The Fuel Trim Cylinder Balance diagnostic detects a rich or lean cylinder to cylinder air/fuel ratio imbalance in each bank. The diagnostic monitors the pre-catalyst heated oxygen sensor (HO2S) signal's frequency and amplitude characteristics by calculating an accumulated voltage over a predetermined sample period. An imbalance is indicated when multiple samples of the accumulated voltage are consistently higher than the desired value.
Here is some GM info that may help you.
03-06-04-030G: Various Driveability Symptoms Due to Clogged Fuel Injectors, MIL/SES DTCs P0171, P0172, P0174, P0300, P1174, P1175 (Clean Fuel Injectors and/or Perform Injector Test with AFIT CH-47976) - (Apr 22, 2009)
This bulletin is being revised to update the model year to 2009 and to provide applicable engine RPO table. Please discard Corporate Bulletin Number 03-06-04-030F (Section 06 -- Engine/Propulsion System).
LH6, LS2, LQ4, LM7, LR4, L33, LQ9, L31, LU3, LL8, LK5, L52, L18
LH6, LS2, LQ4, LM7, LR4, LY2, LY5, L76, L92, LU3, LLR, LLV, LL8, L18
LH8, LS2, L92, LY2, LY5, LY6, LH6, LFA, LU3, L18
LH8, LS2, LH6, LY2, LFA, LY5, LU3, L18
Some customers may comment on any of the following various driveability symptoms:
Due to various factors, the fuel injectors may become restricted. Extensive testing has demonstrated that fuel related issues are the cause of clogged injectors. At this point, no specific fuel, fuel constituent, or engine condition has been identified as causing the restriction. The restriction causes the engine to operate at a lean air fuel ratio. This may either trigger the MIL to illuminate or the engine to develop various driveability symptoms.
Fuel injector restrictions, deposits can be cleaned on the vehicle using the following procedure. Under NO circumstances should this procedure be modified, changed or shortened. As a long term solution, and to prevent reoccurrence, customers should be encouraged to use Top Tier Detergent Gasoline . For further information on Top Tier detergent gasoline and fuel retailers, please refer to the following Corporate Bulletin Numbers: