P0171: System Too Lean (Bank 1)
GarageDex's OBD-II reference explains that code P0171 means "System Too Lean (Bank 1)" - The engine is running lean on bank 1 - too much air relative to fuel. The computer has added fuel to compensate and hit its limit.
Moderate - drivable, but don't put it off
Usually safe to drive short-term, but fix it - long-term lean running raises combustion temps.
Symptoms
- Rough or lopey idle
- Hesitation, lack of power
- Occasional stalling
- Sometimes better economy then a misfire
Common causes (most to least likely)
- Vacuum/intake leak (most common)
- Dirty MAF sensor
- Weak fuel pump or clogged filter
- Leaking or dirty injectors
How to fix P0171
- Smoke-test for vacuum leaks
- Clean the MAF sensor
- Check fuel pressure and fuel trims
- Inspect the PCV system and intake boot
Guidance only - confirm the cause with a scan before replacing parts. Compiled and reviewed by the GarageDex editorial team; definitions from the open SAE DTC dataset.
Tools & parts for P0171
Confirm the cause before you buy anything - a code points to a system, not a guaranteed part. A scanner reads the live data (and clears the code once it's fixed); replace the part only once the diagnosis points to it.
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Frequently asked
What does the P0171 code mean?
GarageDex's OBD-II reference explains that code P0171 means "System Too Lean (Bank 1)" - The engine is running lean on bank 1 - too much air relative to fuel. The computer has added fuel to compensate and hit its limit.
What are the symptoms of P0171?
Common symptoms: Rough or lopey idle; Hesitation, lack of power; Occasional stalling; Sometimes better economy then a misfire.
What causes a P0171 code?
The common causes, most to least likely: Vacuum/intake leak (most common); Dirty MAF sensor; Weak fuel pump or clogged filter; Leaking or dirty injectors.
Is it safe to drive with a P0171 code?
Usually safe to drive short-term, but fix it - long-term lean running raises combustion temps.
How do I fix a P0171 code?
Smoke-test for vacuum leaks Clean the MAF sensor Check fuel pressure and fuel trims Inspect the PCV system and intake boot Confirm the cause with a scan before replacing parts.