The 1947 - Present Chevrolet & GMC Truck Message Board Network

Your air filter chould be over oiled transfering the oil onto the MAF sensor GM has a TSB on this. Check for vacuum leaks like broken vacuum lines, leaking intake gaskets, EGR tube O-ring leaking at the manifold, leaking throttle body gasket, Check all the piping between the MAF sensor and throttle body.

Here the test Procedure for codes P0171 & P0174 bank 1&2 lean

CIRCUIT DESCRIPTION
The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals without oxygen sensor (O2S) input. During Closed Loop, the O2S inputs are added and used by the PCM to calculate short and long term fuel trim fuel delivery adjustments. If the O2S indicate a lean condition, fuel trim values will be above 0 percent . If the O2S indicate a rich condition, fuel trim values will be below 0 percent . Short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. If the PCM detects an excessively lean condition, DTC P0171 or P0174 sets.

CONDITIONS FOR RUNNING THE DTC

DTCs P0101, P0103, P0108, P0135, P0137, P0141, P0200, P0300, P0410, P0420, P0430, P0440, P0442, P0443, P0446, P0449, P0506, P0507 or P1441 are not set.
The engine coolant temperature (ECT) is between 75-115°C (167-239°F) .
The intake air temperature (IAT) is between -20 to +90°C (4-194°F) .
The manifold absolute pressure (MAP) is between 26-90 kPa (3.7-13 psi) .
The vehicle speed is less than 137 km/h (85 mph) .
The engine speed is between 400-3,000 RPM .
The barometric pressure (BARO) is more than 74 kPa (10.7 psi) .
The mass airflow (MAF) is between 5-90 g/s .
The fuel level is more than 10 percent .
The throttle position (TP) is less than 90 percent .
CONDITIONS FOR SETTING THE DTC

The average long term fuel trim cell value is above 23 percent .
All of the above conditions are present for 6 seconds .

ACTION TAKEN WHEN THE DTC SETS

The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
CONDITIONS FOR CLEARING THE MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
DIAGNOSTIC AIDS

The system will go lean if an injector is not supplying enough fuel.
A lean condition could be present during high fuel demand.
Use a scan tool in order to review the Failure Records.

TEST DESCRIPTION

The numbers below refer to the step numbers on the diagnostic table.

5. If conditions were not corrected, refer to Fuel System Diagnosis for a possible fuel problem. See: Component Tests and General Diagnostics\Fuel System Diagnosis
6. If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be the problem.