PROBLEMS & DIAGNOSTICS
2015 Chevrolet Silverado 1500 P0171 & P0174 Lean Codes
P0171 means the engine computer sees a lean condition on Bank 1; P0174 is the corresponding Bank 2 code. They do not automatically mean bad oxygen sensors.
Confirm the engine, trim, drivetrain, market and installed equipment before using a part number, capacity or repair procedure.
Lean-code diagnostic patterns
| Observed pattern | Potential direction |
|---|---|
| Lean trims most pronounced at idle | Possible vacuum/intake leak |
| Lean under load or acceleration | Fuel delivery or measurement concern |
| Both banks affected | Shared intake, fuel or sensor cause |
| Only one bank affected | Bank-specific air/exhaust/injector issue |
Patterns are not definitive diagnoses; live data and GM diagnostic procedures decide.
Why the codes appear
The powertrain module may add fuel when measured exhaust oxygen indicates the mixture is too lean. Air leaking in after the measured intake path, fuel delivery that cannot meet demand, some sensor errors and exhaust leaks can produce similar codes. Both banks appearing together often calls for checking shared air and fuel conditions; one bank may call for a more localized inspection.
A sensible diagnostic sequence
Record codes and short- and long-term fuel trims at warm idle and steady higher rpm. Inspect intake ducts, hoses, vacuum/PCV plumbing and obvious exhaust leaks. Compare commanded versus measured fuel pressures when necessary. Do not smoke-test a fuel system or open direct-injection pressure lines without the approved safety procedure.
- P0171 is Bank 1; P0174 is Bank 2.
- A lean code can follow a misfire; diagnose companion codes together.
- Avoid buying two oxygen sensors before checking for unmetered air.
Use the correct model-year manual and current service information. Stop if instructions or safety precautions are unclear, and use a qualified technician for work you cannot verify.
References and further reading
This independent guide is not endorsed by the vehicle manufacturer. Let us know if you spot an error.