P0171
Moderate severityFuel System Too Lean (Bank 1)
Drivable short-term, but a lean mixture runs hot and can cause damage over time. Get it checked within a week; sooner if you feel rough idle, hesitation or stalling.
Stop driving if: the check engine light is flashing, or the car starts running noticeably worse
What does the P0171 code mean?
The P0171 code means the engine on Bank 1 is running “lean” — there is too much air or not enough fuel in the mixture. The computer notices it is adding fuel to compensate beyond its normal limit, so it sets the code.
“Bank 1” is the side of the engine with cylinder 1. On V6/V8 engines this code often appears together with P0174 (the same problem on Bank 2), which usually points to a shared cause.
Can you keep driving with a P0171 code?
Yes, with care. A short-term lean condition usually won’t strand you, but over time it raises combustion temperatures and can cause misfires or damage. Get it checked within a week, and sooner if the car idles rough, hesitates, or stalls.
What causes a P0171 code?
Listed in the order most shops would check them — cheapest and most likely first, not as statistical odds. The real cause varies by year, make, model and engine.
- Faulty O2 sensor or PCV problemCheck 1st
- Weak fuel delivery (pump, filter, injectors)Check 2nd
- Dirty or failing MAF sensorCheck 3rd
- Vacuum leak (cracked hose or intake gasket)Check last
How to diagnose a P0171 (check these first)
- Inspect vacuum hoses and the intake boot for cracks or loose connections.
- Clean the MAF sensor with MAF-safe cleaner (never touch the wire).
- Check the gas cap and the PCV valve.
- Scan for P0174 — if both appear, suspect a shared cause like a big vacuum leak or the MAF.
P0171 repair cost
Typical US ranges including parts and labor (varies by vehicle):
Costs vary a lot by vehicle and region. These are typical US ranges including parts and labor — treat them as a ballpark for the conversation with your shop, not a quote.
| Vacuum hose / intake gasket | – 0 |
| MAF sensor | – 0 |
| Fuel pump / filter | 0 – 0 |
Tools & parts that help
Start cheap: a can of MAF sensor cleaner and a scanner often reveal the problem before you replace anything expensive.
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P0171 — Frequently asked questions
Is it safe to drive with a P0171 code?
Short-term yes, but check it within a week. A lasting lean condition runs hot and can cause misfires or engine damage.
What causes a lean code like P0171?
Most often a vacuum leak or a dirty mass air flow (MAF) sensor; sometimes weak fuel delivery or a bad O2 sensor.
Can a dirty MAF sensor cause P0171?
Yes. A dirty MAF under-reports airflow, so the computer adds too little fuel and the mixture goes lean. Cleaning it often fixes the code.
Why do P0171 and P0174 appear together?
Because both banks read lean, the cause is usually shared – typically a large vacuum leak or a MAF sensor problem.
Related codes
General guidance based on the standard SAE definition of the P0171 code. A real diagnosis depends on your make, model, year, engine and other symptoms. This is not a substitute for a professional inspection — when in doubt, have a technician confirm the cause before replacing expensive parts.