Honda P0171 Code: System Too Lean (Bank 1)

Updated October 8, 2026Sources

On this page 4 sections

Meaning: Too much air or too little fuel. The computer has reached its limit for adding fuel to compensate.
Checks to start with: Vacuum / intake leaks and the MAF sensor.
Safe to drive?: If the light is steady, Honda says to avoid high speeds and have the vehicle inspected immediately. If it starts flashing, stop safely. Running lean can overheat & misfire.

A gas cap does not cause P0171. Gas-cap trouble sets an EVAP code (P0455/P0456); P0171 is purely about the balance of air and fuel.

What P0171 means

The engine computer trims fuel up and down to hold the ideal air/fuel ratio. When it has to keep adding fuel and still reads “lean,” it hits its correction limit and sets P0171. Something is letting in unmetered air or starving the engine of fuel.

Possible causes

Vacuum / intake leak
Dirty or failing MAF sensor
Weak fuel pump / clogged filter
Leaking or clogged injectors
Faulty upstream O2 sensor

Do these checks first

Look for vacuum leaks: spray a little carb cleaner around the intake boot and PCV hoses. If the idle changes, you've found the leak.
Clean the MAF sensor with MAF-specific cleaner (never touch the wire).
Check fuel pressure and fuel trims. A weak pump shows lean trims that get worse under load.

FAQ

Is P0171 serious?

Running lean for a long stretch raises combustion temperatures and can cause misfires or long-term engine damage. If the check engine light is steady, Honda says to avoid high speeds and have the vehicle inspected immediately. If the light starts flashing, stop safely.

Can a dirty air filter cause P0171?

A clogged filter restricts airflow, which pushes the mixture rich, not lean. Look at unmetered air (leaks) and the MAF first.

Will P0171 clear itself?

Only if the cause goes away on its own, such as a hose that reseats itself. Otherwise it comes back after the next drive cycle.

Sources

Owner's manual references are to the model and year named above. Wording and procedures can differ on your Honda, so check your own owner's manual.

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