P0455 on 2008-2015 Buick Enclave: EVAP Large Leak Causes and Fixes

What's Unique About the 2008-2015 Buick ENCLAVE

On the first-generation Buick Enclave and its GM Lambda platform siblings (GMC Acadia, Chevy Traverse, and Saturn Outlook), the EVAP system components are known weak points. The vent solenoid is located underneath the vehicle near the fuel tank, exposing it to road grime, salt, and moisture, which can lead to failure. The purge solenoid, located in the engine bay, is also a very common failure item that can get stuck open or, less commonly, stuck closed. GM has issued a broad Technical Service Bulletin (TSB 21-NA-124) that covers gasoline engines from 2000-2021, providing diagnostic tips for P0455 and acknowledging the commonality of component failures.

Diagnostic Flowchart

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

Symptoms You May Notice

• Check Engine Light is on
• A noticeable smell of gasoline, especially around the rear of the vehicle or near the gas cap.
• Difficulty starting the engine right after refueling (a classic sign of a stuck-open purge valve)
• Gas pump nozzle clicks off repeatedly before the tank is full (a sign of a blocked or failed vent valve that isn't allowing air to escape the tank during fueling).
• Slightly rough idle if the purge valve is stuck open, creating a vacuum leak.

Most Likely Causes

1. Loose, Damaged, or Incorrect Gas Cap 🔴 High Probability This is the most common cause for a P0455 on any vehicle. The rubber O-ring on the cap can dry out, crack, or get hard over time, preventing a proper seal. Using a non-OEM or incorrect cap can also cause this issue.
   How to confirm: First, ensure the cap is tightened until it clicks multiple times. If the code returns, visually inspect the cap's seal for cracks or damage. A smoke test will definitively show a leak from the cap area 🎬 Watch: How to pinpoint the cause of a large EVAP leak. if the seal is bad.
   Typical fix: Replace the gas cap. This is an inexpensive and simple first step. Always try an OEM or high-quality aftermarket cap.
   Est. part cost: $15-$35
2. Faulty EVAP Purge Valve/Solenoid 🟡 Medium Probability This is a very common failure point on GM vehicles of this era, including the Enclave and its platform mates. The valve can get stuck open, creating a constant vacuum leak into the intake manifold. It can also get stuck closed, which prevents the system from pulling a vacuum during its test, leading the computer to incorrectly assume there is a large leak.
   How to confirm: Remove the valve (located in the engine bay) and try to blow through it. With the vehicle off, it should be closed, and no air should pass through. If you can blow through it, it's bad. A scan tool can also command it open and closed to check for response.
   Typical fix: Replace the purge valve solenoid. It is typically held on by one bolt and is easily accessible on top of the engine. 🎬 See this quick walkthrough for replacing the purge valve.
   Est. part cost: $25-$50
3. Faulty EVAP Vent Valve/Solenoid 🟡 Medium Probability Located near the EVAP canister under the vehicle, this part is exposed to the elements (road salt, water, dirt) and can fail by getting stuck open or closed. A stuck-open vent valve will prevent the system from sealing to perform its pressure test, directly causing a P0455.
   How to confirm: A scan tool can command the valve to close during a smoke test. If smoke exits the vent valve when it's commanded closed, the valve has failed. This part is normally open when the vehicle is off; applying 12V should cause it to click closed.
   Typical fix: Replace the vent valve solenoid. It is often attached to or near the charcoal canister and may require lowering the spare tire for access. 🎬 Watch: How to replace the vent valve solenoid.
   Est. part cost: $30-$60
4. Cracked or Disconnected EVAP Hoses ⚪ Low Probability Over time, the plastic and rubber hoses in the EVAP system can become brittle and crack, especially at connection points or elbows. A user on a GM forum found a small cracked elbow hose coming from the purge solenoid was the culprit.
   How to confirm: A visual inspection may reveal obvious cracks or disconnected lines. A smoke test is the most effective way to find a leak in a hose that isn't easily visible.
   Typical fix: Replace the damaged section of hose. In some cases, a generic vacuum hose can be used for repair.
   Est. part cost: $10-$40

Rare But Worth Checking

• Cracked EVAP Charcoal Canister: The plastic housing of the canister itself can develop cracks from age or impact from road debris, creating a large leak. This can also happen if someone overtops the fuel tank, forcing liquid gasoline into the canister and ruining the charcoal media.
• Damaged Fuel Filler Neck: Rust or damage on the filler neck where the gas cap seals can prevent a proper seal, even with a new cap. On some GM vehicles, the smaller metal vent tube that runs alongside the main filler neck can rust through, causing a large leak.
• Faulty Fuel Tank Pressure Sensor: While uncommon for causing a P0455 alone, the sensor that monitors EVAP system pressure can fail and send incorrect readings to the computer, tricking it into thinking there's a leak. This will usually be accompanied by other codes specific to the sensor's circuit, such as P0451, P0452, or P0453.

Diagnosis Steps

1. Check the gas cap. Remove it, inspect the seal for cracks or hardness, and reinstall it, making sure it clicks several times. Clear the code and drive for a few days to see if it returns. This is the most common fix.
2. If the code comes back, perform a thorough visual inspection of all accessible EVAP hoses and lines under the hood and around the fuel tank area. Look for obvious cracks, damage, or disconnections. A cracked elbow hose off the purge solenoid has been a documented fix.
3. Locate and test the EVAP purge valve in the engine bay. Disconnect it and attempt to blow through it. If air passes, it is stuck open and must be replaced.
4. If the above steps do not reveal the issue, the most effective next step is to have a smoke test performed on the EVAP system.
5. During the smoke test, a technician will inject smoke into the system and use a scan tool to command the vent valve (near the tank) to close. The system is now sealed.
6. Watch for smoke leaking from the gas cap, hoses, purge valve, vent valve, or the charcoal canister itself. The source of the smoke is the source of the leak. Pay close attention to the gas cap seal and the vent solenoid outlet.

Parts You'll Likely Need

• Fuel Tank Cap (OEM #GT295 (ACDelco)) — This is the simplest and most frequent cause of a large EVAP leak due to a worn-out seal. Often the first and cheapest part to replace.
  Trusted brands: ACDelco, Stant, Gates
  OEM price range: $25-$35
  Aftermarket price range: $15-$25
• EVAP Canister Purge Valve / Solenoid (OEM #12690512) — A very common failure item on these GM vehicles. It gets stuck open, causing a permanent leak. The ACDelco part number is 214-1680, which corresponds to GM part 12597567, later superseded by 12690512 for many applications including the Enclave.
  Trusted brands: ACDelco, Dorman, SKP
  OEM price range: $35-$50
  Aftermarket price range: $25-$40
• EVAP Canister Vent Valve / Solenoid (OEM #25932571) — Its location under the vehicle makes it prone to failure from corrosion and debris, causing it to stick open. The ACDelco part number is 214-2149. This part is normally open and closes when voltage is applied.
  Trusted brands: ACDelco, Dorman
  OEM price range: $40-$60
  Aftermarket price range: $30-$50

Related Codes That Often Appear With This One

• P0442 — This code indicates a small EVAP leak. A failing component might initially cause a small leak (P0442) that worsens into a large leak (P0455). Both codes are mentioned in the same GM TSB (21-NA-124) as having similar diagnostic paths.
• P0496 — This code indicates 'High Purge Flow,' which often points directly to a purge valve that is stuck open—a very common cause for P0455 as well. If you have both codes, the purge valve is almost certainly the problem.
• P0449 — This code specifically indicates a fault in the EVAP Vent Solenoid Control Circuit. If you see P0449 along with P0455, it strongly suggests the vent solenoid or its wiring is the root cause of the leak.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-124: Provides diagnostic tips for finding EVAP leaks causing P0442 and/or P0455. It advises a specific order of operations: 1. Check all EVAP lines for proper connection. 2. Inspect lines for damage. 3. Investigate vent valve function. 4. Investigate purge valve function.

Platform-Specific Known Issues

• A wiring harness issue near the driver's side floorboard has been documented to cause a short or open in the vent solenoid circuit, leading to a P0455 code. A technician in one video found a stretched/damaged wire in this harness was keeping the vent valve open.

Mechanic-Grade Diagnostic Values

• Fuel Tank Pressure (FTP) Sensor Voltage — expected: ~1.5 V with the system at atmospheric pressure (e.g., gas cap off).. Failure: Voltage greater than 1.5V indicates vacuum; less than 1.5V indicates positive pressure. A reading that is stuck or doesn't change when conditions change indicates a faulty sensor.
• EVAP Purge Valve Solenoid Resistance — expected: Generally between 15 and 30 Ohms.. Failure: A reading significantly outside this range, or an open circuit (infinite resistance), indicates a failed solenoid coil.
• EVAP Vent Valve Solenoid Resistance — expected: Typically between 20 and 50 Ohms.. Failure: A reading far outside this range or an open circuit points to a bad solenoid coil.
• EVAP System Pressure Drop Rate (Scan Tool Data) — expected: The system should hold pressure/vacuum with minimal loss during a test.. Failure: A pressure loss rate greater than 0.2 psi/minute during a large leak test will trigger the P0455 code.

Scan Tool Commands That Help

• GDS2 / Tech2 (or equivalent professional scan tool): EVAP Service Bay Test — This is a comprehensive, automated test that runs the engine control module's entire EVAP diagnostic sequence on command, allowing a technician to monitor results in real-time without waiting for a natural drive cycle.
• GDS2 / Tech2 (or equivalent professional scan tool): Purge/Seal — This command seals the EVAP system by closing the vent valve and allows the technician to manually command the purge valve open to a specific percentage, which is essential for introducing smoke or nitrogen for leak testing.
• GDS2 / Tech2 (or equivalent professional scan tool): Vent Solenoid On/Off — Used to manually command the vent solenoid closed (On) or open (Off) to verify its function. A technician can listen for the click of the solenoid and, during a smoke test, confirm if it seals the system properly when commanded closed.

Wiring & Ground Locations

• EVAP Purge Solenoid — Center rear of the engine on the intake manifold, near the throttle body.. This is the location of the purge valve itself. Its connector and wiring are subject to engine bay heat and vibration.
• EVAP Vent Solenoid — Attached to the EVAP canister, which is located on top of the fuel tank.. The wiring for this component runs under the vehicle and is susceptible to damage from road debris, corrosion, and moisture.
• G301 — Behind the left (driver's side) kick panel.. This is a major interior ground point. A poor connection here could potentially affect circuits running through the cabin to components at the rear of the vehicle, like the vent solenoid.
• Driver's Side Floorboard Harness — Runs along the floor under the driver's side sill plate/carpet.. This harness contains wiring for the rear of the vehicle, including the vent solenoid circuit. It is a known chafe point where wires can become stretched or damaged, causing an intermittent open or short in the vent solenoid circuit, leading to a P0455 code.

Real Owner Repair Stories

• YouTube channel 'JasmineFatherGarage4k' (Buick Enclave (Lambda Platform)) — P0455 Large Leak code, along with a fuel level sensor code.
  ❌ Tried (didn't work) Initial diagnosis pointed towards common EVAP components.
  ✅ What actually fixed it The technician found a damaged/stretched gray wire inside a wiring harness located in the driver's side floorboard. Repairing this wire resolved the vent solenoid circuit fault and cleared the P0455 code.

"I Checked Everything" — The Actual Cause

• A common scenario where a smoke test shows no leaks is when the EVAP Purge Valve is stuck closed. The smoke test correctly shows the system is sealed, but during the vehicle's self-test, the ECM cannot pull the system into a vacuum because the purge valve won't open to the intake manifold. The ECM interprets this inability to achieve vacuum as a large leak, triggering P0455.
• An intermittent electrical fault in the vent solenoid circuit, such as a chafed wire in the driver's floorboard harness, can cause the P0455 code even if the system passes a smoke test. The system may seal perfectly during the test, but if the vent solenoid fails to close during a real-world drive cycle due to the wiring issue, the self-test will fail and log the code.

OEM Part Supersession History

• 12610560 → 12690512, and subsequently by 12737252 — Standard part evolution for improved reliability or manufacturing process.
  Heads up: The parts are direct replacements and should be fully compatible. When ordering, using the latest part number (12737252) is recommended.

Model Year Variations Within This Range

• 2008-2015: Within the 2008-2015 first generation, the location of the key EVAP components is consistent. The purge valve is located on top of the engine's intake manifold, making it very easy to access after removing the plastic engine cover. This differs from the second generation (2018+) where it is moved to a less accessible position behind the engine.