P0171 - System Too Lean (Bank 1)

The engine is running lean on bank 1.

Code Meaning

The engine is running lean on bank 1.

What You May Notice

• Rough idle or light stumble
• Hesitation on tip-in or light acceleration
• Higher-than-normal fuel trims
• Possible pinging or lack of power under load

Common Causes

Quick Checks

• Check fuel trims (STFT/LTFT)
• Inspect intake/vacuum hoses
• Clean/inspect MAF and air filter
• Check fuel pressure
• Check for exhaust leaks upstream

Bank 1 Air Metering / Fuel Trim Checks

• Review short- and long-term fuel trims at idle and cruise
• Inspect MAF signal plausibility before replacing sensors
• Check upstream O2 or A/F sensor response on the affected bank
• Verify there is no shared ground or connector issue skewing sensor data

Likely Repairs

Use test results to confirm the fault before pricing the repair.

Related Codes

Next Steps

Move from the code to a diagnosis path, then into repair pricing once the fault is confirmed.