2010 XC60 T6 Short Term Fuel Trim +40% Topic is solved

[Rich054]

Hi all, I´m dealing with an issue with my short term fuel trim (STFT) and therefore fuel economy also. The STFT switches to +40% and stays there until I ´´reset´´ it by driving without throttle for 5 or more seconds.

Conditions that trigger +40% STFT:
- Highway driving at 75mph or higher. I´m able to recreate this also at 65mph and 4,500rpm,
- hard acceleration.

Things done so far:
- No air leaks (smoke test),
- no misfires when STFT is at +40% (just a 2 or 3 after cold start, I consider this normal),
- premium 93 octane only,
- engine adaptations reset in Vida - helped with delaying the onset but it´s still there,
- cleaned MAP and MAF sensors,
- LTFT is at 2% as long as I don´t let the STFT stay high,
- downstream O2 sensor was replaced, upstream one looks to be working properly,
- replaced spark plugs - no signs of engine oil, etc. they looked ok,
- VVT solenoid cleaned and tested.

I have 2 DTCs in CarScanner App, which my Vida2014 does not read:
P0170(68) - Fuel trim, bank 1 - malfunction
P1170(68) - ESO - Engine Shut Off Solenoid Fault
Does the T6 engine even have shut off solenoid?

O2 sensors also sense richer mixture and STFT stays high, which is not making any sense to me. Shouldn´t they be trying to balance themself? Like when O2 sensor sees rich fuel mixure, the STFT should be trying to reduce fuel therefore be in negative numbers?

Any suggestions are welcome.

[Rich054]

I ended up replacing the VVT solenoid and also fuel pressure sensor without any change.
New observation: STFT switches to +40% everytime i go up any steeper hill.

[Rich054]

Replaced upstream o2 sensor from top - removed PCV cover. Problem is gone.