Chevrolet / GMC / Vehicle-specific diagnosis
Colorado and Canyon P0171 + P0174: inspect connections, then calibration
GM 21-NA-105 addresses both lean codes occurring together.
Check the vehicle first.
- Vehicles
- 2020–2021 Colorado/Canyon, LGZ; built through May 1, 2021
- Evidence boundary
- Reviewed May 2021 bulletin
Four connections before programming
Inspect PCV/oil-separator connections, oil-cap seating, a cracked filler adapter and dipstick seating. GM then requires checking/updating ECM software whether or not an inspection concern was found.
What happens after the update?
| Result or mismatch | Next decision |
|---|---|
| No codes return | The bulletin’s verification is satisfied. |
| Codes return | Continue the specific GM service-information diagnosis. |
| Only one lean code or different engine/build | Do not assume this paired-code case fits. |
What should the repair record contain?
Editorial checklist: request the inspection findings, the installed calibration identifier and the result of the post-repair check. “Updated computer” describes an operation, but does not tell you whether the original complaint returned. If sensors or injectors are also quoted, ask for the separate test result supporting those parts. The paired code names alone are not that explanation.
An extinguished lamp is not inspection readiness
The bulletin notes that code clearing resets inspection status. The 2021 Colorado manual explains that incomplete emissions checks can prevent an inspection pass after servicing; routine driving may be needed before readiness returns. Ask the shop to report readiness separately from “no current codes.”
If the lamp flashes while driving
For the 2021 Colorado, Chevrolet advises reducing speed and avoiding hard acceleration and grades. If flashing continues, park safely; follow the manual’s restart/service guidance. A steady lamp still needs diagnosis. Canyon and other model-year owners should follow their own manual.
Source documents
- 21-NA-105
Source reviewed .
- 2021 Colorado owner manual — warning lamps and emissions readiness
Source reviewed .