P0455 on 2017-2023 Cadillac XT5: EVAP Large Leak Causes and Fixes

What's Unique About the 2017-2023 Cadillac XT5

For the Cadillac XT5 and its platform mates (Chevy Traverse, GMC Acadia), GM has issued Technical Service Bulletins (TSBs) addressing diagnostics for P0455, indicating it's a known issue. TSB #21-NA-124 provides a specific diagnostic hierarchy for EVAP leaks. TSB #PIE0528 requests field information on canister-related failures, suggesting the EVAP canister and its associated valves are a point of interest for this platform. The purge valve, in particular, is a very common failure point on GM's 3.6L V6 engine. Additionally, 2020 models with the 2.0L LSY engine have a special warranty extension to 15 years/150,000 miles for the evaporative emissions purge pump due to a known failure pattern.

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 fuel smell, especially around the rear of the vehicle.
• Rough idle, stalling, or difficulty starting, particularly right after filling the gas tank (strong indicator of a bad purge valve).
• Difficulty filling the fuel tank (the pump may click off repeatedly before the tank is full), which often points to a faulty vent valve or blocked canister.

Most Likely Causes

1. Loose, Damaged, or Incorrect Gas Cap 🔴 High Probability This is the most common cause for a P0455 code on virtually all modern vehicles, as the cap is the most frequently moved part of the sealed system.
   How to confirm: Inspect the gas cap for cracks or damage to the seal. Ensure it is tightened until it clicks at least once. Even if it looks good, the seal can fail with age. A replacement cap is an inexpensive diagnostic step.
   Typical fix: Tighten or replace the gas cap.
   Est. part cost: $15-$40
2. Faulty EVAP Purge Solenoid/Valve 🔴 High Probability This is a very common failure item on the 3.6L V6 engine used in the XT5 and its platform mates. The valve gets stuck open, creating a constant vacuum leak which the ECM detects as a large leak and often causes rough running after refueling.
   How to confirm: The purge valve is located on the engine, usually near the throttle body. A key symptom is a rough idle or stalling right after a fill-up. To test, remove the valve (when the engine is off) and try to blow through it; if air passes, it's stuck open and needs replacement. A bi-directional scan tool can also command the valve to cycle for testing. Note: Newer 2.0L engines may use a different style valve that can be misdiagnosed; see Model-Year Variations.
   Typical fix: Replace the purge solenoid valve. 🎬 See this step-by-step guide to replacing the purge solenoid.
   Est. part cost: $30-$85
3. Faulty EVAP Vent Solenoid/Valve 🟡 Medium Probability
   How to confirm: The vent solenoid is located under the vehicle, attached to or near the EVAP canister by the fuel tank. It can fail by getting stuck open, preventing the system from sealing itself for a test. A symptom can be the fuel pump nozzle clicking off repeatedly during fueling. It can be tested with a scan tool or by applying 12V to see if it actuates (it's normally open and should close with power).
   Typical fix: Replace the vent solenoid. 🎬 Watch: How to replace a faulty vent valve solenoid.
   Est. part cost: $30-$60
4. Cracked or Disconnected EVAP Hoses ⚪ Low Probability
   How to confirm: Visually inspect all accessible EVAP lines between the engine, canister, and fuel tank for obvious cracks, brittleness, or disconnections. TSB #21-NA-124 specifically calls out checking for improperly seated connections first. A professional smoke test is the most reliable way to find a hard-to-see leak in the hose network.
   Typical fix: Replace the damaged section of hose or re-secure the connection.
   Est. part cost: $10-$50
5. Leaking EVAP Canister ⚪ Low Probability TSB #PIE0528 specifically mentions the EVAP canister, suggesting it can be a failure point on these vehicles. The plastic body can be damaged by road debris.
   How to confirm: A smoke test is the best method. Smoke will be seen exiting from a crack in the canister body. Also inspect for any visible physical damage.
   Typical fix: Replace the EVAP canister.
   Est. part cost: $150-$350

Rare But Worth Checking

• Cracked Fuel Filler Neck: Rust or physical damage can cause the metal filler neck to crack or deform, preventing the gas cap from creating a proper seal.
• Leaking Fuel Tank: While rare, a crack in the fuel tank or a bad seal at the fuel pump assembly will cause a P0455 code and a strong fuel odor.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0455 is present.
🎬 Watch: A real-world diagnostic walkthrough for the XT5 P0455 code.
2. Inspect the gas cap. Remove it, check for cracks in the seal, and retighten it until it clicks several times. Clear the code and drive. If the code returns, it's a good, inexpensive first step to replace the cap.
3. Perform a visual inspection of EVAP lines as recommended by TSB #21-NA-124. Check all accessible hoses and lines from the engine bay to the fuel tank. Pay close attention to connection points to ensure they are fully seated. Look for obvious cracks or damage.
4. Test the EVAP vent solenoid. Located near the charcoal canister, this valve is normally open. A scan tool can command it closed for testing. If you have difficulty filling your fuel tank, this part is a high-probability suspect.
5. Test the EVAP purge solenoid. Located on the engine, this valve is normally closed (on 3.6L engines). If you experience a rough idle after refueling, this is the most likely cause. Remove the valve and try to blow through it; if air passes, it has failed.
6. If the leak source is still not found, perform a smoke test. This involves injecting pressurized smoke into the EVAP system's service port and looking for where the smoke escapes. This is the most definitive way to find leaks in hoses, the canister, the filler neck, or the fuel tank.

Parts You'll Likely Need

• Gas Cap (OEM #ACDelco GT330 (Verify by VIN)) — This is the most frequent cause of a P0455 code due to being frequently handled, worn, or improperly tightened.
  Trusted brands: ACDelco, Gates, Stant
  OEM price range: $25-$40
  Aftermarket price range: $15-$30
• EVAP Canister Purge Solenoid Valve (OEM #12666845 or 12630282 (Verify by VIN)) — This valve cycles frequently and is a common failure point on the 3.6L engine, often getting stuck open and causing a large leak code and rough idle after fueling.
  Trusted brands: ACDelco, Standard Motor Products, Dorman
  OEM price range: $35-$75
  Aftermarket price range: $25-$50
• EVAP Canister Vent Solenoid (OEM #23481275 or 85123399 (Verify by VIN)) — Located near the rear of the vehicle, this valve can fail due to exposure to road debris and moisture, causing it to stick open and prevent the system from sealing.
  Trusted brands: ACDelco, Standard Motor Products, Dorman
  OEM price range: $40-$80
  Aftermarket price range: $30-$60
• EVAP Vapor Canister (OEM #85572069 (2017-2019), 85158843 (2020-2024) (Verify by VIN)) — Though less common, the canister can crack from road debris impact, causing a large leak. TSB #PIE0528 indicates this is a known, if less frequent, failure point.
  Trusted brands: ACDelco (GM Genuine)
  OEM price range: $160-$360
  Aftermarket price range: $150-$250

Related Codes That Often Appear With This One

• P0442 — This code is for a small EVAP leak. It can appear alongside P0455 if the system has multiple leaks or if the size of the leak is borderline between small and large. TSB #21-NA-124 mentions both codes together.
• P0496 — This code indicates 'EVAP Flow During a Non-Purge Condition,' which points directly to a faulty purge valve that is stuck open or leaking. It is very commonly seen with P0455 when the purge valve is the cause.
• P0446 — This code relates to the EVAP Vent Control Circuit. A faulty vent solenoid can cause both a P0446 and a P0455. TSB #PIE0528 lists these codes together.
• P146C / P146F — On newer models with the 2.0L engine, these manufacturer-specific codes for 'EVAP Purge Pump Performance' and 'EVAP Purge System Pressure Sensor Performance' may accompany a P0455, pointing to an issue with the auxiliary purge pump system.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-124: Diagnostic tips on testing for possible EVAP leaks in the system to correct a customer concern of an MIL Illuminated with DTCs P0442 and/or P0455 Set.
• PIE0528: Engineering informational bulletin requesting information from the field on warranty parts for complete canister

Platform-Specific Known Issues

• NHTSA Technical Service Bulletin #21-NA-124 provides dealers with a specific diagnostic hierarchy for P0455/P0442: check EVAP line connections first, then check for line damage, then test the vent valve, and finally test the purge valve.
• NHTSA Technical Service Bulletin #PIE0528 was an informational bulletin requesting data on EVAP canister failures related to a group of codes including P0455, indicating a potential pattern of issues with this component on GM vehicles.
• A rough idle or stalling immediately after refueling is a very common owner complaint on this platform that almost always points to a stuck-open EVAP purge valve.
• Cadillac has extended the warranty on the evaporative emissions purge pump for 2020 XT5 models with the 2.0L LSY engine to 15 years or 150,000 miles. This was done due to a high failure rate causing the Check Engine Light.

Mechanic-Grade Diagnostic Values

• EVAP Purge or Vent Solenoid Coil Resistance — expected: 15 - 30 Ohms. Failure: A reading far outside this range, or an open circuit (infinite resistance), indicates a failed solenoid coil.
• EVAP Vent Solenoid Power Supply — expected: 12V+ at the connector with key on, engine off.. Failure: No voltage indicates a wiring or fuse issue upstream of the solenoid.

Hidden / Shadow Codes Worth Checking

• P146C: EVAP Purge Pump Performance. Indicates a problem with the auxiliary EVAP purge pump. (see via Standard OBD-II scanner. Seen on 2020+ models with the 2.0L Turbo engine.)
• P146F: EVAP Purge System Pressure Sensor Performance. Indicates an issue with the pressure sensor related to the purge pump system. (see via Standard OBD-II scanner. Seen on 2020+ models with the 2.0L Turbo engine.)

Scan Tool Commands That Help

• GDS2 / Professional Scan Tool: EVAP System Test / Purge/Seal — This command seals the EVAP system (by closing the vent solenoid) and allows the technician to monitor the fuel tank pressure sensor to see if the system holds a vacuum, confirming a leak is present.
• GDS2 / Professional Scan Tool: EVAP Purge Solenoid Control — Allows the technician to command the purge solenoid open and closed to verify its mechanical and electrical operation. On a 2017 XT5, a user identified a 'malfunction' using this type of command on a Maxus scanner.
• GDS2 / Professional Scan Tool: EVAP Vent Solenoid Control — Allows the technician to command the normally-open vent solenoid to close. This is essential for sealing the system for a smoke test or pressure test. If the system won't seal, this command can help determine if the valve is stuck or not receiving the signal.

Real Owner Repair Stories

• YouTube user James Saber (2017 Cadillac XT5) — Check Engine Light with code P0455.
  ✅ What actually fixed it The user diagnosed the issue using a Maxus scan tool. In the engine control module functions, the test for the 'evaporative emission evap system purge' showed a 'malfunction' when commanded, directly indicating the purge solenoid was the faulty component.
• YouTube user AG AUTOMOTIVE (2023 Cadillac XT5, 2.0L engine) — Check Engine Light with codes P146C & P146F.
  ❌ Tried (didn't work) The technician initially replaced the purge solenoid because air could be blown through it when it was removed from the vehicle, a classic test for a stuck-open valve on older designs.
  ✅ What actually fixed it The technician researched and discovered the new style purge valve on the 2.0L engine has a diagnostic port between the o-rings that will allow air to pass through when off the vehicle. This is normal. The original diagnosis was incorrect, and the video serves as a warning about this diagnostic trap. The technician then proceeded to test the EVAP purge pump with a scan tool, which was the next logical step.

OEM Part Supersession History

• 12630282 (and others) → 12666845 — Part consolidation and potential design updates. Part 12666845 is listed for many GM vehicles from 2019 onwards, including the XT5 with the 2.0L engine.
  Heads up: Verify part by VIN. While 12666845 may be the latest number, the physical fitment and control strategy could differ between the 3.6L V6 and 2.0L Turbo engines. The valve for the 2.0L has a different design that can be misdiagnosed.

Model Year Variations Within This Range

• 2020-2023 (with 2.0L LSY Engine): These models feature an auxiliary 'EVAP Purge Pump' in addition to the standard components. This pump has a high failure rate, leading Cadillac to issue a special 15-year/150,000-mile warranty extension. The purge solenoid valve on these engines is also a different design and can be easily misdiagnosed as faulty using traditional methods.
• 2017-2019 vs 2020-2024: The OEM part number for the EVAP Vapor Canister changes between these year groups. 2017-2019 models use PN 85572069, while 2020-2024 models use PN 85158843, suggesting a design change coinciding with the mid-cycle refresh and engine lineup update.