AutoSense AI Knowledge Base
P0171 Code: System Too Lean Bank 1
P0171 means the engine is running too lean on bank 1, often from extra air, not enough fuel, or incorrect sensor data.
The P0171 code means the engine computer is adding more fuel than normal because it sees too much air or not enough fuel in the mixture. Bank 1 is the side of the engine that contains cylinder 1.
Lean conditions can cause rough running, hesitation, higher engine temperatures, and long-term engine or catalytic converter damage if ignored.
Symptoms
- Check engine light
- Rough idle
- Hesitation during acceleration
- Poor fuel economy
- Engine surging
- Hard starting
Common Causes
- Vacuum leak
- Dirty or failing mass airflow sensor
- Weak fuel pump
- Clogged fuel injector
- Exhaust leak before the oxygen sensor
- Faulty oxygen sensor
Severity
Moderate to high. A mild lean condition may be drivable, but a severe lean condition can cause overheating, misfires, and converter damage.
Typical Repair Costs
$50 to $1,200
- Vacuum hose repairs can be inexpensive if the leak is easy to access.
- Mass airflow sensor cleaning or replacement often ranges from $20 to $400.
- Fuel pump or injector repairs can push the cost much higher.
Frequently Asked Questions
What is the most common cause of P0171?
Vacuum leaks and dirty mass airflow sensors are common causes, but fuel delivery and oxygen sensor issues should also be checked.
Can P0171 cause a misfire?
Yes. If the mixture is too lean, combustion can become unstable and lead to misfire symptoms.
Will P0171 go away on its own?
It may turn off temporarily, but the underlying condition usually returns until the air, fuel, or sensor issue is fixed.
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Rough Idle: Symptoms, Causes, and Repair Cost
A rough idle can come from air, fuel, ignition, sensor, or mechanical issues.
Poor Fuel Economy: Common Causes and Repair Cost
Poor fuel economy can come from driving conditions, maintenance, sensors, fuel mixture problems, or engine faults.
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