P0455 on 2017-2018 Alfa Romeo Giulia: EVAP Large Leak Causes and Fixes

What's Unique About the 2017-2018 Alfa Romeo GIULIA

While the causes for P0455 are common across many vehicles, on the Giulia and its platform-mate, the Stelvio, this code is specifically mentioned in several Technical Service Bulletins (TSBs). These TSBs often involve a software update for the Powertrain Control Module (PCM) to improve the diagnostic logic for a range of codes, including P0455. This suggests that in some cases, the code may be triggered due to sensitive software rather than a major hardware failure. However, physical leaks remain the most common cause, with forum discussions pointing to a higher-than-average failure rate for the charcoal canister on this platform. The difficulty in refueling is a very common symptom pointing to a failed canister on these cars.

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 after refueling or when parked in a garage.
• Slightly reduced fuel economy
• Difficulty refueling (gas pump nozzle clicks off repeatedly before the tank is full).
• A 'permanent' code that may not clear with a standard scanner until the onboard monitor completes its self-test over several drive cycles.

Most Likely Causes

1. Loose or Faulty Gas Cap 🔴 High Probability This is the most common cause for a P0455 code on any vehicle, including the Giulia. The rubber seal on the cap can degrade over time, or it may simply not have been tightened correctly. An aftermarket company even sells a specific replacement seal for the OEM Giulia/Stelvio cap, indicating this is a frequent failure point.
   How to confirm: Ensure the gas cap is tightened until it clicks several times. Inspect the rubber O-ring seal on the cap for cracks, brittleness, or deformation. If the light returns after tightening and clearing the code, the cap seal is likely faulty.
   Typical fix: Replace the gas cap or just the rubber seal. Resealing the factory cap is often preferred to avoid issues with poorly fitting aftermarket caps.
   Est. part cost: $10 (seal only) - $40 (full OEM cap)
2. Cracked or Failed Charcoal Canister 🟡 Medium Probability Owners on forums like Reddit and GiuliaForums have reported a relatively high failure rate for the charcoal canister on the Giulia. One owner mentioned their dealer confirmed it's a known issue, with their own car needing two replacements. A related code, P2422 (EVAP Vent Valve Stuck Closed), is also a tell-tale sign of a failing canister on this platform. The canister assembly includes the vent valve, and failure often leads to difficulty refueling.
   How to confirm: A visual inspection may reveal cracks or damage on the canister body, located in the rear passenger-side wheel well. The definitive method is a smoke test, which will show smoke escaping from the canister body if it's leaking. Difficulty refueling is another strong symptom.
   Typical fix: Replace the charcoal canister assembly. This is accessible after removing the rear passenger-side wheel and fender liner.
   Est. part cost: $150-$300
3. Failed EVAP Purge Valve/Solenoid ⚪ Low Probability The purge valve controls the flow of vapors to the engine. If it gets stuck open, it can create a condition the computer interprets as a large leak. While not as common as the gas cap or canister, it's a known failure point in the EVAP system.
   How to confirm: The valve is located in the engine bay near the intake manifold. With the engine off, the valve should be closed. You can remove it 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 open and close to test its function.
   Typical fix: Replace the EVAP purge valve. The Mopar part number for the 2.0L engine is shared across the Giulia and Stelvio.
   Est. part cost: $50-$100
4. Cracked or Disconnected EVAP Hoses ⚪ Low Probability
   How to confirm: Visually inspect all accessible EVAP lines between the engine bay, the charcoal canister, and the fuel tank for obvious cracks, damage, or disconnections. 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 or reconnect it.
   Est. part cost: $10-$50

Rare But Worth Checking

• Damaged fuel filler neck
• Faulty fuel tank pressure sensor

Diagnosis Steps

1. Check the gas cap. Remove it, inspect the seal for damage, and reinstall it, tightening until it clicks at least three times. Clear the code with a scanner.
2. If the code returns, consider replacing just the gas cap's rubber seal, which is available from aftermarket suppliers like RKXtech, or replace the entire gas cap with a new OEM part. Clear the code and drive for a few days to see if the EVAP monitor runs and the light stays off.
3. If the light still returns, perform a thorough visual inspection of all visible EVAP hoses and components, especially around the charcoal canister in the rear passenger wheel well. Look for obvious cracks, damage, or disconnections.
4. The most effective next step is to have a professional (or use a DIY kit) perform a smoke test. This involves injecting low-pressure smoke into the EVAP system's service port and watching for where it escapes. This will pinpoint the exact location of the leak.
5. Based on the smoke test results, replace the leaking component. Forum experiences suggest the charcoal canister is a likely culprit if the gas cap is good.
6. If no leaks are found with a smoke test, investigate the purge and vent solenoids for proper electrical function using a multimeter or a bi-directional scan tool. The purge valve in the engine bay should be closed with the engine off.

Parts You'll Likely Need

• Fuel Tank Cap Seal (OEM #N/A (Seal is aftermarket, fits OEM cap 68313772AA)) — The rubber seal is a common failure point that causes a large leak. Replacing just the seal is a cost-effective first step.
  Trusted brands: RKX
  OEM price range: N/A
  Aftermarket price range: $10-$15
• Fuel Tank Cap (OEM #68313772AA) — This is the most frequent cause of a P0455 code due to a worn seal or improper tightening.
  Trusted brands: Mopar
  OEM price range: $30-$50
  Aftermarket price range: $15-$30
• Charcoal Canister (OEM #52109953AD (Verify with VIN)) — Forum discussions and dealer feedback indicate the canister on the Giulia can be prone to cracking or internal valve failure, causing a large leak that sets this code.
  Trusted brands: Mopar
  OEM price range: $200-$300
  Aftermarket price range: $150-$250
• Vapor Canister Purge Valve (OEM #05281586AB or 4627182AA (Verify with VIN)) — Can get stuck open, creating a constant vacuum leak in the EVAP system.
  Trusted brands: Mopar
  OEM price range: $65-$85
  Aftermarket price range: $40-$60

Related Codes That Often Appear With This One

• P0456 — This code indicates a small EVAP leak. If a small leak worsens over time, it can eventually trigger the P0455 for a large leak. Both codes point to the same system.
• P0442 — This code indicates a medium EVAP leak. Similar to P0456, it points to a leak in the same system, just of a different calibrated size.
• P2422 — This code for 'EVAP Vent Valve Stuck Closed' is often associated with a faulty charcoal canister assembly on the Giulia, as the valve is integrated with the canister.

Technical Service Bulletins (TSBs) & Recalls

• 18-027-20: Powertrain Control Module (PCM) Updates for various diagnostic improvements, including for P0455-00.
• 18-030-17: Powertrain Control Module (PCM) Updates for various diagnostic improvements, including for P0455-00. This TSB applies to 2.0L vehicles built on or before June 29, 2017.

Platform-Specific Known Issues

• The manufacturer has issued Technical Service Bulletins (TSBs) like #18-027-20 and #18-030-17 that include P0455 as one of several codes addressed by a PCM software update. If your vehicle is throwing this code and has never had this TSB performed, it may be worth checking with a dealer, especially if no physical leak is found.
• Real-world owner experiences frequently point to the charcoal canister as the root cause after the gas cap has been ruled out. One owner on Reddit noted their dealer service department sees a high failure rate for this part on the Giulia.
• Difficulty filling the fuel tank is a strong indicator that the EVAP canister/vent valve assembly has failed on this platform.

Scan Tool Commands That Help

• MultiECUScan: EVAP control valve opening (%) — To monitor the real-time operation of the EVAP purge valve. A user can connect to the engine ECU, graph this parameter, and rev the engine to see if the valve's opening percentage changes from 0%, confirming it is receiving commands and attempting to function.
• MultiECUScan: Actuation Tests (e.g., EVAP valve, fan) — To command specific components to turn on or off to test their function. Note: For 2017 and later models, a Security Gateway (SGW) bypass module is required to perform actuation tests. Without the bypass, the tool will connect but fail to execute commands with a 'Failed to Execute Status 13' error.

Wiring & Ground Locations

• EVAP Canister Electrical Connector — On the charcoal canister itself, located in the rear passenger-side wheel well, behind the fender liner.. This connector powers the integrated EVAP canister vent valve. It is crucial to ensure this is reconnected securely after replacing the canister to avoid immediately re-triggering an EVAP code.
• Battery Negative Terminal Quick Disconnect — In the trunk, on the negative post of the battery. It has a small button to press for release.. Disconnecting the battery for 15-30 minutes is a common procedure when working on the vehicle and can help reset electronic modules. It is required before working on many components. After reconnecting, a steering angle sensor reset procedure (turning the wheel lock-to-lock) is needed to clear dashboard warnings. This can sometimes clear temporary glitches but will not fix a permanent P0455 fault.

Real Owner Repair Stories

• YouTube user 'Club Alfa' (2018 Alfa Romeo Giulia Q4) — Check Engine Light with code P2422 (EVAP Vent Valve Stuck Closed), difficulty refueling (gas pump clicks off every few seconds).
  ❌ Tried (didn't work) The user went straight to replacing the canister based on the common symptoms and code P2422, which is often linked to P0455.
  ✅ What actually fixed it Replacing the entire charcoal canister assembly. The video documents the entire process, including accessing the part by removing the rear passenger wheel and fender liner, disconnecting the hoses and electrical connector, and installing the new part. After replacement and clearing the codes, the issue was resolved.
• Reddit user in /r/AlfaRomeo (2017 Giulia) — P0455 code for large EVAP leak.
  ❌ Tried (didn't work) Replacing the gas cap.
  ✅ What actually fixed it The issue was the charcoal canister. A user reported their dealer confirmed it's a high-failure-rate part and that their own car had required two replacements. This fixed the code after a new gas cap did not.

OEM Part Supersession History

• Unknown P/N for 2018 model canister → Updated canister design (e.g., part shown in 2022 video) — Design improvement. A video comparison shows the new part is lighter and has a different hose routing and an additional, separate canister component, suggesting the original design was flawed. The old part was visibly saturated with fuel/water residue, while the new part's filter element was clean and white.

Model Year Variations Within This Range

• 2017 (built on or before June 29, 2017): These earlier models are specifically called out in TSB #18-030-17 for a PCM software update to improve diagnostics for multiple codes, including P0455. This implies the software logic was changed for later 2017 and 2018 models.
• 2017+: Vehicles from 2017 onwards are equipped with a Security Gateway (SGW) module. This prevents unauthorized access to vehicle modules. To perform bi-directional controls (like commanding the purge valve open/closed) or PROXI alignment with tools like MultiECUScan, a physical SGW bypass harness must be installed.