P0175

A closed loop air/fuel metering system is used to provide the best combination of driveability, fuel economy, and emission control. In this system, short term fuel control is accomplished by the ECM rapidly responding to the oxygen sensor readings. These changes finely tune engine fueling the long term fuel trim control is determined by the trends of the short term fuel trim. The ECM uses the long term fuel trim to make course adjustments to the engine fueling. Under normal driving conditions, except power enrichment mode and extended decelerations, the ECM attempts to maintain a 14.7 to 1 air/fuel ratio. Fuel trim values of 0% are ideal. If the value is above 0%, this indicates the engine is running lean. Therefore the ECM commands more fuel to the system in attempt to maintain a 14.7 to 1 air/fuel ratio. If the value is below 0%, this indicates the engine is running rich. Therefore the ECM commands less fuel to the system in attempt to maintain a 14.7 to 1 air/fuel ratio. The ECM stores many different fuel trim values for two ranges: idle/decel and cruise/accel. The idle/decel range is known as the additive fuel adaptation range for which only a small amount of fuel is to be added or removed due to very low engine loads. The cruise/accel range is known as the multiplicative adaptation fuel range for which a multiplying factor of fuel is added or removed due to higher engine loads. DTC P0175 will set if the long term fuel trim value for bank 2 (cylinders 2, 4, 6 which are closest to the radiator) in the idle/decel or cruise/accel ranges exceed a lean calibrated threshold. This indicates the fuel control system has to remove too much fuel (bank 2 is running rich) in order to maintain a 14.7 to 1 air/fuel ratio.

DTC PARAMETERS
DTC P0175 will set if the vehicle is in closed loop and either of the following long fuel trim values for bank 2 have been exceeded (more negative):

Idle/Decel: -8.1%

OR

Cruise/Accel: -23%

^ Bank 2 loop status is closed
^ No MAF of HO2S bank 2 sensor 1 DTCs have been set

DTC P0175 diagnostic runs continuously once the above conditions have been met.

P0175 is a type B DTC.

DIAGNOSTIC AIDS

IMPORTANT:
^ Diagnose any ECT, fuel injector, IAT, heated oxygen sensor, MAF or TP sensor DTCs first.
^ LTFT BN 2 CRUISE/ACCEL (long term fuel trim bank 1) parameter on Scan tool is only updated under moderate to heavy engine loads. As a result, between off idle and 80 km/h (50 mph) under light throttle, this parameter on Scan tool will not be updated. Use LTFT BN 2 IDLE/DECEL parameter on Scan tool to verify the system is running rich at idle (less than -8.1%) or LTFT BN 2 CRUISE/ACCEL above 50 mph to verify the system is running rich during cruise (less than -23%).
^ If DTC P0172 and P0175 are set, a problem may exist in the MAF sensor circuit or the sensor may be contaminated. If the MAF sensor skews towards a higher voltage, the system will be running rich. Check sensor for signs of contamination (moisture/oil), then compare sensor voltage to a known good vehicle under the same operating conditions.

Other possible causes if DTC P0172 and P0175 are set:
^ Fuel pressure high
^ EVAP purge solenoid stuck open
^ ECT skewed towards a lower temperature
^ MAF sensor signal voltage skewed high

Possible causes if only DTC P0175 is set:
^ HO2S bank 2 sensor 1 contaminated
^ Fuel injectors leaking
^ Restricted exhaust