DTC P0174: Fuel Trim System Lean - Bank 2: Description

WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

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 percent are ideal. If the value is above 0 percent, 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 percent, 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 P0174 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 calibrated rich threshold. This indicates the fuel control system has to add too much fuel (bank 2 is running lean) in order to maintain a 14.7 to 1 air/fuel ratio.