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P0171: System Too Lean (Bank 1)

Engine is running with too much air for the amount of fuel being delivered.

Can I Keep Driving with Code P0171?

Yes for short trips, but extended lean operation can damage internal engine parts.

What P0171 Means

P0171 means the computer is adding extra fuel to compensate for what it sees as a lean condition on engine bank 1. The root cause is almost always unmetered air entering the engine, a fuel delivery problem, or a faulty sensor.

Common Causes

• Vacuum leak (most common)
• Dirty MAF sensor — see repair cost
• Failing fuel pump — see repair cost
• Clogged fuel filter or injectors — see repair cost

Diagnostic Tips

• Smoke test the intake system to find vacuum leaks.
• On many cars (Ford, BMW, GM), a failed PCV valve or intake gasket is the usual culprit.
• Check fuel pressure at the rail before assuming sensor failure.

Frequently Asked Questions

Other Common Codes