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Diagnostics issue, long term negative fuel trims.

Gatley

New Member
Joined
Nov 27, 2019
Messages
4
Location
Shropshire UK
Car
GL500
I have a 2012 year Mercedes GL500 with engine codes P0172 and P0175 (Mixtures bank 1 and bank 2 rich) . Long term fuel trims are circa negative 25% Short term trims around negative 3% Car drives, runs and idles normally but fuel consumption seems high even for this small truck
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O2 sensor readings seem OK but I am no expert. Both front and aft sensors are wideband. I intend to remove the MAF sensor and see i I can see deposits, assuming it's a hot wire type, but a physical examination shows the air filter assembly is not secured properly on the MAF assembly, the clips are not fastened correctly. Could this be enough to influence the long term trims? A full throttle blip shows a rapid change in MAF voltage up to a high level. Plugs and air filters are new, fuel filter was changed less than 6000 iles ago.Vehicle is under 40,000 miles total, any guidance as to what to check appreciated. Scanner is Bosch KTS. Thanks! BTW I have been unable to delete these codes with the KTS, I am not sure why... I am new to the KTS and scan tools in general.
 

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