P0442 on 2016-2023 Buick Envision: EVAP Small Leak Causes and Fixes

What's Unique About the 2016-2023 Buick ENVISION

For modern GM vehicles like the Buick Envision and its platform mates (Chevy Equinox, GMC Terrain), the diagnostic approach for EVAP leaks is well-defined. Manufacturer service bulletin #21-NA-124 directly addresses P0442 and P0455, emphasizing a systematic check starting with EVAP line connections before moving to valve testing. The purge valve is a particularly common failure point across this platform, often triggering a P0496 code 🎬 Watch: How to replace the purge valve on this platform. alongside the P0442.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Generation note: The 2016-2023 Buick Envision covers two generations: the first (2016-2020) which uses a traditional gas cap, and the second (2021-2023) which may have a capless fuel filler system. For 2016-2020 models, a faulty gas cap is a primary suspect. For 2021+ models, the focus shifts more immediately to the purge and vent valves. Part numbers for components like the EVAP purge valve may also differ. Always verify the part number for your specific model year before purchasing.

Symptoms You May Notice

• Check Engine Light is on.
• A faint fuel smell, particularly around the rear of the vehicle.
• In rare cases, difficulty starting or a long crank time immediately after refueling if the purge valve is stuck open.
• A buzzing sound from the vehicle after it has been parked, which can be the EVAP system performing a self-test.

Most Likely Causes

1. Loose or Faulty Gas Cap (2016-2020 Models) 🔴 High Probability → Shop Fuel Tank Cap The gas cap is the most frequently removed and re-installed component of the emissions system. The rubber O-ring seal can wear out, crack, or get dirty over time, preventing a proper seal. Using non-OEM caps is also a common source of failure.
   How to confirm: First, ensure the cap is tightened until it clicks at least once. Inspect the rubber seal on the cap for cracks, stiffness, or debris. Also inspect the fuel filler neck for rust or dirt that could prevent a seal. If the seal is damaged or you have an aftermarket cap, it's the first part to replace.
   Typical fix: Clean the cap and filler neck sealing surfaces. If the cap is damaged or the light returns, replace the gas cap with a new OEM part, such as ACDelco GT330 (GM #13519643). Aftermarket caps are not recommended as they frequently cause leak codes.
   Est. part cost: $20-$35
2. Faulty EVAP Purge Valve (Purge Solenoid) 🟡 Medium Probability → Shop Vapor Canister The purge valve is a very common failure point on many GM vehicles, including the Envision and its platform mates, the Equinox and Terrain. It's an electromechanical part that cycles frequently, and it can get stuck slightly open, causing a small leak that the system detects. This is often the primary cause on capless fuel system models.
   How to confirm: The valve is located in the engine bay. A quick test involves removing the valve (while leaving it electrically connected) and trying to blow through it. If air passes through, it's stuck open and faulty. A professional diagnosis involves a scan tool to command the valve closed and a smoke machine to see if smoke passes through it. A P0496 code appearing with P0442 strongly points to this valve.
   Typical fix: Replace the EVAP purge valve. This is often a straightforward DIY job. An example part number for some Envision models is ACDelco 12690512.
   Est. part cost: $30-$70
3. Faulty EVAP Vent Valve (Vent Solenoid) ⚪ Low Probability → Shop Vapor Canister Vent Valve Located near the charcoal canister at the rear of the vehicle, this valve can get stuck or fail to seal completely due to dirt and moisture exposure from under the car. It is a known failure point on GM vehicles, though less common than the purge valve for a small leak code.
   How to confirm: This valve is normally open and closes when the system runs its test. Diagnosis usually requires a scan tool to command it closed and a smoke test to see if it's leaking. It is often replaced after the gas cap and purge valve have been ruled out.
   Typical fix: Replace the vent valve. Access can be more difficult than the purge valve, as it's mounted near the fuel tank, sometimes as part of the charcoal canister assembly.
   Est. part cost: $35-$60
4. Cracked or Disconnected EVAP Hose ⚪ Low Probability The plastic and rubber lines that carry fuel vapor can become brittle with age and exposure to heat and elements, leading to small cracks. In salt-belt regions, the metal EVAP lines running under the vehicle can rust and develop pinhole leaks.
   How to confirm: A thorough visual inspection of all accessible EVAP lines between the engine bay and the fuel tank is the first step. The definitive method is a smoke test, which will cause smoke to pour out of any cracks or loose connections. This was the confirmed fix in a detailed repair video for a platform-mate Chevy Equinox.
   Typical fix: Replace the cracked section of hose or the entire rusted line assembly. A replacement line from GM can cost over $100.
   Est. part cost: $10-$160

Rare But Worth Checking

• Cracked EVAP Charcoal Canister: → Shop Vapor Canister The canister itself can develop a small hairline crack from road debris or age. This is often found during a smoke test after all valves and hoses have been checked. Overfilling the fuel tank can also saturate and damage the canister.
• Leaking Fuel Tank Filler Neck: → Shop Fuel Tank Rust or damage to the metal pipe leading to the gas tank can cause a leak where the gas cap seals. This is more common in areas with heavy road salt use and can be cleaned with a wire brush as a temporary measure, but may require replacement for a permanent fix.
• Leaking Fuel Tank Sending Unit Gasket: → Shop Fuel Tank A user on a GM forum reported this as the ultimate fix after replacing other common parts. A failing gasket on the fuel pump access plate can cause a small leak, often accompanied by a fuel smell. This leak is typically found with a smoke test.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0442 is present.
2. For 2016-2020 models, inspect the gas cap. Remove it, check the seal for damage, and clean any dirt from the cap and filler neck. Reinstall it, ensuring it clicks multiple times. For 2021+ models, inspect the capless filler flap for debris or damage.
3. Clear the code and drive for a few days to see if it returns. A complete EVAP drive cycle may be needed for the light to turn off or come back on. If it does, proceed with further diagnosis.
4. Perform a visual inspection of the EVAP purge valve (in the engine bay) and its hoses for any obvious cracks or disconnections.
5. Test the purge valve. With the engine off, remove the valve and try to blow through it. If air passes, it is stuck open and needs replacement.
6. Visually inspect the vent valve and charcoal canister area underneath the vehicle, near the fuel tank, for any visible damage.
7. For a definitive diagnosis, perform a smoke test. This involves injecting low-pressure smoke into the EVAP system's service port and looking for where the smoke escapes. This will pinpoint the exact location of the leak, whether it's a hose, valve, canister, or gasket.

Parts You'll Likely Need

• Gas Cap (for 2016-2020 models) (OEM #ACDelco GT330 (GM #13519643)) — This is the most common cause due to wear and tear on the seal. It's the cheapest and easiest part to replace first. Always use an OEM cap for best results.
  Trusted brands: ACDelco, GM Genuine Parts
  OEM price range: $20-$35
  Aftermarket price range: $15-$25
• EVAP Vapor Canister Purge Valve / Solenoid (OEM #ACDelco 12690512 (verify for specific year/engine)) — A very common failure point on GM vehicles that causes a small leak when it fails to close completely. Often the cause if P0496 is also present.

Related Codes That Often Appear With This One

• P0455 — Indicates a large EVAP leak. The same faulty component (like a very stuck valve or a completely disconnected hose) can sometimes trigger a P0442 initially and then a P0455, or vice-versa. TSB #21-NA-124 directly links these two codes.
• P0496 — Indicates high purge flow, which is very commonly caused by a purge valve that is stuck open. This is a strong indicator that the purge valve is the specific source of your P0442 leak. This is a frequent combination on GM vehicles.
• P0449 — Indicates a fault in the EVAP vent valve solenoid control circuit. While this points to an electrical issue with the vent valve, it can appear alongside leak codes if the valve is failing mechanically and electrically.

Technical Service Bulletins (TSBs) & Recalls

• TSB #21-NA-124: 'Diagnostic Tip for Malfunction Indicator Lamp (MIL) Illuminated - DTC P0442 and/or P0455 Set' - Provides a diagnostic flowchart for technicians, starting with checking line connections before testing valves.
• TSB #PIT4943D: Directs technicians to review a Techlink article on using an EVAP smoke tester, reinforcing the tool's importance for accurate diagnosis.

Platform-Specific Known Issues

• GM has issued Technical Service Bulletin (TSB) #21-NA-124, which provides diagnostic tips for technicians dealing with P0442 and/or P0455. It emphasizes a systematic check of all purge line connections for proper seating and damage before suspecting a faulty valve.
• An older TSB, #PIT4943D, also points technicians toward specific diagnostic articles for using an EVAP smoke machine, underscoring the importance of this tool for accurate diagnosis.
• Owners of platform-mate vehicles like the Chevy Equinox and GMC Terrain frequently report the purge valve as the fix for P0442, especially when accompanied by a P0496 code or hard starting after refueling.

Hidden / Shadow Codes Worth Checking

• Mode 10 DTC (Permanent DTC): After a repair is made and codes are cleared, the ECM stores a 'permanent' version of the fault code. This code cannot be erased with a standard scan tool 'clear codes' function. (see via An advanced OBD-II scanner with support for Mode $0A (or Mode 10) can display Permanent DTCs. The code is only cleared by the vehicle's computer after it successfully runs the EVAP monitor over several drive cycles (e.g., up to 40 warm-up cycles) without the fault reoccurring.)

Scan Tool Commands That Help

• GDS2 (GM Tech 2 successor): EVAP Service Bay Test — Used to command the ECM to run the entire EVAP leak self-test on demand in the shop, verifying a leak exists or that a repair was successful without a lengthy drive cycle. Note: This test has prerequisites, such as fuel level being between 15-85% and engine coolant temperature being below a certain threshold (e.g., 158°F/70°C).
• GDS2 / Professional Bidirectional Scanner: EVAP Purge/Seal — This function allows a technician to manually command the normally-open Vent Valve to close, sealing the system. This is a critical step before performing a smoke test to ensure the system is a closed loop.
• GDS2 / Professional Bidirectional Scanner: EVAP Purge Solenoid Control — Allows for manually commanding the Purge Valve open and closed. While cycling the valve, a technician can check for an audible click or use a smoke machine to see if it's leaking internally when commanded closed.

Wiring & Ground Locations

• Engine Compartment Fuse Box — Located in the engine bay, this box houses fuses and relays for critical systems, including potentially the EVAP system components' power source.. A blown fuse for the EVAP purge or vent solenoid could cause a circuit code (like P0449) but could also accompany a leak code if the valve is unable to operate correctly to seal the system for a test.
• Main Engine Harness Grounds — On many GM vehicles, critical ECM and sensor grounds are attached to the rear of the cylinder heads or on bellhousing bolts.. A poor ground connection for the ECM or related sensors could potentially cause erratic behavior in the EVAP system components or incorrect readings from the fuel tank pressure sensor, leading to a false code.

Real Owner Repair Stories

• YouTube channel 'Repair Shop' (2012 Chevy Equinox (platform mate to Envision)) — Check Engine Light with code P0442.
  ❌ Tried (didn't work) Replacing the gas cap with an OEM part., Replacing the EVAP purge solenoid.
  ✅ What actually fixed it A smoke test revealed a heavily rusted and leaking metal EVAP line that runs from the charcoal canister to the purge solenoid. Replacing the entire line assembly (~$160 for the part) resolved the code.

"I Checked Everything" — The Actual Cause

• In a diagnostic video on a similar GM vehicle (Chevy Tahoe), a smoke test revealed no external leaks from any hoses, the canister, or the vent valve. The technician concluded that the only remaining possibility was an internally leaking EVAP purge valve, which was not sealing completely but was not leaking externally. Replacing the purge valve fixed the P0442 code.

OEM Part Supersession History

• 12690512 → 12737252 — Standard part evolution and replacement. The new part number is the current service replacement for the old one.
  Heads up: Part number 12690512 was also superseded by 12610560 and 12661763 before the current number 12737252. When ordering, using the latest part number is recommended.

Model Year Variations Within This Range

• 2021-2023: Second generation Envision models (2021+) use a capless fuel filler system. For a P0442 on these models, the gas cap is eliminated as a possible cause, and diagnosis should immediately focus on the purge valve, vent valve, and EVAP lines.