P0455 on 2000-2004 Buick Regal: EVAP Gross Leak Causes and Fixes

What's Unique About the 2000-2004 Buick REGAL

For the 2000-2004 Buick Regal, built on the GM W-body platform alongside the Pontiac Grand Prix and Chevrolet Impala, the P0455 code is a very common issue. The components, particularly the EVAP vent solenoid located near the rear of the car, are exposed to road salt and moisture, leading to a high failure rate. While the gas cap is always the first suspect, owners of this specific Regal generation and its platform mates frequently trace the problem to this vent solenoid.

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 car (though this is not always present).
• No noticeable impact on engine performance or drivability.
• In some related models, a faulty vent valve can cause the fuel pump to click off prematurely when refueling, even when the tank is not full.

Most Likely Causes

1. Loose, Damaged, or Incorrect Gas Cap 🔴 High Probability → Shop Fuel Tank Cap This is the most frequent cause for a P0455 code on any vehicle, as the cap is removed and replaced often, and its seal can wear out or be forgotten. Using a non-OEM cap can also cause sealing issues.
   How to confirm: Check if the gas cap is tight (it should click several times). Inspect the rubber O-ring seal on the cap for cracks, brittleness, or tearing. Ensure you are using an OEM or equivalent cap, like the ACDelco GT261.
   Typical fix: Tighten the cap. If the seal is bad, replace the entire gas cap. This is an inexpensive and simple fix. The correct OEM replacement is often ACDelco GT261.
   Est. part cost: $10-$25
2. Faulty EVAP Vent Solenoid 🟡 Medium Probability → Shop Vapor Canister On this platform, the vent solenoid is mounted near the fuel tank, often behind the rear bumper, where it is exposed to road debris, water, and salt, causing it to fail by getting stuck open. Mechanics report these fail constantly in the rust belt.
   How to confirm: Locate the solenoid near the charcoal canister by the fuel tank. It is a normally open valve. When commanded closed with a bi-directional scan tool, it should seal the system. A smoke test will show smoke exiting the vent solenoid if it's stuck open. Visually, it may be cracked or its connector corroded.
   Typical fix: Replace the EVAP vent solenoid. The common part is ACDelco 214-2149, which may come 🎬 Watch this video to see the vent solenoid replacement process. with a wiring harness adapter for an updated design. It is typically held by a single bolt.
   Est. part cost: $25-$60
3. Faulty EVAP Purge Solenoid ⚪ Low Probability → Shop Vapor Canister This valve is located in the engine bay and can fail by getting stuck open, creating a constant vacuum leak into the engine from the EVAP system.
   How to confirm: Locate the purge solenoid on the engine. Disconnect the hose leading to the intake manifold. With the engine off, you should not be able to blow through the valve. If you can, it's stuck open.
   Typical fix: Replace the purge solenoid.
   Est. part cost: $20-$50
4. Cracked or Disconnected EVAP Hoses ⚪ Low Probability Over time, the rubber and plastic hoses that make up the EVAP system can become brittle and crack, especially at connection points to the charcoal canister, filler neck, and solenoids. A user on a GM forum fixed their P0455 by replacing a small, cracked molded elbow hose from the purge solenoid.
   How to confirm: Visually inspect all accessible EVAP lines for obvious cracks, damage, or disconnections. A smoke test is the most effective way to find a small crack in a hose.
   Typical fix: Replace the damaged section of hose.
   Est. part cost: $5-$30
5. Rusted or Damaged Fuel Filler Neck ⚪ Low Probability → Shop Fuel Filler Neck The metal lip where the gas cap seals can rust or become deformed, preventing a proper seal even with a new gas cap. The entire filler neck assembly is also prone to rusting through on W-body cars, creating a large leak.
   How to confirm: After removing the gas cap, inspect the surface of the filler neck for rust, pitting, or damage that could compromise the seal. A smoke test will clearly show smoke billowing from a rusted-through filler neck pipe behind the wheel well liner.
   Typical fix: Clean the filler neck surface with a Scotch-Brite pad and apply a light film of petroleum jelly to help the seal. In severe cases of rust-through, the entire fuel filler neck must be replaced.
   Est. part cost: $50-$150

Rare But Worth Checking

• Cracked EVAP Charcoal Canister: → Shop Vapor Canister The canister itself can be damaged by road debris, leading to a large crack and a P0455 code. This is uncommon but should be visually inspected if other causes are ruled out.
• Faulty Fuel Tank Pressure (FTP) Sensor: → Shop Fuel Tank A faulty FTP sensor can incorrectly report a large leak to the ECM when one doesn't exist. This usually sets other codes alongside P0455.

Diagnosis Steps

1. Check the Gas Cap: Ensure it is tight and clicks multiple times. Remove it and inspect the seal for cracks or damage. If in doubt, replace it with a quality part (like ACDelco GT261), clear the code, and drive for a few days to see if the light returns.
2. Visual Inspection: Carefully inspect all visible EVAP hoses and lines in the engine bay and around the fuel tank/charcoal canister area. Look for any obvious cracks, holes, or disconnected lines. Pay special attention to the fuel filler neck behind the rear wheel well for signs of heavy rust.
3. Inspect the Vent Solenoid: Locate the EVAP vent solenoid near the charcoal canister at the rear of the vehicle. Check its electrical connector for corrosion and the valve itself for cracks. This is a very common failure point and the prime suspect after the gas cap.
4. Inspect the Purge Solenoid: Locate the EVAP purge solenoid in the engine bay. Check its connections and hoses.
5. Perform a Smoke Test: If the leak is not obvious, the most effective diagnostic method 🎬 See how to find leaks using a professional smoke machine. is to use an EVAP smoke machine. This tool fills the system with a harmless, visible smoke under low pressure, which will escape from the location of the leak, making it easy to pinpoint.

Parts You'll Likely Need

• Fuel Cap (OEM #ACDelco GT261) — This is the most common cause of a P0455 code due to a worn seal or improper tightening.
  Trusted brands: ACDelco, Stant, Gates
  OEM price range: $20-$30
  Aftermarket price range: $10-$20
• EVAP Vent Solenoid Valve (OEM #ACDelco 214-2149) — This part is highly susceptible to failure from corrosion and getting stuck open due to its location under the vehicle.
  Trusted brands: ACDelco, Dorman, Delphi
  OEM price range: $40-$70
  Aftermarket price range: $25-$50
• EVAP Purge Solenoid Valve — Located in the engine bay, this valve can get stuck open, causing a leak. It's less common than the vent solenoid for a large leak but is still a frequent EVAP system failure.
  Trusted brands: ACDelco, Bosch, Dorman
  OEM price range: $35-$60
  Aftermarket price range: $20-$40

Related Codes That Often Appear With This One

• P0442 — P0442 indicates a small EVAP leak. It can appear with P0455 if the system has multiple leaks or if the leak is borderline between small and large. The manufacturer TSB for this vehicle groups these two codes together. [TSB #21-NA-124]
• P0449 — This code specifically points to a fault in the EVAP Vent Solenoid Control Circuit. If you have P0455 and P0449 together, the vent solenoid is almost certainly the problem.

Technical Service Bulletins (TSBs) & Recalls

• Bulletin #21-NA-124: Mentions providing diagnostic tips for testing EVAP leaks related to DTCs P0442 and/or P0455.

Platform-Specific Known Issues

• Vulnerable Vent Solenoid Location: The EVAP vent solenoid on the 2000-2004 Regal is located behind the rear bumper/fender area, making it extremely susceptible to water, salt, and debris. This causes the solenoid to corrode and fail, getting stuck open and triggering the P0455 code. The replacement is simple, often held by just one 10mm bolt, but access can be tight.

Mechanic-Grade Diagnostic Values

• Fuel Tank Pressure (FTP) Sensor Voltage — expected: 1.3 to 1.7 Volts with the sensor at atmospheric pressure (disconnected from the tank, key on).. Failure: A reading of 0V or 5V suggests a wiring problem or a failed sensor. A reading stuck at a low value when vacuum is applied indicates a bad sensor.
• EVAP Purge Solenoid Resistance — expected: Approximately 15 to 30 Ohms.. Failure: A reading significantly outside this range, or an open/infinite reading, indicates a failed solenoid coil.
• FTP Sensor Connector Voltage — expected: With the sensor unplugged and key on: one pin should have 5V (reference), one should have 0V (ground), and the third is the signal wire.. Failure: Missing the 5V reference or ground indicates a wiring issue from the ECM, not a bad sensor.

Scan Tool Commands That Help

• GM Tech 2: EVAP Service Bay Test — This is a forced functional test to verify the integrity of the entire EVAP system without needing to perform a full drive cycle. It commands the vent and purge solenoids to seal the system and monitors the FTP sensor to check if vacuum holds. NOTE: Per TSB #02-06-04-014, GM removed this test for 2000-2001 Regal models due to accuracy issues, so it may not be available.

Wiring & Ground Locations

• Main Engine Grounds — A group of ground wires with ring terminals are typically attached to the rear of the passenger side cylinder head and/or the top transmission bellhousing bolts.. These grounds are critical for the ECM and multiple sensors. A poor connection here can cause erratic sensor readings and incorrect diagnostic codes.
• Chassis Grounds — Check for ground busses located under the carpet near the front door sills on both the driver and passenger sides.. Corrosion at these interior ground points is common and can cause various difficult-to-diagnose electrical issues.
• FTP Sensor Connector — On top of the fuel tank, part of the fuel pump module assembly. Wires are typically Gray (5V reference), Dark Green (signal), and Tan (ground).. This is the direct connection for the sensor that measures system pressure. Verifying power, ground, and signal here is key to diagnosing a faulty sensor vs. a wiring problem.

Real Owner Repair Stories

• YouTube channel Salem Doyle (Buick Regal (generation consistent with 2000-2004)) — Check Engine Light on.
  ❌ Tried (didn't work) The video directly addresses the EVAP code as a primary issue to fix.
  ✅ What actually fixed it Replaced the EVAP vent solenoid located behind the rear bumper. The video shows the tight location and the single bolt holding the bracket.

OEM Part Supersession History

• 25932571 → ACDelco 214-2149 — Part number consolidation and potential design updates.
  Heads up: The Pass 2 data notes that the replacement part may come with a wiring harness adapter, suggesting the connector design was changed on the new part number. This is a critical detail for installation.
• Unknown → Dorman 911-021, Standard Ignition CVS6 — Aftermarket cross-references for ACDelco 214-2149.

Model Year Variations Within This Range

• 2000-2001: The 'EVAP Service Bay Test' was removed from the official GM Tech 2 software for these model years due to concerns about inaccurate results, per TSB #02-06-04-014. Diagnosis may require a full drive cycle to run the EVAP monitor.
• 2003-2004: The transmission and PCM were changed in 2003. While not a direct EVAP component change, the PCM software dictates when the EVAP monitor tests are run, so the conditions required to complete a drive cycle may differ slightly from earlier models.