2018 Nissan P0171: What It Means & Is It Safe to Drive?
P0171 on the 2018 Nissan: System Too Lean (Bank 1). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe 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 on the 2018 Nissan
- 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 2018 Nissan, repairs for P0171 typically fall between $50 and $500, depending on the root cause and labor rates in your area.
Known issues on Nissan
Nissan P0171 on QR25DE 2.5L engines is very commonly caused by the EVAP purge valve (canister purge solenoid) sticking open—when stuck open, it draws in a large unmetered air stream that leans out the mixture. Test the purge valve by unplugging it; if the lean condition temporarily improves, replace the valve. On VQ35DE 3.5L engines (Maxima, Murano, Pathfinder), the intake manifold collector gasket cracks at the rear cylinder bank by 90k–110k miles—requires intake removal to access and replace.
Most commonly affected models