Code P0171 on the 2024 Honda CR-V indicates the fuel system on Bank 1 is running too lean - meaning there's too much air relative to fuel in the combustion mixture. The ECM uses oxygen sensor feedback to monitor and adjust fuel trim, storing P0171 when positive fuel trim exceeds acceptable limits.
Understanding Lean Conditions
The ideal air-fuel ratio is approximately 14.7:1 (stoichiometric). When actual mixture is leaner (more air/less fuel), the ECM adds fuel via positive fuel trim. P0171 sets when long-term fuel trim exceeds approximately +20 to +25%, indicating the ECM has reached its correction limit.
Symptoms of Lean Running
A lean condition may cause rough idle, hesitation during acceleration, reduced power, and potential engine overheating. You might notice the engine running hotter than normal or pinging (detonation) under load. In some cases, there are no obvious symptoms until the code sets.
Common Causes
The most common causes are vacuum leaks (unmetered air entering after the MAF sensor), dirty or failing MAF sensor, weak fuel pump, clogged fuel filter, or faulty oxygen sensor providing incorrect feedback. Intake gasket leaks and PCV system issues can also cause lean conditions.
Diagnostic Strategy
Check freeze frame data to understand when the lean condition occurs. Monitor short-term and long-term fuel trims at idle and under load. Perform smoke test for vacuum leaks. Clean or test MAF sensor. Verify fuel pressure meets specification.