What is the cause of the P0171 fault code in the Cruze?
4 Answers
P0171 fault code indicates that the engine fuel regulation system is too lean at high speed. The following points should be noted when repairing the P0171 fault code in the Cruze: 1. Proficient use of the repair manual and diagnostic tool data stream is required to determine the fault point. Follow the steps in the repair manual for troubleshooting, and have a clear troubleshooting approach for the fault point location. 2. The description of the lean mixture fault is related to the fuel trim value and feedback compensation value, but not to the basic fuel injection duration. 3. Fuel trim includes short-term fuel trim and long-term fuel trim. The short-term fuel trim value refers to the fuel compensation value used to continuously maintain the air-fuel ratio at the theoretical value. 4. The signal from the air-fuel ratio sensor indicates whether the air-fuel ratio is rich or lean compared to the theoretical air-fuel ratio. This adjusts the fuel injection amount, decreasing it when the air-fuel ratio is rich and increasing it when the air-fuel ratio is lean. 5. Differences between engines, wear over time, and changes in fault conditions can all cause the short-term fuel trim value to deviate from the median value.
My Cruze just threw a P0171 code last week, took me three days to fix it. Simply put, it means the engine's air-fuel ratio is too lean, meaning more air is entering than fuel being injected. Common causes include: 1) Intake system leaks - cracked vacuum hoses or aging intake manifold gaskets allow unmetered air into the engine; 2) Faulty MAF sensor - carbon buildup can cause incorrect air intake readings; 3) Clogged fuel pump or dirty filter causing low fuel pressure; The most troublesome is clogged fuel injectors - my buddy's car had insufficient fuel injection triggering the check engine light. I recommend starting with a smoke test for leaks, then checking fuel trim values via OBD. If long-term fuel trim exceeds -10%, it basically confirms a lean mixture condition.
Don't panic when you encounter code P0171, it indicates a fuel system correction exceeding limits. Personal experience shows that the Cruze is most prone to failures in three areas: First, the front oxygen sensor may fail, falsely reporting oxygen levels and causing the ECU to incorrectly adjust fuel injection. Second, the carbon canister purge valve might stick in the open position, allowing fuel vapors to directly enter the engine and dilute the air-fuel mixture. The most troublesome issue is the aging fuel tank cap seal, as abnormal fuel tank pressure can also trigger this fault code. Recommended inspection sequence: After starting, smell the exhaust pipe for gasoline odor → Disconnect the carbon canister purge valve hose to listen for hissing leaks → Pay attention to whether the fuel tank cap is unusually tight when refueling. These simple tests can save significant diagnostic costs.
My Cruze also had the P0171 code repeatedly last year. The repair shop first suggested replacing the oxygen sensor, but it didn’t solve the problem; then they replaced the fuel pump, which was a waste of money. Finally, it turned out to be a small crack in the vacuum hose behind the throttle body due to rubber aging. After securing it with a zip tie, the trouble code disappeared. The lesson is not to rush into replacing parts—prioritize checking hose seals: feel around the vacuum booster hose connections, shake the PCV valve after pulling it out, and pinch the crankcase vent hose to listen for engine RPM changes. Also, check for exhaust manifold gasket leaks, as a leaking gasket can cause the front oxygen sensor to misjudge the air-fuel ratio.
