DTC P0174 - FUEL TRIM SYSTEM LEAN BANK 2 GMC Envoy I

Note. For circuit reference, see WIRING DIAGRAMS - 4.3L article.

Circuit Description

VCM reads HO2S signal voltage and adjusts fuel delivery based on this voltage. A change made to fuel delivery is indicated by Long Term (LT) and Short Term (ST) fuel trim values.

ST fuel trim values change rapidly in response to HO2S signal voltages. These changes fine tune engine fueling. LT fuel trim values changes in response to trends in ST fuel trim. LT fuel trim makes coarse adjustments to fueling in order to re-center and restore control to ST fuel trim. LT and ST fuel trim can be read by using a scan tool.

Ideal fuel trim value is about 128. Fuel trim value more than 128 indicates that VCM is adding fuel to compensate for a lean condition. Fuel trim less than 128 indicates that VCM is reducing amount of fuel to compensate for rich condition. DTC will set if VCM detects an excessively rich or lean condition.

Conditions for setting DTC

1. No IAC DTCs set at idle.
2. No ECT, EGR, HO2S, IAT, MAF, MAP, TP or VSS sensor DTCs set.
3. No EVAP or voltage system DTCs set.
4. No misfire DTCs set.
5. Engine speed 575-4500 RPM.
6. BARO is greater than 70 kPa.
7. ECT is greater than 140°F (60°C) but less than 210°F (99°C).
8. MAP greater than 20 kPa, but less than 99 kPa.
9. IAT greater than -4°F (-20°C), but less than 159°F (70°C).
10. MAF us greater than 3 gm/s, but less than 150 gm/s.
11. Vehicle speed less than 85 MPH.
12. Average short term fuel trim is not greater than 115.