P0171 · Fuel system too lean, bank 1
The computer had to add more fuel than expected to maintain the target mixture on bank 1.
Part of the Fuel trim system guide.
Compare idle with higher airflow
A large positive correction mainly at idle can point toward unmetered air. Corrections that remain high across operating conditions call for a wider look at airflow measurement and fuel delivery. Use the OEM’s test conditions and limits.
One bank changes the question
A bank 1-only result can point toward something local to that side. P0171 and P0174 together make a shared intake or fuel supply issue worth checking. A scan label that mentions the mixture gives you a condition to explain.
A vehicle-specific example
GM bulletin 22-NA-171 documents a cracked intake boot on some 2017–2022 Chevrolet Colorado and GMC Canyon trucks with the 3.6L LGZ engine. An inspection or leak test can support a repair decision before any sensor replacement.