NefMoto

17964 - P1556  Charge pressure control; negative deviation. HELP please

With zero relevant info...

overboost.

https://s4wiki.com/wiki/Tuning#Negative_deviation_(overboost) (https://s4wiki.com/wiki/Tuning#Negative_deviation_(overboost))

i had this issue about week now with no fault codes stored on ecu and my boost guage won't pass 5 psi with no check light on,a friend of mine told me to get hard on my s4 get it under load its will throw codes i take my s4 for spin on highway i hit the gas on 3th gear full throttle suddenly check engine turned on when get to my home pluged in vagcom scanned for cods i found this code 17964 - P1556  Charge pressure control; negative deviation

n75, wg lines, wg.

so this code means over boosting or under boost if over boosting this drive me to start checking  boost control starting from  n75 to wastegates 

overboost -> limp -> limited to 5psi

Good news i fixed it
now my s4 hits 20psi again 
The check valve that connected between the intake manifold and evap valve was connected backwards

Everyone loves some boost in their fuel tank.

I'm trying to figure out how this led to neg deviation though

If it was 10 years ago when I had the 2.7T hoses memorized in my head, I'd tell ya.

;D ;D that's me, now i know why i smell gas on my s4 capin

P1556 is LDRA.

lde > EDLDRP and lditv_w >= TVLDMX for TDLDRA

Yep, that's overboost... but why did the checkvalve error produce overboost?

Actual boost is at least EDLDRP less than target


Max DC is unable to correct the error

that sounds like positive deviation

http://nefariousmotorsports.com/forum/index.php/topic,871.0title,.html

neg deviation limit should be lde very negative and ldi reaching minimum due to overboost.

I've seen this swapped, depending on scan tool and even ECU

http://nefariousmotorsports.com/forum/index.php?topic=7524.msg69342#msg69342
http://nefariousmotorsports.com/forum/index.php?topic=7524.msg69436#msg69436

I don’t know about the semantics of the description, but in 551M:

LDRA throws P1556 (underboost)
LDO throws P1555 (overboost)

LDRA will also throw P1556 if the ratio ps_w/pvdkds_w exceeds the threshold from KFVPDKLD.

Positive deviation is always underboost and negative deviation is overboost.
Too lazy to check but scan tools get them wrong sometimes.

i see you all guys are still confused about my situation here
here is the story my car is 2002 s4 2.7t tiptronic swapped to manual transmission a year ago, the original ecu  was aa-box flashed to m-box, i did some modes on that car like rear os delete egt delete and rebuild  both turbos.
since then car runs just fine no issues at all no chek lights , but about a week  i start smelling gas i poped the hood i found all injectrs leaking gas evry where i tought its maybe the injectors seals needs to be replaced and i did replaced all injectors seals and when i did that i think i installed back the check valve for the evap valve  backwards because since then the 5psi issue start to happen with no fault codes because i never get my s4 under load or hard driving so maybe  that's why she is not throwing fault codes
i took my friend advice pushed my s4 hard on highway till the check light turned on returned back to my place plugged in vagcome and found the P1556  Charge pressure control; negative deviation
i fx it now every think good but my injectors still leaking
replaced the fuel rail same thing all injectors leaking so i thoaght its mybe the injectors are bad.
 i got 06a9060311.8t injectors in my garage so i told to my self lets try them so i puted  them on ,car start fine no leaking gas any more so i orderd ev14 550c injectors and that's it end oof the story

Have you checked wastegate cracking pressure with a gauge and hand regulator before installing rebuilt turbos? Could have boost creep due to wastegates not being set correctly Also, make sure the n75 is plumbed proper and hoses are not burnt / melted going to the wastegate actuator. Posting some actual logs would really help your situation. 

no i didn't check the wastegate with gauge but i did test them with compressed air they are working properly and about  the n75 valve i clean it with wd40, installed back checked all pressur hoses from the n75 to wastegate all good i will do some logs but what's about the leaky injectors are thy failing like that leaking like the are cracked