OBD codes / P0171
P0171
SeriousSystem Too Lean (Bank 1)
P0171 is usually safe to drive with short-term, but do not ignore it. A lean mixture runs hotter and can eventually trigger misfires or, in the worst case, contribute to engine damage. Have it diagnosed soon — and because a cheap vacuum leak and an expensive fuel pump both set this code, confirm the cause before buying parts.
What this code means
Your engine constantly adjusts the air-to-fuel ratio. "Too lean" means there is too much air or too little fuel, and the computer has had to add fuel to compensate up to its limit on Bank 1 (the side with cylinder 1). The most common cause is unmetered air sneaking in — a vacuum or intake leak, or a dirty mass-airflow (MAF) sensor that under-reports airflow. It can also be weak fuel delivery: a tired fuel pump, a clogged filter, or dirty injectors. A persistent lean condition can raise combustion temperatures and, over time, lead to misfires, so it is worth chasing down.
Symptoms you might notice
- Rough or unstable idle
- Hesitation, stumble, or lack of power under acceleration
- Slightly reduced fuel economy
- Occasional surging at steady speed
- Sometimes no symptom beyond the check-engine light
What it costs to fix
Typical range: $100–$1,000 · about ~0.3–3 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Vacuum / intake leak repair (hose, gasket, PCV) | $10–$150 | ~0.5–2 hrs |
| MAF sensor (clean or replace) | $0–$350 | ~0.3–0.5 hrs |
| Fuel pump | $150–$500 | ~1–3 hrs |
| Fuel filter | $20–$120 | ~0.5–1.5 hrs |
A vacuum-leak or MAF-clean fix is often under $200; a fuel pump is the expensive end. The MAF low end can be near-zero if cleaning the sensor solves it. Diagnosis time to find a small leak can itself add labor.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0171 for my exact vehicle →
Frequently asked
Can I drive with P0171?
Short-term, usually yes — it is rarely an immediate breakdown risk. But a lean condition runs the engine hot and can lead to misfires over time, so have it diagnosed soon rather than letting it linger.
What is the most common cause of P0171?
Unmetered air is the usual culprit: a vacuum or intake leak, or a dirty MAF sensor reading low. Weak fuel delivery (pump, filter, injectors) is the next thing to check. A smoke test plus a fuel-pressure check usually settles which it is.
Will cleaning the MAF sensor fix P0171?
Sometimes — a dirty MAF is a common, cheap cause, and sensor cleaner is inexpensive. But if a vacuum leak or fuel-delivery problem is the real issue, cleaning the MAF won't help, so verify before assuming.
How much does it cost to fix P0171?
Often inexpensive — many fixes are a vacuum hose, a gasket, or a MAF clean for well under $200. It only gets costly if the cause is a fuel pump. Confirm the cause first so you don't replace parts that were fine.
Can P0171 cause a misfire?
Yes. A persistently lean mixture can lead to misfires (and codes like P0300) because some cylinders aren't getting enough fuel. Fixing the lean condition often clears the related misfire too.
Seeing P0171 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0171 for my vehicleGeneric OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.