75 to power the wastegates were the ones connected to the compressor housings of the turbos. If that's the case, the wastegates would get decent stable pressure that would always be more than what the MAP sensor sees. I'm interested in your thoughts.

Great video Thomas!

every throttle body boot tears in that place causing that over boost its make up air added and the n75 cant calculate it

This is very interesting, did you have an over boost code? It seems like it was under boost then after the fix values were good. Maf-map readings would help in this case right?

a question I have to change head gaskets and valves for that I have to remove the springs or the valves come out without removing the springs my car is Audi 1999 a6 quattro 2.8

Your workbench with all the pits in it is freaking me out. In 2018 im wishing that top is replaced . How many time did you miss and hit that work top - wow :)

Electrical tape will fix that right up. I think your explanation makes sense 🤓

Interesting! Always annoying when you have trust issues with scan tool data... Doesn't the N75 take boost pressure right after the turbo's? Up there the boost should be good. I dont know the twin turbo setup from audi that well. Otherwise your explanation sounds very logical. Best wishes Thomas

I have an MK4 1.8t Golf that is getting this code and goes into limp mode. Boost leak tested, smoke tested, new N75E (N75J previously), new MAP, new MAF, new diverter valve, new turbo/wastegate, all factory hoses replaced and still limp mode and P1557. The car has a mail order tune from GIAC. I searched online and found some individuals with GIAC tune who had this problem due to the tune, but I called GIAC and I was told that it is definitely the N75J valve that is causing the problem. I replaced it with the recommended N75 and the problem continues. Is there anyway to verify that the tune is/is not the problem? I've taken it to a VW specialist with VAGCOM, but he could not figure out what caused the positive deviation code. Any direction would be appreciated.

I guess the leak required more turbo boost...for a given rpm, vehicle speed, load, etc the pcm didn’t see what it is mapped to see. Therefore an overboost condition is present. I think 🤔 😂

hahaha thats every tbs on all 2.7t audi normal tear is lower section over boost reading but no real boost

Your brain hurts?, mine is overboosting lol :-D. I know nothing about this system, but when feedbacks dont agree with reality and the leak is a bit random, im not supprised the computer made the wrong adjustment, and made things worse. I did say i know nothing lol.