P0455 on 2000-2005 Buick Century: EVAP Large Leak Causes and Fixes

What's Unique About the 2000-2005 Buick CENTURY

On this generation of Buick Century and other GM W-body vehicles from this era (like the Pontiac Grand Prix and Chevy Impala), the EVAP system components, particularly the vent and purge solenoids, are common failure points. The vent solenoid, located near the fuel tank, is exposed to road debris and moisture, causing it to fail and stick open, which the system interprets as a large leak. The purge solenoid, located in the engine bay, can also get stuck, but the vent solenoid is a more frequent cause for this specific code. Furthermore, the steel fuel filler neck is highly susceptible to rusting through in areas where road salt is used, creating a large leak that is often misdiagnosed.

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 fuel, especially around the rear of the car or after parking in a garage
• Slight decrease in fuel economy over time
• Difficulty refueling where the gas pump nozzle clicks off repeatedly before the tank is full (a classic sign of a stuck-closed vent solenoid).

Most Likely Causes

1. Loose, Damaged, or Incorrect Gas Cap 🔴 High Probability → Shop Fuel Tank Cap The gas cap is the most frequently handled part of the EVAP system, and its seal can degrade over time or it may not be tightened properly after refueling. This is the most common cause of P0455 on most GM vehicles.
   How to confirm: Check if the gas cap clicks at least three times when tightened. Inspect the rubber seal on the cap for cracks, stiffness, or damage. If the seal is compromised, the cap needs replacement. A temporary test can be to apply a thin layer of petroleum jelly to the seal to see if it helps.
   Typical fix: Tighten the cap correctly or replace it with a new OEM-spec cap. Aftermarket caps can sometimes have sealing issues.
   Est. part cost: $10-$25
2. Faulty EVAP Canister Vent Solenoid/Valve 🟡 Medium Probability → Shop Vapor Canister This valve is located underneath the vehicle near the charcoal canister and is highly exposed to road salt, water, and debris, leading to corrosion and failure. It can get stuck open, causing a large leak code, or stuck closed, causing refueling issues.
   How to confirm: The valve is normally open and should close when voltage is applied. A mechanic can command it closed with a scan tool to check its function. It can also be removed and tested by applying 12V to see if it actuates with an audible click.
   Typical fix: Replace the canister vent solenoid. This is a very common repair for this vehicle and its platform mates.
   Est. part cost: $25-$60
3. Faulty EVAP Purge Solenoid/Valve 🟡 Medium Probability → Shop Vapor Canister Located in the engine bay, this valve can get stuck open or, less commonly, stuck closed. If stuck open, it creates a constant vacuum leak into the intake manifold. If stuck closed, the system cannot pull a vacuum during its test, which the ECM can misinterpret as a massive leak.
   How to confirm: The valve is normally closed. Disconnect the hose leading to the intake manifold and check for vacuum with the engine running; there should be none at idle. You can also remove it and try to blow through it; if air passes, it's stuck open and faulty.
   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 in the EVAP system can become brittle and crack, especially the molded elbow hoses connected to the purge solenoid in the engine bay due to heat.
   How to confirm: A visual inspection may reveal obvious cracks or disconnections, particularly at connection points. A smoke test is the most effective method, where a machine fills the EVAP system with visible smoke, making any leaks easy to spot.
   Typical fix: Replace the cracked section of hose or the entire hose assembly. A user on a GM forum reported fixing their P0455 by replacing a small, cracked molded hose at the purge solenoid.
   Est. part cost: $5-$30

Rare But Worth Checking

• Cracked Charcoal Canister: → Shop Vapor Canister The plastic housing of the charcoal canister (ACDelco P/N 215-464) can crack from age or impact, creating a large leak. This is usually found during a smoke test if other components check out. Debris from a failing canister can also contaminate and destroy new purge or vent valves.
• Leaking Fuel Tank Filler Neck: → Shop Fuel Tank The metal tube where you insert the fuel nozzle can rust and develop holes, especially in regions where road salt is used. This creates a leak that is often mistaken for a bad gas cap. A visual inspection under the car, often requiring removal of a plastic shield, will reveal heavy rust or pinholes.
• Faulty Fuel Tank Pressure (FTP) Sensor: → Shop Fuel Tank While less common for P0455, the sensor itself can fail and provide incorrect readings to the ECM, tricking it into thinking there is a large leak. This often sets other codes along with P0455 and is typically located on top of the fuel pump module.

Diagnosis Steps

1. Inspect the Gas Cap: Ensure it is tight. Remove it and check the seal for any cracks or damage. If in doubt, it's an inexpensive part to replace as a first step. An OEM cap is recommended.
2. Clear the Code: After checking/replacing the cap, clear the code with a scanner and drive for a few days (multiple drive cycles) to see if it returns. The light will not turn off immediately.
3. Visual Inspection: Look over all accessible EVAP hoses in the engine bay and under the car near the fuel tank for obvious cracks, rot, or disconnections. Pay close attention to the fuel filler neck for signs of severe rust.
4. Test the Purge Solenoid: Locate the purge solenoid on top of the engine. With the engine off, unplug the electrical connector and try to blow through the valve. If air passes, it is stuck open and needs to be replaced.
5. Test the Vent Solenoid: Locate the vent solenoid near the charcoal canister by the fuel tank. It is normally open. A scan tool can command it closed to test function. Alternatively, it can be removed and tested by applying 12V power; it should click closed.
6. Perform a Smoke Test: If the above steps do not reveal the leak, the most reliable method is to have a smoke test performed. A machine injects harmless, visible smoke into the EVAP system, and the leak will be visible wherever the smoke escapes. This is the definitive way to find cracked hoses or a leaky filler neck.

Parts You'll Likely Need

• Gas Cap (OEM #ACDelco GT254) — This is the most common cause of a P0455 code due to improper tightening or a worn-out seal.
  Trusted brands: ACDelco, Stant
  OEM price range: $15-$30
  Aftermarket price range: $10-$20
• EVAP Canister Vent Solenoid Valve (OEM #ACDelco 214-2149) — This part is highly prone to failure from its location under the car. It gets stuck open, causing the system to fail its pressure test.
  Trusted brands: ACDelco, Dorman (911-021), Standard Motor Products (CVS6)
  OEM price range: $40-$70
  Aftermarket price range: $25-$50
• EVAP Canister Purge Solenoid Valve (OEM #ACDelco 214-646) — This valve, located on the engine, can get stuck open, causing a leak that the system detects during self-tests. It can also get clogged with charcoal debris from a failing canister.
  Trusted brands: ACDelco, Standard Motor Products, Wells
  OEM price range: $30-$60
  Aftermarket price range: $20-$45

Related Codes That Often Appear With This One

• P0442 — P0442 indicates a small EVAP leak. Sometimes a component is beginning to fail and may initially set a P0442 before the leak worsens and triggers a P0455. The official GM TSB 21-NA-124 for this issue groups P0442 and P0455 together as part of the same diagnostic procedure.
• P0446 — This code points specifically to a fault in the EVAP vent control circuit or system. If you have P0455 and P0446 together, it strongly suggests the problem is with the vent solenoid or its wiring, as the ECM has detected both a large leak and a problem with the vent circuit's performance.
• P0449 — Similar to P0446, this code indicates a malfunction in the EVAP vent valve/solenoid control circuit. Seeing this with P0455 makes the vent solenoid the primary suspect.

Technical Service Bulletins (TSBs) & Recalls

• 21-NA-124: "Diagnostic Tip for Malfunction Indicator Lamp (MIL) Illuminated - DTC P0442 and/or P0455 Set." This TSB outlines a logical diagnostic flow: check connections, check lines for damage, test the vent valve, then test the purge valve.
• 02-06-04-037: An older GM bulletin that also covers EVAP codes including P0455, often pointing towards issues with the vent solenoid, purge solenoid, or their related wiring and hoses.

Platform-Specific Known Issues

• Rusted Fuel Filler Neck: → Shop Fuel Filler Neck In regions with winter road salt ('Rust Belt'), the steel fuel filler neck is a very common failure point. It rusts through, creating a large leak that triggers P0455. Many owners mistakenly replace the gas cap multiple times before discovering the rusted neck is the actual cause. A thorough visual inspection is required. A video of a replacement on a similar GM vehicle shows this failure mode clearly.

Mechanic-Grade Diagnostic Values

• EVAP Purge Solenoid Coil Resistance — expected: 11 to 26 Ohms. Failure: Resistance is significantly outside this range, or shows an open or shorted circuit.
• EVAP Vent Solenoid Power Supply (Key On, Engine Off) — expected: 12V (Battery Voltage). Failure: No voltage at the power feed wire indicates a wiring or fuse issue upstream of the solenoid.
• Fuel Tank Pressure (FTP) Sensor Voltage (Atmospheric Pressure) — expected: ~1.5 Volts. Failure: A voltage significantly different from 1.5V with the system at rest (not under vacuum or pressure) can indicate a faulty sensor.
• Fuel Tank Pressure (FTP) Sensor Signal Range — expected: 0.1 - 4.9 Volts. Failure: A signal stuck at either extreme suggests a sensor or wiring fault. A signal greater than 4.9V can trigger a P0453 code.

Scan Tool Commands That Help

• GM Tech2: EVAP Service Bay Test — This function forces the vehicle's PCM to run the entire EVAP monitor test sequence while in the service bay, verifying system integrity after a repair without needing a full drive cycle. It commands the vent and purge solenoids to seal the system and monitors for pressure decay.
• GM Tech2 / Professional Scan Tool: EVAP Vent Solenoid ON/OFF — This is a bidirectional control used to manually command the normally-open vent solenoid to close. This is a critical first step before performing a smoke test to ensure the system is sealed for the test.
• GM Tech2 / Professional Scan Tool: EVAP Purge Solenoid Command — Allows the technician to command the normally-closed purge solenoid to open by a specific percentage. This is used to verify the solenoid is not stuck and is capable of drawing vapor from the canister.

Wiring & Ground Locations

• EVAP Canister Vent Solenoid — Behind the left side of the rear fascia splash shield, in the wheel well area.. This component's location makes it and its connector highly susceptible to corrosion from road salt and water, which can cause it to fail electrically or mechanically, leading to a P0455.
• EVAP Canister Purge Solenoid (3.1L V6) — Top right side of the engine, behind the ignition control module.. This solenoid controls vapor flow to the engine. A failure here can cause a leak. Knowing its location is key for testing and replacement.
• G111 (3.1L V6) — Lower left front of the engine, on a transaxle stud, to the left of the starter.. This is a primary engine ground. While not directly for the rear EVAP components, a poor ground here can cause erratic PCM behavior and misinterpretation of sensor data, potentially leading to false codes.
• G402 — On the right side of the rear package shelf, accessible from the trunk.. This is a key body ground in the rear of the vehicle. The EVAP vent solenoid and fuel tank pressure sensor rely on a clean ground path. Corrosion at this point can cause intermittent operation of the vent solenoid.

Real Owner Repair Stories

• Chevy Colorado owner on DoItYourself.com forums (2007 Chevy Colorado (similar GM EVAP system)) — P0455 and P0449 codes present.
  ❌ Tried (didn't work) Replaced purge valve solenoid, Replaced gas cap, Replaced canister vent valve, Performed a smoke test which showed no leaks
  ✅ What actually fixed it The final fix was not posted, but a responding technician suggested checking for broken wires right at the vent valve connector, noting they can make intermittent contact and cause faults even when a smoke test passes and power is present during a simple check.

"I Checked Everything" — The Actual Cause

• In some cases, a vehicle can pass a smoke test but still set a P0455 code. This often points to an intermittent electrical problem rather than a constant physical leak. A common culprit is a broken wire inside the insulation near the EVAP vent solenoid connector, which makes and breaks contact as the vehicle moves. Another possibility is a faulty Fuel Tank Pressure (FTP) sensor that gives erroneous readings, or a PCM that is not correctly interpreting the sensor data, though this is less common.

OEM Part Supersession History

• 25932571 → ACDelco 214-2149 — Part number consolidation and potential design updates for the EVAP Canister Vent Solenoid.

Model Year Variations Within This Range

• 2000-2002: According to GM Technical Service Bulletin #02-06-04-014, the 'EVAP Service Bay Test' function was eliminated from the Tech2 scan tool for many 2000-2002 GM models, including the Buick Century. This means that for these years, a technician cannot force the EVAP monitor to run in the shop and must use a standard drive cycle to verify a repair.