P0442 on 2010-2017 GMC Terrain: EVAP Small Leak Causes and Fixes

What's Unique About the 2010-2017 Gmc TERRAIN

On the GMC Terrain and its sibling, the Chevy Equinox, the P0442 code is a very common issue. While the gas cap is a frequent cause on many vehicles, these GM models are particularly known for issues with the purge and vent valves. GM has issued technical service bulletin 21-NA-124, which guides technicians on diagnosing these EVAP leaks and suggests a specific order of operations: check lines, then the vent valve, then the purge valve. GM has also released TSB #PIT4943D, which directs technicians to a specific Techlink article on using an evaporative emissions system tester for diagnostics. Owners on forums like terrainforum.net often find that replacing the purge valve (located on the engine) resolves the code, especially if it's accompanied by a P0496. In regions with heavy road salt use, the metal EVAP lines running along the vehicle's underbody are also a known failure point due to rust perforation.

Diagnostic Flowchart

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

Generation note: The 2010-2017 year range covers the first generation of the GMC Terrain. While engine options (2.4L I4, 3.0L V6, 3.6L V6) exist, the causes and diagnostic procedures for P0442 are broadly similar across the generation as they share the same fundamental EVAP system design.

Symptoms You May Notice

• Check Engine Light is on
• A faint smell of fuel, particularly around the gas cap or rear of the vehicle.
• Vehicle will automatically fail an emissions inspection.
• In some cases, difficulty starting immediately after refueling, which can be caused by a stuck-open purge valve flooding the intake with vapor.

Most Likely Causes

1. Loose or Faulty Gas Cap 🔴 High Probability → Shop Fuel Tank Cap The gas cap is the most frequently handled part of the EVAP system. Its seal can wear out, crack, or simply not be tightened correctly after refueling, making it the most common cause for a small leak code. It is always recommended to use an OEM replacement cap for the best fit and seal.
   How to confirm: First, ensure the gas cap is tightened until it clicks several times. Inspect the rubber O-ring on the cap for cracks, stiffness, or damage. Check the fuel filler neck for rust or debris that could prevent a good seal. If the cap looks worn, replacement is an inexpensive and easy first step.
   Typical fix: Tighten the gas cap. If that doesn't work, replace the gas cap with a new OEM part (e.g., ACDelco GT295) for the best fit.
   Est. part cost: $15-$35
2. Faulty EVAP Purge Valve (Solenoid) 🟡 Medium Probability → Shop Vapor Canister The purge valve is a very common failure point on this GM platform. It can get stuck slightly open, creating a small, persistent leak that the system detects. This issue is so frequent that many owners on forums report going straight to this part after checking the gas cap. A stuck-open purge valve is also the primary cause of a P0496 code.
   How to confirm: With the engine off, disconnect the vapor line from the purge valve and try to blow through it. If any air passes through, the valve is stuck open and must be replaced. A mechanic can also command the valve open and closed with a scan tool while monitoring system pressure to confirm failure.
   Typical fix: Replace the EVAP purge valve. This is typically a straightforward 10-minute DIY job 🎬 Watch: Step-by-step guide to replacing the EVAP purge valve. located on top of the engine.
   Est. part cost: $25-$60
3. Faulty EVAP Vent Valve (Solenoid) 🟡 Medium Probability → Shop Vapor Canister Vent Valve The vent valve, located near the charcoal canister by the fuel tank, can fail to close completely due to dirt, debris, or internal failure, causing a leak. Its location under the vehicle exposes it to road grime and moisture, leading to corrosion and malfunction over time.
   How to confirm: The valve is normally open and should close when 12 volts are applied. A smoke test is the most effective way to confirm if this valve or the surrounding area is leaking. TSB 21-NA-124 suggests checking the vent valve for a stuck-open position after inspecting the EVAP lines.
   Typical fix: Replace the EVAP vent valve. Accessing it requires safely raising the rear of the vehicle. 🎬 See how to access and replace the vent solenoid.
   Est. part cost: $30-$70
4. Cracked or Rusted EVAP Hose/Line ⚪ Low Probability Over time, the plastic and rubber hoses in the EVAP system can become brittle and crack. On the Terrain and Equinox, particularly in the rust belt, the metal sections of the EVAP lines that run along the chassis are known to corrode and develop pinhole leaks, which can be very difficult to spot visually.
   How to confirm: A visual inspection may reveal an obvious crack or disconnected line. However, small cracks and rust perforations are often invisible to the naked eye. A professional smoke test is the definitive method, where smoke is injected into the EVAP system, and any leaks will be visible as smoke escapes.
   Typical fix: Replace the damaged section of hose or the entire rusted line assembly.
   Est. part cost: $10-$160

Rare But Worth Checking

• Cracked Charcoal Canister: → Shop Vapor Canister The charcoal canister itself can develop a hairline crack, causing a small leak. This is less common than valve failure but should be inspected during a smoke test, especially if the vehicle has significant underbody rust.
• Leaking Fuel Tank Pressure Sensor: → Shop Fuel Tank The sensor that monitors pressure in the system can develop a leak through its own seal or housing. This is an uncommon failure but can be identified with a smoke test.

Diagnosis Steps

1. Check the gas cap. Remove it, inspect the seal for cracks or damage, and retighten it until it clicks at least three times. Clear the code and drive for a few days to see if it returns.
2. If the code returns, consider replacing the gas cap with an OEM part as a low-cost, high-probability fix.
3. Check for other codes. If a P0496 is also present, the purge valve is the most likely culprit.
4. Visually inspect the EVAP purge valve in the engine bay and the hoses connected to it for any obvious cracks or damage.
5. Perform a functional test on the purge valve. With the engine off, disconnect the valve's lines and try to blow through it; if air passes, it's faulty and needs replacement.
6. Follow the diagnostic order from GM TSB 21-NA-124: Visually inspect all EVAP lines under the vehicle for secure connections, cracks, or rust.
7. Next, inspect and test the EVAP vent valve near the charcoal canister under the vehicle for damage or being stuck open.
8. If the simple checks do not reveal the issue, the most effective next step is a professional smoke test. This test will pressurize the system with smoke and quickly reveal the location of any small, hard-to-see leaks 🎬 Watch: How to perform a smoke test to find leaks. from hoses, the canister, or the tank itself.

Parts You'll Likely Need

• Fuel Tank Cap (OEM #ACDelco GT295) — This is the most common and easiest fix. The seal wears out over time. Using an OEM cap is highly recommended for a proper seal.
  Trusted brands: ACDelco (OEM), Gates
  OEM price range: $20-$35
  Aftermarket price range: $15-$25
• Vapor Canister Purge Valve / Solenoid (OEM #12690512 (supersedes 12610560)) — A very common failure point on this platform. It gets stuck open, causing a constant small leak and often a P0496 code.
  Trusted brands: ACDelco (OEM), Dorman (911-082), SKP
  OEM price range: $40-$60
  Aftermarket price range: $25-$45
• Vapor Canister Vent Valve / Solenoid (OEM #ACDelco 214-2149 / GM 13575702) — Fails by getting stuck open or not sealing correctly due to debris, causing a leak. Its location under the car makes it prone to corrosion.
  Trusted brands: ACDelco (OEM), Dorman (911-060)
  OEM price range: $50-$80
  Aftermarket price range: $30-$60

Related Codes That Often Appear With This One

• P0455 — P0455 indicates a large EVAP leak. If a component fails significantly (like a valve sticking wide open or a hose completely disconnecting), you might see this code instead of, or along with, P0442. TSB 21-NA-124 covers diagnostics for both codes.
• P0496 — P0496 indicates 'EVAP Flow During a Non-Purge Condition,' which almost always points directly to a faulty purge valve that is stuck open, allowing fuel vapors into the engine at the wrong time. Many owners report fixing P0496 and P0442 simultaneously by replacing the purge valve.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-124: Provides diagnostic tips for finding EVAP leaks related to DTCs P0442 and P0455. It advises a specific diagnostic order: 1. Inspect all EVAP lines for proper seating and damage. 2. Investigate the vent valve for a stuck-open malfunction. 3. Investigate the purge valve for malfunction.
• PIT4943D: Directs technicians to use an EVAP system tester (smoke machine) for diagnosing code P0442, reinforcing that visual inspection alone is often insufficient.

Platform-Specific Known Issues

• Purge Valve is a Very Common Culprit: → Shop Vapor Canister Numerous owners on forums for the Terrain and its platform-mate, the Chevy Equinox, report that the P0442 code was ultimately caused by a failed purge valve (solenoid) on the engine, often after first replacing the gas cap with no success. It is often accompanied by code P0496.
• Rusted EVAP Lines in Salt-Belt Regions: For vehicles operated in areas where road salt is used in winter, the metal EVAP lines running along the underbody are susceptible to corrosion. This can cause pinhole leaks that are difficult to see without a smoke test.

Mechanic-Grade Diagnostic Values

• EVAP Purge Valve Solenoid Resistance — expected: 20-21 Ohms. Failure: A reading significantly higher or lower than the expected range, or an open circuit (infinite resistance), indicates a failed solenoid coil.
• EVAP Vent Valve Solenoid Control Circuit Voltage (Key On, Command OFF) — expected: ~12 Volts (Battery Voltage). Failure: Reading 0 volts when the circuit should be powered indicates an open circuit, a blown fuse, or a wiring issue before the solenoid.

Scan Tool Commands That Help

• GDS2 / Professional Scan Tool: EVAP Purge/Seal Test — This is a primary diagnostic function used to verify a P0442. With the engine running, a technician commands the vent valve to seal the system. If the fuel tank pressure sensor does not show a vacuum being pulled, it suggests the purge valve is not opening. If it shows a vacuum being pulled with the purge command off, it confirms the purge valve is stuck open, a common cause of P0442 and P0496.
• GDS2 / Professional Scan Tool: EVAP Vent Solenoid Command (On/Off) — Used during a smoke test to seal the EVAP system. The vent valve is normally open, so it must be commanded closed to allow the system to build pressure during the test. If the system won't seal, and smoke is seen exiting the vent valve area even when commanded closed, the vent valve is faulty.

Wiring & Ground Locations

• EVAP Purge Solenoid Valve — On the 2.4L engine, it is located on the top rear of the engine. On the 3.6L V6, it is on the right cylinder head.. This is a primary failure point. Knowing its exact location based on the engine is critical for inspection and replacement.
• EVAP Vent Solenoid Valve — Located under the vehicle, near the charcoal canister, which is typically on the driver's side just ahead of the rear wheel, beside the muffler.. This component is exposed to road debris and corrosion, making it a common failure point. Its location is needed for inspection and smoke testing.
• G109 / G112 (2.4L Engine) — G109 is on the top right rear of the engine. G112 is on the lower left front of the engine.. These are primary engine grounds. A poor ground connection can cause erratic behavior or failure of sensors and solenoids, including those in the EVAP system.
• G101 (V6 Engine) — Located on the left front of the engine compartment.. This is a key ground point in the engine bay. A corroded or loose G101 could potentially affect the EVAP purge solenoid's operation.

Real Owner Repair Stories

• YouTube user Kenny's tool review (2017 GMC Terrain) — P0442 (EVAP small leak)
  ❌ Tried (didn't work) The technician immediately suspected the purge valve based on experience.
  ✅ What actually fixed it The EVAP purge valve was stuck open. This was confirmed using a scan tool's 'Purge/Seal' function. With the engine running and the system commanded to seal (purge off, vent closed), the fuel tank pressure sensor immediately showed a vacuum being pulled, proving the purge valve was leaking from the engine intake. Replacing the purge valve fixed the issue.

"I Checked Everything" — The Actual Cause

• In a diagnostic video for a P0442 code where a smoke test did not reveal any external leaks, the technician determined the purge valve was the fault. Even though the valve was not leaking smoke externally, it was intermittently failing to seal properly against engine vacuum, causing the small leak detected by the ECM. The final fix was replacing the purge valve.

OEM Part Supersession History

• 25949889 → 13575702 — This is the part number for the EVAP Vent Valve Solenoid. The new part number is the current replacement for the original.
  Heads up: No incompatibility noted; this is a direct replacement.

Model Year Variations Within This Range

• 2010-2017: The location of the EVAP Purge Valve differs between the 4-cylinder and V6 engines. On the 2.4L I4, it is on the top rear of the engine. On the 3.0L/3.6L V6, it is mounted on the right-side cylinder head. While functionally the same, this affects access for testing and replacement.