Most Common GMC Check Engine Codes (Sierra, Terrain, Acadia)

GMC Check Engine Codes Overview

GMC vehicles share their powertrains with Chevrolet, so the same engine codes and failure patterns apply across both brands. The GMC Sierra uses the same 5.3L and 6.2L V8 engines found in the Chevy Silverado, the first-generation Terrain (2010-2017) shares its Ecotec 2.4L (and 3.0L/3.6L V6 options) with the Chevy Equinox of that era, while the 1.5L turbo (shared with Equinox) applies only to the second-generation Terrain, 2018-present, and the Acadia uses the same 3.6L V6 as the Chevy Traverse. The 5.3L V8 is the most common Sierra engine and has well-documented Active Fuel Management (AFM) lifter problems that mirror the Hemi MDS issues. The Ecotec 2.4L in the 2010-2017 Terrain has a known timing chain defect that can cause engine damage. Knowing which codes are routine maintenance items versus signs of a serious mechanical problem helps you prioritize repairs and avoid costly engine damage.

P0300 -- Random/Multiple Cylinder Misfire (AFM Lifter Failure)

P0300 on the 5.3L V8 (found in the 2007-2023 Sierra 1500) is frequently caused by Active Fuel Management (AFM) lifter failure. AFM deactivates four cylinders under light load to improve fuel economy, but the specialized AFM lifters are a major reliability weak point. A failed AFM lifter causes a misfire on the affected cylinder, and you will typically see P0300 alongside a specific cylinder code like P0306 or P0308. GM issued TSB 15-06-01-002F addressing AFM lifter failures (DTC P0300, covers 5.3L L83/6.2L L86/LT1/LT4) and has released updated lifter designs multiple times. This has not been handled as a formal recall -- GM offers a "Power Component Coverage" extended-warranty letter, and it remains the subject of ongoing, uncertified class-action litigation. The repair involves replacing all lifters and potentially the camshaft if lobe damage occurred, running $2,500-$5,000 at a dealer. GM introduced Dynamic Fuel Management (DFM) on the 2019+ 5.3L, which can shut down any combination of cylinders, and early data suggests DFM lifters are more reliable than the older AFM design. Many Sierra owners choose to install an AFM disabler device ($200-$400) that keeps all eight cylinders firing at all times, which can prevent future lifter failures but does not fix one that has already collapsed. On the Terrain 2.4L Ecotec, P0300 is more commonly caused by timing chain stretch, covered in detail below.

P0446 -- EVAP Vent System Performance

P0446 indicates a problem with the EVAP vent valve circuit, and it is one of the most common codes on GMC trucks and SUVs. On the 2007-2013 Sierra and Yukon, the EVAP vent solenoid is mounted near the charcoal canister at the rear of the vehicle, and it is exposed to road spray, mud, and salt. The solenoid corrodes or its filter clogs, preventing the EVAP system from venting properly. The vent solenoid costs $25-$50 and takes about 30 minutes to replace. On the 2010-2017 Terrain, the EVAP vent valve is in a similar location and suffers from the same exposure issues. GM issued TSB 14-CE-0040 for EVAP system codes on multiple GMT900 platform trucks (2007-2014 Sierra, Yukon, Tahoe, Suburban). If replacing the vent solenoid does not fix P0446, check the EVAP canister itself for saturation or clogging ($80-$150 for the part). On the 2014-2018 Sierra with the updated K2XX platform, the EVAP system is more robust, but the purge valve on the engine ($30-$60) becomes the more common failure point.

P0420 and P0171 -- Catalytic Converter and Lean Codes

P0420 (Catalyst System Efficiency Below Threshold) on the Sierra 5.3L typically appears after 120,000-150,000 miles. The truck uses two catalytic converters, and replacement costs $500-$1,500 per side for OEM-quality parts. Before replacing the converter, check for exhaust leaks at the exhaust manifold bolts -- the 5.3L is known for broken exhaust manifold bolts, especially on the driver side. A broken bolt creates an exhaust leak that introduces oxygen into the exhaust stream and gives a false P0420 reading. P0171 (System Too Lean Bank 1) on the 5.3L V8 is most commonly caused by a cracked intake manifold gasket or a failing fuel pressure regulator. On the 2007-2013 Sierra 5.3L with the plastic intake manifold, the gaskets deteriorate and create vacuum leaks. The gasket set costs $30-$60, but the labor is significant because the intake manifold must be removed. On the Terrain 2.4L, P0171 is often caused by a cracked PCV hose or a dirty MAF sensor. On the Acadia 3.6L, P0171 can indicate timing chain stretch causing cam timing to drift out of specification.

P0325 and P0131 -- Knock Sensor and O2 Sensor Codes

P0325 (Knock Sensor Circuit Malfunction) is a well-known issue on the 5.3L V8, particularly on 2007-2013 Sierra trucks. The knock sensors are mounted under the intake manifold and are exposed to coolant contamination from the intake gaskets. When coolant seeps onto the knock sensor connector, it corrodes the terminals and triggers P0325. The fix involves replacing the knock sensors ($20-$40 each, two required), the wiring harness ($40-$80), and usually the intake manifold gaskets while you are in there. The total job runs $400-$800 at a shop due to the labor involved in removing the intake manifold. GM issued a revised knock sensor harness (part number 12601822) with improved sealing. P0131 (O2 Sensor Circuit Low Voltage Bank 1 Sensor 1) on the Sierra indicates the upstream oxygen sensor is reading lean or has an electrical fault. The sensor itself costs $40-$80, but before replacing it, inspect the wiring connector for heat damage -- the driver-side upstream O2 sensor wiring on the 5.3L runs close to the exhaust manifold and can melt. On the Terrain 2.4L, P0131 is sometimes triggered by oil contamination of the sensor from excessive PCV system oil vapor.

Terrain 2.4L Ecotec Timing Chain Issues

The 2010-2017 GMC Terrain with the 2.4L Ecotec engine has a well-documented timing chain defect that deserves special attention. The timing chain, tensioner, and guides wear prematurely, sometimes as early as 60,000-80,000 miles. As the chain stretches, it retards cam timing and triggers codes including P0300 (misfire), P0011 (intake cam over-advanced), P0016 (crankshaft/camshaft correlation), and P0017. A rattling noise on cold startup that fades after a few seconds is the early warning sign. If you ignore it, the chain can skip teeth and cause the pistons to contact the valves, destroying the engine. The repair involves replacing the timing chain, tensioner, guides, and both VVT solenoids, costing $1,200-$2,200 at a shop. This engine has also been the subject of class-action litigation (Berman v. General Motors, covering MY2010-2013 2.4L Ecotec oil-consumption/piston-assembly claims) -- check with an attorney or GM directly on current eligibility rather than assuming a specific settlement applies to your VIN. If your Terrain has over 80,000 miles and you hear any chain rattle on startup, get it inspected immediately -- catching it early saves the engine.

Frequently Asked Questions