GMC-specific code — factory diagnostic data| DTC Data Sheet | |
| Code | P0171 |
| Vehicle | GMC Sierra 1500 (2007-2019) |
| Engine | 4.3L V6 / 4.8L-6.2L V8 |
| System | FUEL AND AIR METERING |
| Fault type | Performance |
| Official meaning | System Too Lean (Bank 1) |
Definition source: GMC factory description. Diagnostic guidance is based on factory-defined fault logic for this code.
Decode any GMC Sierra 1500 VIN — free recalls, specs & safety ratings — free VIN decoder with NHTSA data
Looking for the cross-vehicle definition? Read the generic P0171 article for the SAE-defined fault logic that applies to all manufacturers.
P0171 Quick Answer
P0171 on a Sierra means the PCM is adding more than 25% extra fuel to keep Bank 1 (driver side) at proper mixture. Same root cause pattern as Silverado: MAF sensor contamination first, intake manifold gasket leak second, PCV system fault third, fuel pump as a last resort. MAF cleaning resolves about 30-40% of cases for free.
What Does P0171 Mean on a GMC Sierra 1500?
The GMC Sierra 1500 (2007-2019) shares the GMT900 / K2XX chassis and Gen-IV LS engine families with the Chevy Silverado 1500. P0171 root causes match the Silverado pattern exactly. The model-specific failure modes documented below apply to all Sierra trim levels using the same engine.
Symptoms
- Check Engine Light (P0171, sometimes paired with P0174)
- Rough idle smooths above 1500 RPM
- Hesitation on tip-in
- Slight fuel economy loss
- Possible P0300 as condition worsens
Common Causes (Most Likely on This Model First)
- MAF sensor contamination. Oil mist from the PCV coats the MAF wire. Clean with CRC MAF-specific cleaner (never carb cleaner — kills the sensor).
- Intake manifold gasket shrinkage. Gen-IV LS intake gaskets shrink at the corners after 100k-150k. Smoke-test confirms.
- Cracked PCV hose / stuck-open PCV valve. Calibrated leak grows beyond fuel-trim compensation.
- Failing fuel pump or clogged filter. Returnless system should hold ~58 psi key-on. < 50 psi at WOT = pump.
- Leaking injector O-ring. Spray soapy water at injector bases with engine running.
Diagnostic Approach
- Read freeze frame, note LTFT B1 and B2. If both > +15%, leak is upstream of throttle (MAF/PCV/intake).
- Spray carb cleaner around intake with engine running. RPM change = leak found.
- Clean MAF with CRC MAF-specific cleaner. Drive 50 miles, recheck fuel trims.
- Check fuel pressure at WOT — ≥ 55 psi.
- Inspect intake gasket joints for the front and rear corners on Gen-IV LS.
Possible Fixes
| Fix | When |
|---|---|
| MAF cleaning | Always first — free, fixes ~30-40% |
| MAF sensor replacement | Cleaning didn’t help |
| Intake manifold gasket | Smoke test reveals leak |
| PCV valve + hose | Visible crack |
| Fuel pump replacement | Pressure < 50 psi at WOT |
Can I Still Drive With P0171?
Yes short-term. Extended lean operation eventually damages the catalyst — fix within a few weeks.
How Serious Is This Code?
Moderate. Lean condition compounds (P0420 eventually appears if ignored).
Repair Costs
| Repair | Cost |
|---|---|
| MAF cleaning (DIY) | $10 |
| MAF sensor | $120 – $260 |
| PCV valve + hose | $45 – $120 |
| Intake gasket set | $420 – $780 |
| Fuel pump | $580 – $950 |
FAQ
What does P0171 mean on a GMC Sierra?
The PCM is adding more than 25% extra fuel to compensate for a lean Bank 1 condition. Leading causes are MAF sensor contamination, intake manifold gasket leaks, and a faulty PCV system.
How do I fix P0171 cheaply on a Sierra?
Clean the MAF first with CRC MAF cleaner ($10, fixes ~30% of cases). If that doesn’t help, inspect the PCV valve and hose for cracks. Only escalate to intake gaskets or a new MAF after those steps.
Will P0171 cause P0420 on my Sierra?
Yes, eventually. Extended lean operation overheats the catalyst. Once that damage is done, you’ll see P0420 appear and need cat replacement. Fix the lean condition early to avoid the cascade.
Can a bad O2 sensor cause P0171?
In theory yes, but on Sierras it’s far less common than MAF contamination or intake leaks. Replace O2 sensors only after the intake and MAF are ruled out.