P0171
System Too Lean (Bank 1)
Severity: moderate
Driveability: Safe To Drive
AI generated
Plain-English meaning
The engine control module (ECM) has detected that the air-fuel mixture on bank 1 is too lean, meaning there is too much air or not enough fuel.
What to check first
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What not to replace yet
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Stop driving when
If the vehicle exhibits severe hesitation, stalling, or loss of power that compromises safe driving, stop driving and have the vehicle inspected.
Related symptoms
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Owner steps
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Likely causes
Vacuum leaks
Faulty or dirty mass air flow (MAF) sensor
Clogged fuel injectors
Weak fuel pump or low fuel pressure
Faulty oxygen sensor
Dirty or faulty air filter
Exhaust leaks near oxygen sensor
Shop steps
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Follow-up questions
When did the check engine light first come on?
Have you noticed any changes in fuel economy?
Are there any unusual noises or smells from the engine?
Has any recent maintenance been performed on the vehicle?