What does the P0455 OBD-II code mean?

The P0455 code indicates a large leak explicitly in the evaporative emission control (EVAP) system. The purpose of the EVAP system is to prevent fuel vapours from escaping into the atmosphere, so when the P0455 triggers, the most common reason for this is a broken, loose or missing gas cap. The P0440 OBD-II code is a general code for a less severe leak with the EVAP system.

How serious is the P0455 code?

This diagnostic code is not considered serious, and the driver is unlikely to notice any symptoms associated with this code other than the Check Engine light illuminating. However, if fuel odours are powerful, indicating a leak, getting your vehicle booked in for repair as soon as possible is advisable, as an EVAP system leak can cause decreased fuel economy in some circumstances.

What are the common symptoms of a P0455 trouble code?

Indications of an EVAP system leak are limited. However, the most common P0455 trouble code symptoms are:

  • Check Engine Light illuminated
  • Strong fuel odour
  • Excessive fuel consumption

What are the causes of a P0455 diagnostic code?

The most common causes for the P0455 trouble code triggering are:

  • Loose, damaged or missing fuel filler cap (most common)
  • Hose leak, particularly on the breather system and connecting hose to the filler neck to the fuel tank
  • Defective or stuck EVAP vent control valve
  • Defective or stuck EVAP purge volume control valve
  • Damaged charcoal canister /filter (certain vehicles only)

How to diagnose a P0455 OBD-II code?

The simplest way to diagnose an OBD-II trouble code is to use an OBD-II scanner or book a diagnostic check with a trusted mechanic or garage. Following the diagnostic steps fully and correctly is essential for accurate diagnosis. This is particularly important with older vehicles with over 100,000 miles, which can experience momentary sensor problems. If the car appears to operate normally with an illuminated check engine light, the OBD-II system should be reset before additional work or repairs are performed. 

    • Scan your system for other OBD-II codes. If present, these must be resolved first before proceeding
    • Clear the fault codes and follow up with a test drive of the car while reading the live data on an OBD-II scanner
    • If the code persists, inspect the gas cap for damage or problems with the seal
    • Make a visual inspection for obvious leaks


  • Perform a smoke test of the EVAP system to look for leaks 
  • Perform electrical testing of the purge and vent control valves for defects


How to fix a P0455 OBD-II trouble code?

It is recommended to test drive the vehicle after each check/work is actioned to see if the fault code clears. If the code returns, move on to the next repair. The most common repairs to resolve a P0455 are:

  • Verify the code with an OBD-II scanner, and reset the fault code. Follow this with a test drive of the car to see if the trouble code clears. If it returns: 
  • Replace the gas cap if it or the seal is damaged or doesn’t tighten 
  • Replace the fuel filler neck i