P0172 Nissan Altima
System Too Rich (Bank 1) · Powertrain Code · Medium · Repair: Moderate
What is P0172?
The engine is running rich on bank 1 — too much fuel or not enough air. Common causes include leaky fuel injectors, stuck-open purge valve, or a dirty/faulty MAF sensor.
When the Nissan Altima triggers code P0172 (system too rich (bank 1)), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Nissan Altima.
This repair is rated moderate, meaning some experience and specialty tools required.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Nissan Altima.
Common Causes on Nissan Altima
- Dirty or failed MAF sensor (the #1 cause on Nissan vehicles)
- Leaking fuel injector delivering excess fuel
- High fuel pressure from faulty fuel pressure regulator
- Clogged air filter starving the engine of air
- PCV valve stuck open pulling crankcase vapors into intake
Symptoms
- Check Engine Light on
- Strong fuel smell from exhaust
- Black smoke from tailpipe
- Rough idle
- Fouled spark plugs
Notes for Nissan Altima
On Nissan vehicles, a contaminated MAF sensor is by far the most common cause of P0172; always try cleaning first.