Drive with caution — fix soon.
This code means your engine's computer has detected that the fuel mixture on bank 1 is off and it can no longer compensate to keep it balanced. It often points to an air leak, a faulty oxygen or mass airflow sensor, low fuel pressure, or dirty fuel injectors. It's a fairly common code and is usually fixable without major engine work once the root cause is found.
$100 – $600
Varies by vehicle and root cause.
For short trips, usually yes, but you shouldn't rely on it long term. A bad fuel mixture can lower your gas mileage and eventually damage the catalytic converter, so get it diagnosed within a week or two.
It depends on the cause. A vacuum leak repair or sensor cleaning may run around $100, while replacing an oxygen sensor, MAF sensor, or fuel injectors can push the total toward $600.
It's moderate. The car will usually still run and drive, but ignoring it can hurt fuel economy and lead to costlier emissions repairs down the road, so it's worth addressing promptly.
Fuel trim is how the computer fine-tunes the amount of fuel based on sensor readings. A P0170 means the computer is making large corrections and can no longer keep the mixture in the normal range.