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I am consistently getting engine code P0171 System too lean. I inspected and found no obvious leaks in vacuum or the air intake. I have replaced the upstream O2 sensor. What should I try next?
This may be useful for diagnosing the problem: I cleared the codes shortly before driving over 200 miles, and the check engine light stayed off for the duration of the drive while on the highway. Once I got off the interstate, though, it came on after driving through town for five to ten minutes. It appears that the system is too lean in city drivng situations only.
Thanks in advance.
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The light came on once off of the highway and driving for a bit a city speeds, because in order for the code to be set again, the vehicle must go through a "drive cycle" and get the message moniters ready.
I'll take a few quotes from a few documents that may get you in the right direction
On rare occasions, a SES light may be experienced due to a P0171 DTC. This DTC could be a result of an unseated oil dipstick or air intake snorkel, which can cause the engine to draw in air that is not metered by the MAF sensor, resulting in a P0171.
On rare occasions, a SES light and P0171 DTC may be experienced shortly after installing a GM Performance Parts Air Induction Kit. This may be the result of unmetered air entering the engine after the kit is installed.
If the SI diagnostics do not isolate a cause for this concern, inspect the air intake system for obvious loose clamps/connections between the MAF sensor and throttle body, and inspect the PCV fresh air hose for a poor connection. If nothing obvious is found, also inspect the throttle body adapter to ensure that it is fully seated over the throttle body inlet seal by inspecting for air gaps at the top of the adapter slits. This can be inspected by using a flashlight and/or probing the top of each adapter slit with a toothpick to ensure that there are no openings that would allow unmetered air into the engine. If an air gap is found, remove the adapter, ensure that the throttle body seal is positioned correctly, reposition the seal and adapter until no air gaps are present, and resecure the adapter to the throttle body for evaluation.
Some customers may comment on the check engine light being illuminated.
A scan tool may reveal DTC P0171, P0300 or P1174 set as current or in history.
This condition may be caused by the plugging of one or more of the injector director plate orifices which results in a lean condition.
Correction Important:This condition cannot be corrected by cleaning the injector(s). Important:Reprogramming must be done using the remote method.
Perform an injector balance test using the Active Fuel Injector Tester (AFIT), CH-47976. Refer to the Fuel Injector Diagnosis (w/CH47976) procedure in SI. If any injector is identified as having a lean condition, replace all four injectors with the revised injectors. After installing the new injectors, reprogram the ECM with updated calibration files using the TIS2WEB Service Programming System (SPS) application. There are two calibration part numbers that are valid for "Engine Operation". Select the part number with the description that reads for vehicles with second design injector. The injector has a dark blue overmold color for this repair. Important:The fuel injectors must be replaced and the new calibration files must be installed to ensure a complete repair. Failure to perform both repairs will result in the customer returning with the same condition.
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:[align=left]
04-06-04-047G (U.S. Only)[/align][align=left]
05-06-04-022D (Canada ONLY)[/align]Notice:GM UPPER ENGINE AND FUEL INJECTOR CLEANER is the only injector cleaning agent approved for use with General Motors fuel system components. Other injector cleaners may cause damage to plastics, plated metals or bearings. General Motors has completed extensive laboratory testing of GM Upper Engine and Fuel Injector Cleaner, and can assure its compatibility with General Motors fuel system components, as long as the cleaning procedure is followed correctly.
Injector Cleaning Procedure
The following tools, or their equivalent, are required:[align=left]
CH-47976 Active Fuel Injector Tester (AFIT)[/align][align=left]