P0171
System Too Lean (Bank 1)
Quick answer: P0171 means system Too Lean (Bank 1). Fixing the underlying cause typically runs $130 to $910 at an independent shop. Drive gently, service soon.
- Severity
- Moderate
- Safe to drive?
- Drive gently, service soon
- Typical repair
- $130 to $910
- Most likely cause
- A vacuum leak: cracked intake boot, brittle PCV hose, split intake manifold gasket, or a leaking PCV valve (the leading cause by a wide margin)
What P0171 means
The oxygen sensor is telling the computer there is too much air and not enough fuel in the exhaust from bank 1 (the side with cylinder 1). The computer keeps adding fuel to compensate, and when it runs out of adjustment range it sets P0171. This is almost never a fuel problem: it is usually air sneaking in somewhere after the sensor that measures it.
Common symptoms
What drivers usually notice with this code.
- Rough or hunting idle that smooths out once you are moving
- Hesitation or a flat spot on light acceleration
- A faint hissing or whistling from the engine bay at idle (the vacuum leak itself)
- Slightly worse fuel economy
- Occasional stalling when coming to a stop
Common causes
Ranked from most to least likely.
- 1A vacuum leak: cracked intake boot, brittle PCV hose, split intake manifold gasket, or a leaking PCV valve (the leading cause by a wide margin)
- 2A dirty or contaminated mass airflow (MAF) sensor under-reporting incoming air
- 3A leaking or stuck-open purge valve pulling extra air through the evap system
- 4Weak fuel pressure from a tired fuel pump or a clogged fuel filter
- 5Dirty or partially clogged fuel injectors
- 6An exhaust leak upstream of the oxygen sensor, letting outside air reach the sensor
Can I keep driving?
Yes, usually for a few weeks, but a lean mixture runs the engine hot and can eventually damage pistons and the catalytic converter, so do not let this one sit for months.
Severity: Moderate. A flashing check-engine light always means stop, whatever the code says.
Ballpark cost
What P0171 usually costs to fix
A range, not a quote. What you pay depends on your vehicle, your area, and which of the causes above turns out to be the real one.
Typical parts and labor at an independent shop. Dealer rates run higher.
That spread is wide on purpose. P0171 points at a system, not a single part, so the real answer depends on what the diagnosis finds. Use the range to know what to expect. If an estimate comes in higher, it usually means the specific repair is more involved, and it is always fair to ask what is included.
Next steps
What to do next
A smoke test is the right first move and typically runs $75 to $150; it finds vacuum leaks in minutes instead of by guesswork. Cleaning the MAF sensor is a cheap and worthwhile step at the same time. Be skeptical if a shop's first suggestion is replacing the oxygen sensor: the sensor is usually reporting the truth, and swapping it does not fix the leak.
Walk in informed
Ask for the diagnosis in writing and which test confirmed it, so you understand exactly what is being fixed. Fixxr shows you what the job typically costs near you, so you can approve the work with confidence.
Sources & further reading
- NHTSA — Check for vehicle safety recalls — look up open recalls for your vehicle by VIN, free
- FTC — Auto repair basics — your consumer rights at the repair shop
- AAA — Car repair and maintenance costs — independent guidance on what repairs should cost
Cost ranges and guidance reviewed July 2026.
Keep exploring
Related symptoms
P0171 FAQ
P0171 questions, answered
Can I drive with a P0171 code?
Yes, usually for a few weeks, but a lean mixture runs the engine hot and can eventually damage pistons and the catalytic converter, so do not let this one sit for months.What does the P0171 code mean?
The oxygen sensor is telling the computer there is too much air and not enough fuel in the exhaust from bank 1 (the side with cylinder 1). The computer keeps adding fuel to compensate, and when it runs out of adjustment range it sets P0171. This is almost never a fuel problem: it is usually air sneaking in somewhere after the sensor that measures it.What are the most common causes of a P0171 code?
The most likely causes, roughly in order, are a vacuum leak: cracked intake boot, brittle PCV hose, split intake manifold gasket, or a leaking PCV valve (the leading cause by a wide margin); a dirty or contaminated mass airflow (MAF) sensor under-reporting incoming air; a leaking or stuck-open purge valve pulling extra air through the evap system; weak fuel pressure from a tired fuel pump or a clogged fuel filter. A smoke test is the right first move and typically runs $75 to $150; it finds vacuum leaks in minutes instead of by guesswork. Cleaning the MAF sensor is a cheap and worthwhile step at the same time. Be skeptical if a shop's first suggestion is replacing the oxygen sensor: the sensor is usually reporting the truth, and swapping it does not fix the leak.How much does it cost to fix a P0171 code?
Fixing the underlying problem behind a P0171 code typically runs $130 to $910 at an independent shop, including parts and labor. The exact figure depends on your vehicle and which part turns out to be at fault.
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