P0171: System Too Lean (Bank 1)
Severity: Moderate
What it means
The engine is getting too much air or too little fuel.
Common symptoms
- Rough idle
- Hesitation
- Possible misfires
Common causes
- Vacuum leak
- Dirty mass airflow (MAF) sensor
- Weak fuel pump or clogged filter
- Intake leak after the MAF sensor
What to check first
- Inspect vacuum hoses for cracks
- Check the air intake boot between the filter and engine
- Clean the MAF sensor with MAF cleaner
Causes vary by vehicle. Confirm with testing before replacing parts.
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