What does code P0171 mean on a Honda and is it safe to drive?
P0171: System Too Lean (Bank 1). Here's what it means on your Honda, what usually causes it, what repairs typically cost, and how safe it is to keep driving.
What this code means
The engine is getting too much air relative to fuel. The O2 sensor sees excess oxygen in the exhaust and the PCM is adding more fuel than normal to compensate.
Common causes for your Honda
- Dirty or faulty mass airflow (MAF) sensor
- Vacuum leaks (PCV hose, intake gasket, brake booster)
- Weak fuel pump or clogged fuel filter
- Leaking or stuck open fuel injectors (less common)
Symptoms
- Check Engine Light
- Rough idle, hesitation, lack of power
- Possible spark knock under load
- Poor fuel economy
Typical fixes
- Clean or replace MAF sensor
- Locate and seal vacuum leaks
- Replace fuel filter / test fuel pressure
- Smoke test intake system
Repair cost range
For a Honda, repairs for P0171 often fall between $50 and $500, depending on the cause and whether you use OEM or aftermarket parts. Labor rates vary by location.
Known issues on Honda
Honda P0171 on K24 engines almost never traces to the MAF sensor—Honda's MAF calibration is robust. Focus instead on vacuum leaks: the PCV hose routing from the valve cover to the intake manifold cracks at 80k+ miles on R18 and K24 engines; a split PCV hose is the most common cause. On Accord 2.4 with IMRC (Intake Manifold Runner Control), the vacuum actuator diaphragm tears and leaks. Honda uses a narrowband MAP+MAF hybrid metering strategy; a smoke test of the intake tract is the most efficient diagnostic.
Most commonly affected models