maybe since you did head gasket , also what vehicle do you have ? engine ?
#PIP5028D: MIL due to DTC P0128 and/or P0171 and No Engine Performance Concerns - (Dec 5, 2012)
If this concern is experienced, perform SI diagnosis and repair as necessary. IfSI diagnosis does not isolate the cause of this concern, reprogram the ECM with thelatest calibrations from TIS2Web, which contain improvements that may repair thisconcern. At this time, the updated Engine Diagnostic calibration is titled: "NewCalibration with Diagnostic Enhancements for DTCs P0128 and P0171."
If SI diagnosis does not isolate the cause of a P0171 DTC and the updated ECM calibrationmentioned above does not repair it, perform the following suggestions as necessary:
1. Inspect the engine for any obvious oil leaks, which may allow the engine to draw inunmetered air through the PCV system. Repair any obvious oil leaks and re-evaluatethe concern.
2. If this happened shortly after an oil change, closely inspect the oil fill cap/neckand oil dipstick to ensure that they are seated properly.
3. Use the CH-44175-1 handheld tester to test the ethanol content of the fuel. As outlinedin the Alcohol / Contaminants-in-Fuel Diagnosis Procedure in SI, it should be 15%or less.
4. Check for unmetered air/vacuum leaks by using the EVAP smoke machine to induce smokeinto the engine, exhaust, and air intake system as outlined in the latest versionof PIP4925. Please note that it is normal to see a small amount of EVAP smoke escapefrom the AIR pump during this test. If EVAP smoke is noted in any other location,repair as necessary and re-evaluate the concern.
5. Inspect the air filter condition to ensure that it is a factory filter and that noneof the pleats are damaged, etc. If a concern is found, replace the air filter andre-evaluate the concern.
6. Inspect the inside of the air cleaner opening before the MAF sensor for any sign ofcasting flash, etc., which may cause turbulence and skew the MAF sensor input. Ifflashing is found, trim and remove it as necessary, and re-evaluate the concern.
7. If the concern is currently happening (LT Fuel Trims in the Mid-Teens or Greater)while at a hot idle, plug all vacuum lines (brake booster, EVAP purge pipe, etc.),and re-evaluate the LT fuel trims while at a hot idle. If the LT fuel trims decreaseto 10% or less, the engine may be drawing in unmetered air through the related componentand replacement of that component (brake booster, brake booster check valve, EVAPpurge valve,etc.) may be required.
8. For Equinox and Terrain Models Only, also inspect the air cleaner lid to ensure thatit is correct by confirming the height of the MAF sensor as shown below. If the correctair cleaner lid is installed, you should be able to place a 6 mm allen wrench/bitbetween the MAF sensor and air cleaner housing as shown below to feel a slight dragor if you use a 7/32" allen wrench/bit you will feel a small amount of play/clearance. If theincorrect air cleaner lid is installed, it will be obvious when the allen wrench/bitis installed because there will be about an additional 1/8" of clearance present. If an incorrect air cleaner lid is found, replace the air cleaner assembly usingthe correct part number listed in the parts catalog, re-evaluate the concern, andsubmit a product report with photos by following the latest version of 07-00-89-036.
The engine control module (ECM) controls a Closed Loop air/fuel metering system in order to provide the best possible combinationof driveability, fuel economy, and emission control. The ECM monitors the heated oxygen sensor (HO2S) signal voltage, andadjusts the fuel delivery based on the signal voltage while in Closed Loop. A change made to the fuel delivery changes thelong and short term fuel trim values. The short term fuel trimvalues change rapidly in response to the HO2S signal voltages. These changes fine tune the engine fueling. The long term fueltrim values change in response to trends in the short term fuel trim The long term fuel trim makes coarse adjustments to fuelingin order to re-center and restore control to short term fuel trim. The ideal fuel trim values are around 0 %. A positive fueltrim value indicates that the ECM is adding fuel in orderto compensate for a lean condition. A negative fuel trim value indicates that the ECM is reducing the amount of fuel in orderto compensate for a rich condition.