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Ken, ASE Certified Technician
Category: Chevy
Satisfied Customers: 754
Experience:  GM Certified Technician, 25 Years Automotive Experience
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fuel trim to lean bank 2

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fuel trim to lean bank 2
Hi and thanks for your question! I have seen the intake gasket leak and set this code. There is also a bulletin on this problem. Ken
Cold Engine Idle Misfire or DTCs P0171 P0174

Models:2002-2005 Cadillac Escalade
1999-2005 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe, Trailblazer
1999-2005 GMC Savana, Sierra, Yukon
2003-2005 Hummer H2


The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.


99 through 05 GEN III truck engines may experience any of the following:

  1. A cold rough idle that diminishes as the engine warms up.
  2. Possible DTCS P0171, P0174, or P0300.
  3. Random misfires at idle.


The intake gasket seals may be leaking around the intake ports, causing a lean condition. The intake gasket seals may leak around the bottom side of the port, making it a challenge to detect the vacuum leak. The technician may also notice lower than normal MAF readings if the intake seals are leaking.

  1. If leaking intake gasket seals are found, replace the intake gaskets. During the repair be sure to use the current GMSPO part number for replacement intake gaskets. The current GMSPO part number for intake gaskets will have a teal green intake gasket seal. The old version of the intake gaskets were orange in color. Use only the teal green colored gaskets for a repair.
  2. The intake plenum should also be checked for excessive warpage that may cause an uneven clamping pressure of the seal. If the plenum is found to be warped it will need to be replaced. Service Information states, "An intake manifold with warpage in excess of 3 mm (0.118 in) over a 200 mm (7.87 in) area should be replaced". Intake warpage is measured at the gasket sealing surfaces, and should be measured within a 200 mm (7.87 in) area. This measurement is across only two of the intake runner port openings. Measurements taken across the entire distance of all four intake runner ports will lead to unnecessary manifold replacements.


Customer: replied 7 years ago.
is there any other reasons for this code
The #1 reason is the intake manifold. Low fuel pressure , a plugged fuel filter or a plugged injector can also set a p0174. I have seen a skewed O2 sensor set this code. You can swap the two front sensors. Put a small piece of tape on the right sensor so you don't mix them up. Have a fuel pressure tested and replace the fuel filter. Have a injector balance test done to test the injectors. Make sure you do not have a exhaust leak on that side Any fresh air will cause this code to set also. Ken
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 suppling enough fuel.
A lean condition could be present during high fuel demand.
Use a scan tool in order to review the Failure Records .
I just had a truck in this morning with lean codes. I checked the fuel pressure, it was good. Then I watched the fuel trim readings on the scan tool. They where + 12 on both sides. I sprayed some carb cleaner around the intake and in front of the intake and they went down to +2. This motor has a leaking intake gasket. Ken
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