Positive Boost deviation...No boost leaks, good dv's, wastegates tested, 2 mafs, 2n75

[Dorny1]

So as title states I have the dreaded soft limp, car is stage 3- VAST with intake, full exhaust, 2.0tsi coils, I've swapped the n75 and MAF with another one I know was good. Boost leak tested with no leaks, checked wastegate operation and they kick over quick, plus checked the DV's. Vagcom only shoots up a pos deviation code. I'm totally lost now, i've gone through everything that could be causing it. We also reset the battery and it stayed in boost for awhile longer then as I thought it was good it kicked down and does it almost immediately. Checked again and everything is all good still....What else could cause this code?

[Leflerej]

Do you have larger downpipes or just gutted cats?

[Audimilo]

bad MAP sensor? note- MAP not MAF.

[bmoreS4]

I had the same issue, drove me nuts for months.

It turned out to be the waste gates.

Your over boosting and hitting limp.

[Dorny1]

boost gauge reads what i normally have but i'll swap the map and see if that does it

[zillarob]

I think zee germans do it funny and pos dev is a boost leak, bad check valve, or otherwise having a hard time meeting requested.

[QuinnsterKID]

Im having the same exact issues right now. Pressure tested and I have no leaks. Brand new 710N's and N75. Im going to check my wastegates tomorrow and see what that shows me. What my car does is it goes into limp when I do WOT from lower RPM's. If I am in 3rd or 4th with a higher RPM, say 3000-3500 and punch it, the car makes boost just fine and holds it. How did you check the wastegates? Unplug the N75? Were in the same boat.

[Corradovolksb]

Try logging MVBs 115,116 and 117 with VCDS. That will let you know what your exact overboost and your wastegate duty cycle. If you have ME7L you can use that also and throw the csv in to ecuxplot to see the graphs.


2000 Nogaro S4 stage 2 K&N intake SSAC turbo back exhaust EVOMS DV's SB stage3 daily clutch 42lb injectors V8 FSI fuel pump. 91 and E85 personally tuned.

[Dorny1]

hit the wastegate line going to the n75 with a short regulated hit from a compressor both of them jumped and returned quickly. I'll try the logs, going to flop out the MAP on thursday to see if that does it (helps to know people with lots of spare parts)

[zillarob]

Test the green checkvalve by the #1 injector, the pcv check valve, and maybe the n249.

I think these codes can be goofy and are based on requested psi, not actual psi like we usually think of it.
It may mean the that requested is positively deviating from actual, underboosting.

[LakeTahoeQuattr]

It has been stated that positive deviation p1557 means boost leak. Not too much boost.

I had this issue two weeks ago and it was from fuel rail loose and leak from injector seat. Just my .02

[megafreakindeth]

Positive deviation is caused by overboost. Negative deviation is a leak or some such thing. You just need to check the lines going to the wastegates. There is a three way connector that gets hot and breaks all the time. This will cause the waste gates to not open, thus overboost.
N75 valves get stuck sometimes, and wastegate diaphragms can leak but it's usually the vacuum line to the wastegates.

[LakeTahoeQuattr]

Taken from here:

"Alternately, if your requested boost is far too high for a given load/rpm point, you may experience positive deviation (underboost) limp mode. This occurs if actual boost is too far under requested boost for too long. The result will be the P1557 Positive Deviation code, and from then on out, WGDC restricted to 10%. Note that VCDS reports P1557 incorrectly as an overboost condition, when in reality, it can only be generated by an underboost condition. An actual overboost condition will likely cause P1555, not P1557! Also note that in some non-S4 files (e.g. Golf Jetta LP file), it may also be (incorrectly) reported as P0234 overboost."




Every time I have had a positive deviation p1557 code it has been a boost leak.

[bmoreS4]

Positive deviation is caused by overboost. Negative deviation is a leak or some such thing. You just need to check the lines going to the wastegates. There is a three way connector that gets hot and breaks all the time. This will cause the waste gates to not open, thus overboost.
N75 valves get stuck sometimes, and wastegate diaphragms can leak but it's usually the vacuum line to the wastegates.

This, its overboost.

[Dorny1]

As stated in the original post, the whole system has been pressure checked with NO LEAKS, Wastegates were checked to be opening correctly and not leaking, N75 was replaced with a known good, its either the MAP or checkvalve.

[LakeTahoeQuattr]

clear the code, do a me7 log and send it to your tuner

[airjawed]

Positive deviation is "overboost". Actual is higher than requested. It can be caused by a leak in the wastegate lines.... which is a boost leak in a sense.

[bobkatkat]

Positive deviation is "overboost". Actual is higher than requested. It can be caused by a leak in the wastegate lines.... which is a boost leak in a sense.

Not as cut and dry like Rob/Zillarob stated above. I had an intermittent Positive deviation code when i was chasing down a slow boosting issue where the car would go into soft limp because actual was not hitting requested. It was bombed out Metal cats that were blocking the exhaust.

[zillarob]

As stated in the original post, the whole system has been pressure checked with NO LEAKS, Wastegates were checked to be opening correctly and not leaking, N75 was replaced with a known good, its either the MAP or checkvalve.

A normal psi test pressurizes both the high and low psi sides of the intake and will not show if a bad check valve is leaking between the 2.

[Dorny1]

Well thursday has come and i'll be checking the check valves and swapping MAP sensors to see if that does it. I've checked wastgate lines to and from the n75, and I wish I could send the logs to my tuner but they were shut down (VAST). Really need to get injectors and get a tune...Intake tube/MAF is sitting in my man cave waiting for the day. Codes are cleared out after each test same code every time and i know its not my cats being plugged up...

[Dorny1]

SOLVED!

after really driving the car and having a buddy rolling behind me he smelled brakes...seems the back calipers were locking up. It has been stored for almost 2 months while we worked. we were able to back them off and its been boosting quite nicely.

So after trying to get it to kick the code all day its rolling great...thought something didnt feel right. Calipers will be getting replaced or rebuilt here soon.

[LakeTahoeQuattr]

What?!?! Thats a new one for me. Can you explain how this causes such a code. I am just confused.

[zillarob]

Not going to say it wasnt the brakes, but very doubtful.

If it sat for a bit, my guess is it was just a little cranky and took some driving to get something to free up.

[Dorny1]

Well as I see it, I noticeably felt it release and suddenly it wasnt kicking into limp mode or throwing codes. I figure the drag on the drivetrain caused the load to be way more on the onset of rolling into boost and that caused it to load up. Basically it was brake boosting and getting boost lower in the rpm's than expected.