Check Engine Code
P0171
System Too Lean (Bank 1)
What P0171 means
P0171 means the long-term fuel trim (LTFT) has pushed past ~25% trying to add fuel to compensate for what the ECM perceives as a lean condition. Almost always caused by unmetered air entering the engine downstream of the MAF sensor, or by low fuel pressure.
Vehicle-specific P0171 guides
P0171 can mean different things on different vehicles. Pick your make for engine-family specifics:
Symptoms
- Check engine light
- Rough idle, sometimes surging
- Hesitation on acceleration
- Reduced fuel economy
- Occasional misfires (P0300-series)
Likely causes (most common first)
- Vacuum leak — split intake boot, cracked PCV hose, failed intake manifold gasket
- Dirty MAF sensor
- Weak fuel pump / low fuel pressure
- Clogged fuel injector
- Failed fuel pressure regulator
- Exhaust leak before the upstream O2 sensor
- EVAP purge valve stuck open
Can I keep driving?
Yes short-term, but persistent lean operation raises combustion temperatures and can damage pistons, valves, and the catalytic converter. Don't ignore for more than a couple weeks.
Typical repair cost
DIY fixes can start near $10 (parts only). Shop repairs for P0171 typically run up to $600 depending on the underlying cause and vehicle. Start with the most common cause — Vacuum leak — split intake boot, cracked PCV hose, failed intake manifold gasket — before throwing parts at it.
Symptoms that match P0171
If you got here from a search query, one of these might describe what your car is actually doing:
Recommended parts & tools for P0171
Most common fix for P0171:
MAF sensor cleanerCompare the parts and tools that pair with AXLY:
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Related codes
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