Drive with caution — fix soon.
P0172 means the engine is running too rich on bank 1, meaning the air-fuel mixture has too much fuel or not enough air. The computer noticed it's cutting back fuel to compensate but still can't bring the mixture into the correct range. Bank 1 is the side of the engine that contains cylinder 1.
$90 – $500
Varies by vehicle and root cause.
Short-term, usually yes, but don't delay the repair. A rich mixture wastes fuel and can foul plugs and harm the catalytic converter over time.
It depends on the cause: a new air filter or sensor can be $90-$250, while an oxygen sensor, injector, or fuel pressure regulator can push the cost to $300-$500 or more.
It's moderate. It won't usually leave you stranded immediately, but ongoing rich running can damage the catalytic converter, so fix it before it escalates.
When there's too much fuel for the available air, some fuel doesn't fully burn and exits as black, sooty exhaust along with a noticeable fuel smell.