Diagnostic code
P0171 Code: System Too Lean Bank 1
P0171 means the engine computer is adding extra fuel because bank 1 is running lean. In plain terms, the engine is getting too much air, not enough fuel, or incorrect sensor information. Vacuum leaks, intake leaks, fuel delivery issues, and
Can I drive?
A short drive may be possible, but diagnose it soon because a lean engine can run hot, hesitate, or misfire under load.
Repair range
$80-$900
Scanner note
Basic OBD-II scanner with live data
Plain-English Meaning
P0171 means the engine computer is adding extra fuel because bank 1 is running lean. In plain terms, the engine is getting too much air, not enough fuel, or incorrect sensor information. Vacuum leaks, intake leaks, fuel delivery issues, and dirty airflow sensors are common places to start.
Common Causes
Symptoms
- Rough idle
- Hesitation on acceleration
- Hard starting
- Reduced fuel economy
Diagnostic Steps
- 1Review freeze-frame data and fuel trims
- 2Inspect intake hoses and vacuum lines
- 3Smoke-test the intake if no leak is visible
- 4Clean or test the mass airflow sensor
- 5Check fuel pressure while the engine is under load
Confusable And Related Codes
P0174
Compare →P0174 means bank 2 is running lean and the computer is adding fuel to compensate. It is common on V-style engines when unmetered air enters one side of the intake, fuel delivery is weak, or the mass airflow reading is inaccurate for the act
P0300
Compare →P0300 means the engine is misfiring randomly or across multiple cylinders instead of one clearly identified cylinder. Ignition, fuel, air leaks, compression problems, or timing issues can all interrupt combustion and trigger this code.
P0101
Compare →P0101 means the mass airflow sensor signal does not match what the engine computer expects for current operating conditions. The sensor may be dirty or faulty, but intake leaks, wiring issues, and restricted airflow can create the same mism
P0507
Compare →P0507 means the engine idle speed is higher than the computer is trying to command. Extra air entering the engine, throttle body buildup, idle control faults, or an idle relearn issue can all create a high idle condition.
FAQ
Can P0171 damage the engine?
It can if the engine is driven while very lean, misfiring, or overheating.
Is P0171 always an oxygen sensor?
No. Oxygen sensors report the lean condition, but vacuum leaks and airflow problems are often more likely.
Why does P0171 show up at idle?
Vacuum leaks have a larger effect at idle because total engine airflow is low.
This page is educational and is not a substitute for hands-on vehicle diagnosis. Source notes: Code meaning verified against OBD-II reference sources; explanation is original.