P0172: System too rich (bank 1)

How to read it

P0172 is one of the standard OBD-II trouble codes stored when the check engine light comes on. SAE J2012, the standard that defines the codes, names it “System Too Rich Bank 1”; a generic list of OBD-II codes gives the same name.

Also searched as: code P0172, P0172 code.

What the fuel system monitor checks

The federal rule requires the system to detect any malfunction of the fuel control system that raises emissions to 1.5 times the standard. Bank 1 and bank 2 are the two exhaust banks of an engine that has two, as SAE J2012’s diagrams show.

What the manual says to do

Ford’s F-150 manual says that if the indicator stays on, the vehicle should be serviced at the first available opportunity, and that continued driving with it on can mean higher emissions, lower fuel economy, rougher running and more costly repairs.

How the light goes out

Under the federal rule, the check engine light may go out once the fault has not come back during three trips in a row under similar engine conditions. The system may erase the stored code if the same code has not been registered again in at least 40 engine warm-up cycles.