Most Common Buick Check Engine Codes (Enclave, LaCrosse, Regal, Encore, and LeSabre)

Understanding Buick Check Engine Codes

Buick is General Motors' near-luxury brand, sharing platforms and powertrains with Chevrolet, GMC, and Cadillac. The Enclave uses GM's 3.6L V6 shared with the Chevrolet Traverse and GMC Acadia. The Encore uses the 1.4L turbocharged Ecotec four-cylinder. The Encore GX, a separate/larger model, uses a 1.2L or 1.3L turbocharged three-cylinder -- no 1.4L four-cylinder option. The LaCrosse and Regal use either the 2.4L Ecotec or the 3.6L V6. Older Buick models like the LeSabre, Park Avenue, and Century are powered by the legendary 3800 Series II V6 -- one of GM's most durable engines but with a well-known intake manifold gasket weakness. Because Buick shares components across the GM family, most check engine codes and their fixes are identical to those on Chevrolet and GMC models. Buick-branded replacement parts from dealers carry a slight premium, but aftermarket parts from ACDelco are identical in quality and widely available.

P0171 -- System Too Lean (Bank 1)

P0171 on Buick vehicles indicates a lean fuel condition on Bank 1. On the LeSabre, Park Avenue, and Century with the 3800 Series II V6, P0171 is the hallmark symptom of the infamous upper intake manifold (UIM) gasket failure. The original plastic UIM gaskets warp and crack over time, allowing coolant to leak into the intake ports and unmetered air to enter the engine. This is one of the most well-known GM issues and affects nearly every 3800 Series II engine between 80,000 and 150,000 miles. The repair costs $300-$600 at a shop and uses an updated gasket design that resolves the issue permanently. On the Enclave with the 3.6L V6, P0171 is more commonly caused by a dirty mass airflow sensor ($40-$80) or a cracked PCV hose. On the Encore with the 1.4L turbo, check for boost leaks at the intercooler pipe connections.

P0174 -- System Too Lean (Bank 2)

P0174 appearing alongside P0171 on a Buick with the 3800 Series II V6 confirms the upper intake manifold gasket failure, since the leak affects both banks simultaneously. When only P0174 appears alone on a V6 Buick, check for a vacuum leak on the Bank 2 side of the engine, typically a cracked vacuum line or a leaking brake booster hose. On the Enclave and LaCrosse with the 3.6L V6, P0174 by itself can indicate a failing Bank 2 oxygen sensor ($40-$70) that is reading incorrectly and causing the ECU to over-lean the fuel mixture. On the Regal with the 2.0L turbo Ecotec, P0174 is not applicable since this is an inline four-cylinder engine with only one bank.

P0300 -- Random/Multiple Cylinder Misfire Detected

P0300 on the 3800 Series II V6 in the LeSabre and Century is frequently caused by the intake manifold gasket leak allowing coolant into the combustion chambers. If coolant is leaking past the gasket, you may notice white smoke from the exhaust and a sweet coolant smell. Fix the intake gasket first before chasing ignition components. On the Enclave with the 3.6L V6 (2008-2013), P0300 alongside P0008 or P0016 points to the timing chain stretch issue that affects early 3.6L engines. The timing chain replacement costs $1,500-$2,500. GM phased in an improved chain design starting around 2013-2015, significantly reducing (but not eliminating) the failure rate; on those later Enclave models, P0300 is more likely ignition-related -- spark plugs ($8-$15 each, iridium, 100K-mile interval) or ignition coils ($25-$45 each). On the Encore with the 1.4L turbo, carbon buildup on the intake valves due to direct injection is a known cause of misfires after 60,000 miles.

P0420 -- Catalyst System Efficiency Below Threshold (Bank 1)

P0420 on Buick vehicles generally appears between 100,000 and 150,000 miles. On the 3800 Series II V6, a failed intake manifold gasket that has been leaking coolant into the cylinders for an extended period can contaminate and destroy the catalytic converter, so always fix the intake gasket issue before addressing P0420. A catalytic converter for the 3800 costs $200-$400 aftermarket. On the Enclave with the 3.6L V6, the converter is more expensive ($400-$800 aftermarket) and can be contaminated by oil consumption from worn valve seals. Before replacing any catalytic converter, test the downstream oxygen sensor ($40-$70) -- a sluggish sensor is a cheaper and simpler fix that can resolve P0420.

P0442 -- EVAP System Small Leak Detected

P0442 indicates a small leak in the evaporative emissions system. On the LeSabre and Park Avenue, the EVAP system hoses running along the underside of the vehicle become brittle with age and develop small cracks at connection points. Inspect all rubber hoses between the fuel tank, charcoal canister, and purge valve for cracks. On the Enclave, the gas cap seal is the most common culprit -- replace the cap ($12-$18) and clear the code before pursuing further diagnosis. On the Encore, the EVAP purge solenoid can develop a hairline crack in its housing, causing a small leak that is difficult to detect without a smoke test ($80-$150 at a shop). P0442 does not affect drivability and is not an urgent repair.

P0446 -- EVAP Vent System Control Circuit

P0446 on Buick models indicates a problem with the EVAP vent valve circuit. The vent valve is typically located near the charcoal canister at the rear of the vehicle. On the LeSabre and older Buick models, road debris and rust can damage the vent valve or its wiring harness, especially in northern states with road salt. The vent valve costs $30-$50 and is straightforward to replace. On the Enclave and LaCrosse, check the wiring connector at the vent valve for corrosion before replacing the valve itself -- cleaning the connector with electrical contact cleaner can resolve the code without parts replacement. On all GM vehicles, a spider web or insect nest inside the vent valve can cause blockage and trigger this code.

P0449 -- EVAP Vent Solenoid Control Circuit

P0449 is one of the most common codes on GM vehicles including Buick and indicates an electrical problem with the EVAP vent solenoid. This solenoid is located near the charcoal canister, typically at the rear of the vehicle near the fuel tank. The solenoid costs $20-$40 and is a simple replacement. On the Enclave, the solenoid is accessible from underneath the rear of the vehicle. On older Buick models like the LeSabre, corrosion on the electrical connector is more common than actual solenoid failure. Symptoms are minimal -- you may notice a slight fuel smell or difficulty at the gas pump with the nozzle clicking off prematurely. This code will cause an emissions test failure but has no effect on drivability.

P0496 -- EVAP System High Purge Flow

P0496 means the EVAP purge solenoid is stuck open, allowing fuel vapors to flow into the intake manifold continuously rather than only when commanded by the ECU. This is extremely common across all GM vehicles including Buick. The purge solenoid is located on or near the intake manifold and costs $25-$40 for an aftermarket replacement. On the Enclave and LaCrosse, the purge valve is easily accessible on top of the engine. On the LeSabre with the 3800 V6, the purge valve is located on the intake plenum. Symptoms include rough idle when cold, difficulty filling the gas tank, and occasional stalling. The replacement is a 15-minute DIY job requiring only basic hand tools.

P0507 -- Idle Air Control System RPM Higher Than Expected

P0507 indicates the idle speed is higher than the ECU's target, typically above 800-900 RPM. On the LeSabre and Century with the 3800 Series II V6, a vacuum leak from the failed upper intake manifold gasket is the most common cause. Fix the intake gasket first, as the unmetered air entering the engine causes elevated idle speed. On the Enclave and LaCrosse, a dirty throttle body is the most common cause -- carbon buildup on the throttle plate prevents it from closing fully. Clean the throttle body with throttle body cleaner ($6-$10) and reset the idle learn procedure by disconnecting the battery for 15 minutes. On the Encore with the 1.4L turbo, a sticking PCV valve or a boost leak can cause elevated idle.

P0700 -- Transmission Control System Malfunction

P0700 is a generic flag indicating the transmission control module has stored its own fault code. On the Enclave with the 6T75 six-speed automatic, common underlying issues include torque converter shudder, harsh 3-4 shifting, and solenoid failures. The 6T75 is the same transmission used in the Chevrolet Traverse and GMC Acadia. On the 2010-2011 LaCrosse and 2011 Regal with the 6T40/6T45 transmission, a known wave plate failure can cause P0700 alongside harsh engagement. On the LeSabre with the 4T65-E transmission, the pressure control solenoid is a common failure point that causes harsh shifts and P0700. For any P0700 code, a scanner with enhanced GM transmission diagnostics is needed to read the specific transmission fault code stored in the TCM.

Buick Model-Specific Issues

The LeSabre (2000-2005) and Park Avenue are anchored by the 3800 Series II V6, which is one of GM's most durable engines. The intake manifold gasket is the primary weakness, but once repaired with the updated gasket design, these engines routinely exceed 250,000 miles. The Enclave (2008-present) shares its platform with the Chevrolet Traverse and GMC Acadia. The 2008-2013 models with the 3.6L V6 are prone to timing chain stretch; 2014+ models have an updated chain design. The LaCrosse (2010-2019) is generally reliable with either the 2.4L or 3.6L engine. The Regal (2011-2017) with the 2.0L turbo offers strong performance but can develop turbocharger wastegate issues around 80,000-100,000 miles. The Encore (2013-present) with the 1.4L turbo Ecotec is generally reliable but can develop PCV system issues and intake valve carbon buildup due to direct injection.

DIY Tips for Buick Owners

Buick vehicles are among the most DIY-friendly in the GM lineup. The 3800 Series II V6 in the LeSabre and Park Avenue is one of the easiest engines to work on, with excellent access to all components in the transverse-mounted engine bay. The Enclave has a tighter engine bay with the 3.6L V6, but most sensors and ignition components are still accessible. For OBD-II scanning, any standard scanner reads Buick powertrain codes, but a GM-compatible scanner like the Autel MaxiSys or a Bluetooth adapter with the Torque Pro app provides access to transmission and body module codes. ACDelco parts are the best value for GM vehicles -- they are manufactured to OEM specifications at significantly lower prices than dealer parts. For the 3800 intake manifold gasket repair, Dorman offers a complete kit with updated gaskets and bolts for around $50-$80. Join buickforums.com for model-specific advice and DIY walkthroughs.

Frequently Asked Questions