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2010 Chevrolet Suburban 5.3L Flex Fuel with P0172 and P0175 Codes - Rich Fuel Trim Diagnosis

Model: 2010 Chev Suburban Fault Code: P0172 Posted: 2016-11-10 10:10

My 2010 Chevrolet Suburban with a 5.3L flex-fuel engine is running smoothly and shows no drivability issues under normal conditions. However, when I clear the OBD2 codes, both P0172 (Fuel Trim Bank 1/2 Too Rich) and P0175 (Fuel Trim Bank 1/2 Too Rich) reappear shortly after. The short-term fuel trim readings are -2%, with long-term values ranging from -25% to -30%. I'm concerned about the significant negative correction indicating a rich condition. No other diagnostic codes or engine performance issues have been observed. I've performed a leak-down test, which showed no problems and ruled out internal cylinder leaks. I also confirmed that there are no aftermarket oiled air filters installed. Any insights into potential causes such as fuel system leaks, injector faults, or sensor inaccuracies? Additionally, could the flex-fuel alcohol sensor or PCM be misreading fuel blend when E85 is not present in the tank?

Related fault codes

P0172P0175

Comments (5)

Anonymous 2016-11-10 13:07

A long-term fuel trim of -25% to -30% is a strong indicator of a rich condition. Please confirm whether this reading applies to Bank 1 or Bank 2, and if it's short-term or long-term. The presence of both P0172 and P0175 suggests possible leaking injectors, fuel regulator issues, or other sources of excess fuel. Are there any P030x misfire codes present? Perform a fuel pressure leak-down test with the engine off (KOEO) to ensure injectors are energized. Inspecting spark plugs may help identify which cylinder is contributing to the issue. A fuel treatment product like Techron or Seafoam might provide temporary improvement but won't resolve root causes. Has there been any recent maintenance work on the vehicle? Avoid aftermarket oiled air filters as they can interfere with sensor readings.

Anonymous 2016-11-10 13:59

Thanks for the clarification — this is a short-term reading of -2% for both banks, and long-term values are around -25% to -30%. I've completed a leak-down test under KOEO conditions (Key On, Engine Off), and results show no significant leaks. No aftermarket oiled air filters have been installed.

Anonymous 2016-11-10 15:54

Drivability is normal — the engine doesn't hesitate or lose power. Are there any additional diagnostic codes or symptoms? A long-term fuel trim of -25% to -30% indicates a significant rich condition, which may point to an injector leak or sensor error. What are the oxygen sensor readings under various load conditions? Did you perform the leak-down test with the engine energized (KOEO)? This ensures injectors are active during testing. Also, what is your current fuel pressure reading? These details will help narrow down whether the issue stems from fuel delivery or sensor feedback.

Anonymous 2016-11-10 18:28

Note that there was a known over-fueling issue in certain 5.3L Flex Fuel models where the alcohol sensor or PCM misreads fuel blend, especially when E85 is not present in the tank — this can cause incorrect fuel trim calculations and trigger rich conditions like P0172/P0175.

Anonymous 2016-11-11 08:06

Great point, CJ1. There's a known technical service bulletin (TSB) referenced as PIP4792D related to this issue — I recommend your technician review it. The TSB may address PCM calibration or sensor response in flex-fuel systems when no E85 is present. While I can't attach the document directly, you should be able to search for 'Chevrolet Suburban 5.3L PIP4792D' online. This could explain why the engine interprets fuel mixture incorrectly despite proper tank fill.