P0172 System Too Rich (Bank 1)
The engine is getting too much fuel for the amount of air, and the computer has reached its limit for trimming fuel away on bank 1.
Common causes
- Leaking or stuck-open fuel injector
- Faulty fuel pressure regulator
- Dirty or faulty MAF sensor
- Faulty coolant temperature sensor
- Clogged air filter
Symptoms
- Poor fuel economy
- Black smoke
- Fuel smell
- Rough idle
- Fouled spark plugs
Can I drive with it?
Usually safe to drive short term, but running rich wastes fuel and can damage the catalytic converter.
Tip: A rich code on both banks (P0172 and P0175) points to something shared, like fuel pressure or the MAF sensor.
Which scanner reads it?
Any OBD2 scanner reads it. Fuel trim and oxygen sensor live data are the key to finding the cause.
Budget tools like the ANCEL AD310 read it; tools with live data and graphing – like the BlueDriver or OBDLink MX+ – help you find the cause. Not sure which fits you? Try the Find My Scanner quiz.
In the data
How common is it? In New York City’s taxi and for-hire fleet – high-mileage cars, mostly hybrids – P0172 was the #14 code found on cars failing inspection in 2020–21 (1.3% of codes found).
Of the vehicle complaints owners filed with NHTSA from 2015 to 2025, 64 quote P0172 – most often from Honda, Kia, Chevrolet owners. Complaints lean toward serious problems, so treat this as a sign of how often the code turns up in real reports, not how often cars get it.
Both sources are compared on the Trends page.
Related codes
General information to help you understand a code – not a diagnosis. Your car’s service information or a qualified mechanic has the final word. See how we research.