17965/P1557/005463 - Charge Pressure Control: Positive Deviation

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KraftwerkTurbo

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2001 Audi S4 manual. Getting P1557 code. Described as positive boost deviation = overboost.
Log shows underboost (actual boost not reaching requested boost).
Is the terminology/wording off?
 
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Jef

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KraftwerkTurbo

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Please confirm wording:
P1557 = positive boost deviation = actual boost higher than desired boost.
P1556 = negative boost deviation = actual boost lower than desired boost.
 
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KraftwerkTurbo

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Hello,

if P1557 code is stored, ECU will limit charge pressure.

So ECU 'cuts' boost. Log then shows actual (cut by ECU) boost lower than desired/requested boost?
I always thought the desired/requested boost is what the ECU WANTS to achieve.

I have had occurrences when the ECU 'overrides' my request for higher boost; but then the log showed this 'overridden' lower boost as the desired boost.

actual boost: pvdkds_w
desired boost: plsol_w
 
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Uwe

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Please confirm wording:
P1557 = positive boost deviation = actual boost higher than desired boost.
P1556 = negative boost deviation = actual boost lower than desired boost.
Unfortunately, this wording has always been a bit vague and confusing because it seems to reference amount of duty cycle the ECU applies to the boost pressure control system. On some engines more duty cycle increases boost, while on others it decreases boost.

-Uwe-
 
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Jack@European_Parts

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Let me see if I can help.

The boost has been cut, because the ECU sees a boost level higher than expected.
Typically one that exceeded 150 MBAR from the request...in either direction sets a DTC.
Hence it stores a code within the DCY, & once the code is present, it will restrict boost by lowering the request to a limp value.

Two things initiate this limp mode being lifted.............Ignition Key/terminal 15 is cycled, or DTC reset by scanner command 0x01-02-05.

Once the key is cycled, the DTC is stored in EEprom, however, not cleared and limp mode is lifted; until of course the boost threshold request table is violated again, with the deviation.
Once the deviation happens to exceed the threshold, you get the limp mode again resulting in boost, timing and fuel cuts.


The DTC is reporting the event .....not what is happening while in limp mode that you are observing, & believing something is a mismatch for the definition.

It is suggested that you clear the DTC and immediately log the issue, to see what the problem actually is, with live data before it makes a limp.

Many things can cause a boost PSI to be to high.........carbon restricted intake in TDI's for example or WG stuck closed FULL ON no boost control.

Boost in Positive is HIGH ( Over Boost )
Boost in Negative is LOW ( Under Boost )
 
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KraftwerkTurbo

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KraftwerkTurbo

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in photo/link below:

Red curve = desired boost
Blue curve = actual boost

Code:
17965 - Charge Pressure Control
P1557 - 35-10 - Positive Deviation - Intermittent


https://drive.google.com/file/d/0B1Tf8CeTSTXbS2hEMWE5WDVpbTA/view?usp=sharing

Here is another log with lower desire boost. Actual clearly lower than desired boost. Yet code says 'positive deviation' (in my words: overboost).
https://drive.google.com/open?id=0B1Tf8CeTSTXbc1RsY1prTDdZUG8

Note: this car does not have a boost gauge (hate it). Would take the guesswork out of interpreting the error code language. Anyone know what the Bosch/Audi original language (German) is for code 17965? Maybe something got 'lost in translation'?
 
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KraftwerkTurbo

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Found this post/line on Audizine: "It may mean the that requested is positively deviating from actual, underboosting."
Same post, other poster: "It has been stated that positive deviation p1557 means boost leak. Not too much boost"

So 'reverse' logic at work here?
 
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Jack@European_Parts

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Found this post/line on Audizine: "It may mean the that requested is positively deviating from actual, underboosting."
Same post, other poster: "It has been stated that positive deviation p1557 means boost leak. Not too much boost"

So 'reverse' logic at work here?

You are ass backward..........:p

See post # 7
 
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KraftwerkTurbo

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You are ass backward..........:p

See post # 7

That is what I think. Overboost is actual higher than requested. But having 'overboost' code and all logs showing actual LOWER than requested does not make sense.

I will smoke (leak test) and find out if boost leak (underboost) or N75/wastegate/compressor line leak (overboost), and disregard the confusing (english translation?) terminology for now.
 
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