P0171 on GMC
System Too Lean (Bank 1)
P0171 on GMC vehicles indicates system too lean (bank 1). Au7o has documented this code across 8 GMC models — most commonly on C/K 1500, Safari, Sierra 1500. This code means the engine's computer has detected that the air-fuel mixture on Bank 1 (the side of the engine with cylinder #1) is running too lean — meaning there is too much air relative to fuel. The computer watches the oxygen sensors and has had to add a large amount of extra fuel (long-term fuel trim) to try to compensate, but it has hit its correction limit. A lean condition can cause rough idle, hesitation, reduced power, and over time can run the engine hotter than normal. It usually points to either unmetered air leaking into the engine or not enough fuel being delivered. Typical repair costs on GMC range from $200 to $6,500, depending on the specific model and root cause.
Common Causes of P0171
- •Vacuum or intake air leak (cracked hose, gasket, or PCV system)
- •Dirty or failing mass airflow (MAF) sensor
- •Weak fuel pump or restricted fuel filter
- •Clogged or dirty fuel injectors
- •Faulty or aged upstream oxygen sensor
- •Leaking intake manifold gasket
- •Low fuel pressure or failing fuel pressure regulator
- •Exhaust leak ahead of the oxygen sensor
P0171 on GMC by Model
GMC C/K 1500(1 issue)
- 5.7L Vortec Spider Injector Assembly Failure1996-1998
Same CPI spider injector issue as Chevrolet C/K. The 5.7L Vortec V8 spider assembly poppet nozzles clog and fuel lines crack.
GMC Safari(2 issues)
- 4.3L Central Port Injection (CPI) Spider Injector Failure1996-2005
The 4.3L Vortec in the Safari uses a central port injection system ('spider injector') that develops poppet valve sticking and fuel line cracks. This causes hard starting, rough idle, and a strong fuel smell from leaking fuel inside the intake manifold.
- 4.3L V6 Intake Manifold Gasket Leak1996-2005
Same intake gasket issue as the Astro van. The under-dash engine location makes this a more labor-intensive repair.
GMC Sierra 1500(2 issues)
- Direct Injection Carbon Buildup on Intake Valves2014-2023
Direct injection engines do not spray fuel over the intake valves like port injection systems, allowing carbon deposits from oil and blow-by gases via the PCV system to accumulate on intake valve backs and ports. Over time, this buildup restricts airflow causing performance and efficiency loss. The 5.3L and 6.2L engines with direct injection are susceptible to this issue typically after 60,000-100,000 miles.
- Fuel Pump Module Failure Causing No-Start or Stalling2000-2007
A common GMT800 Sierra problem is failure of the in-tank fuel pump module, often from worn pump motors or failed level-sender/module electronics. Owners report long crank, hard starting, loss of power under load, or sudden stall/no-start conditions, especially as mileage climbs. This issue is widely documented in owner forums and complaint databases across 4.3L, 4.8L, 5.3L, and 6.0L trucks.
GMC Sierra 2500HD(1 issue)
- LML Duramax EGR Cooler and EGR Valve Failure2011-2016
The LML Duramax EGR (exhaust gas recirculation) cooler is prone to coolant leaks internally, allowing coolant to enter the intake manifold and combustion chambers. Coolant in the intake causes white smoke, rough running, and potential hydrolocking of cylinders. The EGR valve also sticks open or closed from carbon buildup, causing rough idle, black smoke, and check engine lights. The EGR cooler failure can occur as early as 60,000 miles on trucks used in stop-and-go driving. GM issued multiple TSBs addressing EGR cooler design improvements.
GMC Sonoma(1 issue)
- 4.3L V6 Intake Manifold Gasket Leak1996-2004
Same intake gasket issue as the S-10 platform. The 4.3L Vortec V6 intake gaskets fail from heat cycling.
GMC Suburban(1 issue)
- 5.7L Vortec Intake Manifold Gasket and CPI Issues1996-1999
The GMC Suburban shares the same 5.7L Vortec intake gasket and spider injector issues as the C/K 1500. The larger vehicle runs hotter, which can accelerate gasket degradation.
GMC Terrain(1 issue)
- 2.4L I4 Excessive Oil Consumption and Piston Ring Failure2010-2017
The 2.4L LEA and LE9 four-cylinder engines in 2010-2017 Terrain are among the most reported excessive oil consumption issues in GM's lineup. Many owners consume 1 quart of oil every 1,000-2,000 miles. The root cause is inadequate piston ring tension combined with piston ring land fractures that allow oil to bypass rings into the combustion chamber. The problem was subject to class action lawsuits and GM Customer Satisfaction Programs. Burned oil causes spark plug fouling, catalytic converter damage, and oil pressure warnings. This is the same issue affecting the Chevy Equinox with the same engine.
GMC Yukon XL(2 issues)
- Cracked Exhaust Manifold Bolts / Manifold Leak (5.3L/6.2L V8) Causing Cold-Start Tick2007-2020
Yukon XL V8 engines (notably 5.3L and 6.2L) can develop broken exhaust manifold bolts and/or warped manifolds, leading to an exhaust leak that is loudest on cold start. Owners describe a ticking sound that diminishes as the engine warms and the manifold expands. This is a well-documented GM truck/SUV issue in owner reports and service discussions for these engines.
- Fuel Pump Module Failure Leading to No-Start or Intermittent Stalling2000-2006
In-tank fuel pump module failure is a common GMT800 problem, especially as mileage climbs or when vehicles are frequently run near empty. Owners report extended cranking, hard starts after sitting, sudden stalling, loss of power under load, or complete no-start conditions. The issue is well represented in owner reports and repair histories across 5.3L, 6.0L, and 8.1L applications.
Looking for P0171 on a different make?
View P0171 across all makes →Frequently Asked Questions
What does P0171 mean on GMC?▼
P0171 stands for "System Too Lean (Bank 1)." This code means the engine's computer has detected that the air-fuel mixture on Bank 1 (the side of the engine with cylinder #1) is running too lean — meaning there is too much air relative to fuel. The computer watches the oxygen sensors and has had to add a large amount of extra fuel (long-term fuel trim) to try to compensate, but it has hit its correction limit. A lean condition can cause rough idle, hesitation, reduced power, and over time can run the engine hotter than normal. It usually points to either unmetered air leaking into the engine or not enough fuel being delivered. On GMC specifically, this code is documented across 8 models.
What causes P0171 on GMC vehicles?▼
Common causes on GMC: Vacuum or intake air leak (cracked hose, gasket, or PCV system), Dirty or failing mass airflow (MAF) sensor, Weak fuel pump or restricted fuel filter, Clogged or dirty fuel injectors, Faulty or aged upstream oxygen sensor. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0171 on a GMC?▼
Repair costs on GMC range from $200 to $6,500, depending on the specific model and root cause.
Which GMC models have P0171 documented?▼
Au7o has documented P0171 on 8 GMC models: C/K 1500, Safari, Sierra 1500, Sierra 2500HD, Sonoma, Suburban, Terrain, Yukon XL.