P0455 on 2019-2023 Cadillac XT4: EVAP Gross Leak Causes & Fixes

What's Unique About the 2019-2023 Cadillac XT4

For the 2019-2023 Cadillac XT4, the P0455 code is a straightforward emissions issue without major platform-specific oddities. 🎬 Watch: A quick overview of P0455 causes and common fixes. However, General Motors has issued a Technical Service Bulletin (TSB #21-NA-124) that provides technicians with specific diagnostic tips for finding EVAP leaks on this model, which suggests that pinpointing the exact source can sometimes be tricky. The core components (gas cap, purge valve, vent solenoid) are the usual suspects, as with most GM vehicles.

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 illuminated
• A faint smell of fuel, especially around the rear of the vehicle
• No noticeable impact on drivability or engine performance

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 vehicles, as it's the most frequently removed and reinstalled part of the sealed EVAP system.
   How to confirm: Ensure the gas cap is tightened until it clicks. Inspect the cap's seal for cracks, tearing, or signs of wear. The Cadillac XT4 has a capless fuel filler system, so inspect the spring-loaded flap for debris or damage that prevents a proper seal.
   Typical fix: Tighten the cap or clean the sealing flap. If the seal is damaged or the cap is faulty, replace it.
   Est. part cost: $20-$50
2. Faulty EVAP Purge Valve/Solenoid 🟡 Medium Probability The purge valve is a common failure point on many GM vehicles. It can get stuck open, creating a large leak path from the EVAP system to the engine intake.
   How to confirm: The purge valve is located in the engine bay. With the engine off, disconnect the valve and try to blow through it. If air passes through, the valve is stuck open and has failed. A scan tool can also be used to command the valve closed and check for vacuum.
   Typical fix: Replace the purge valve solenoid.
   Est. part cost: $25-$70
3. Faulty EVAP Vent Valve/Solenoid 🟡 Medium Probability This valve is located near the charcoal canister at the rear of the vehicle and is exposed to road debris and moisture, which can cause it to fail or get stuck. If it fails to close during the system's self-test, it will be registered as a large leak.
   How to confirm: A smoke test is the most effective method. A scan tool can be used to command the valve to close; if smoke still escapes from the vent, the valve is faulty. Visual inspection for cracks or damage is also recommended.
   Typical fix: Replace the vent valve solenoid. 🎬 See this walkthrough on replacing the XT4 vent solenoid.
   Est. part cost: $30-$80
4. Cracked or Disconnected EVAP Hose ⚪ Low Probability Plastic and rubber hoses can become brittle over time due to heat and age, leading to cracks. A disconnected line can also occur during other maintenance.
   How to confirm: A thorough visual inspection of all EVAP lines between the engine, charcoal canister, and fuel tank. A smoke test is the definitive method to find a cracked or leaking hose that isn't visually obvious.
   Typical fix: Replace the damaged section of hose or the entire line.
   Est. part cost: $15-$100

Rare But Worth Checking

• Cracked EVAP Charcoal Canister: The canister itself can be damaged by road debris, causing a crack and a large leak. This is uncommon but should be checked if other components are confirmed to be working.
• Damaged Fuel Filler Neck: Corrosion or damage to the filler neck where the capless system seals can prevent a proper seal, leading to a leak.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0455 is present.
2. Inspect the capless fuel filler neck for any debris or damage that could prevent the flap from sealing. Clean it and ensure it moves freely.
3. Visually inspect the EVAP purge solenoid in the engine bay and its connected hoses for any obvious cracks or disconnections.
4. Visually inspect the EVAP charcoal canister and vent solenoid under the rear of the vehicle for any signs of physical damage.
5. If the leak source is not obvious, a smoke test is the most effective diagnostic procedure. This involves injecting low-pressure smoke into the EVAP system and looking for where it escapes.
🎬 Watch: How to perform a professional EVAP smoke test.
6. Use a scan tool to monitor the fuel tank pressure sensor and to command the purge and vent valves, which can help isolate the faulty component.

Parts You'll Likely Need

• EVAP Canister Purge Valve (OEM #12666845) — This valve frequently gets stuck open, causing a constant leak path that the system detects as a P0455 code. It is a common failure item on many GM vehicles.
  Trusted brands: ACDelco, Standard Motor Products
  OEM price range: $30-$50
  Aftermarket price range: $20-$40
• EVAP Canister Vent Solenoid (OEM #85123399) — Located near the fuel tank, this part is exposed to the elements and can fail, preventing the EVAP system from sealing for its pressure test.
  Trusted brands: ACDelco, Dorman, Standard Motor Products
  OEM price range: $40-$70
  Aftermarket price range: $25-$50

Related Codes That Often Appear With This One

• P0442 — P0442 indicates a small EVAP leak. Sometimes a component on the verge of failing may initially cause a small leak code before it worsens and triggers a large leak code like P0455.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #21-NA-124: Provides diagnostic tips/steps 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.

Platform-Specific Known Issues

• GM has issued Technical Service Bulletin #21-NA-124, which provides diagnostic tips for technicians dealing with P0442 and P0455 codes on the 2019 Cadillac XT4, among other models. This indicates that finding the source of the leak may require specific procedures beyond a simple visual inspection.

Mechanic-Grade Diagnostic Values

• Fuel Tank Pressure (FTP) Sensor Voltage — expected: 1.3 - 1.7 Volts (typically 1.5V) with key on, engine off, and fuel cap removed (atmospheric pressure).. Failure: A reading significantly outside this range, or one that is stuck, suggests a faulty sensor or wiring issue.
• FTP Sensor 5-Volt Reference Circuit — expected: 4.8 - 5.2 Volts between the reference circuit pin and a known good ground.. Failure: Low or no voltage points to a problem with the ECM or the wiring from the ECM.
• EVAP Vent Valve Solenoid Resistance — expected: Between 20 and 30 Ohms across the two terminals.. Failure: A reading far outside this range or an open circuit (OL) indicates a failed solenoid coil.
• EVAP Purge Valve Solenoid Resistance — expected: Between 15 and 30 Ohms across the two terminals.. Failure: A reading significantly outside this range indicates a damaged internal circuit.

Scan Tool Commands That Help

• GDS2 / Tech 2: EVAP Purge/Seal — This is a bidirectional control function used to manually diagnose the system. A technician can command the vent valve to 'Seal' the system and then command the purge valve to open by a certain percentage to create a vacuum. By monitoring the Fuel Tank Pressure (FTP) sensor voltage, the technician can determine if the system is holding vacuum, which helps isolate the location of a leak without a smoke machine.

Wiring & Ground Locations

• EVAP Canister Vent Solenoid — Located at the rear of the vehicle, behind the passenger-side rear fender liner, mounted on or near the charcoal canister.. This is a key component for sealing the EVAP system for a leak test. Its location makes it susceptible to road debris and moisture, which can damage the component or its wiring connector, causing a P0455 leak code.
• EVAP Canister Purge Valve — Located in the engine bay, typically on or near the engine intake manifold.. This valve controls the flow of vapors to the engine. If it sticks open, it creates a large, permanent leak path that is immediately detected by the ECM, triggering a P0455 code.

OEM Part Supersession History

• 22740537, 84065747, 84802774, 85123403 → 85123399 — Standard part consolidation and revision by the manufacturer.