MG ZS (Gen2) P0455 EVAP System Large Leak Detected

The P0455 EVAP System Large Leak Detected fault indicates that the engine control module (ECM) has identified a significant leak within the Evaporative Emission Control (EVAP) system. During self-diagnostic leak tests, the ECM seals the EVAP system and monitors fuel tank pressure. If the system is unable to maintain the required pressure because of a large leak or disconnected component, the ECM stores DTC P0455. This fault applies to the MG ZS Gen2 (ZS11 platform), introduced from 2024 onwards.

Symptoms

  • Check Engine Light illuminated
  • Strong fuel vapour smell around the vehicle
  • Increased evaporative emissions
  • Failed emissions inspection
  • Slight reduction in fuel economy
  • No noticeable drivability concerns in most cases
  • Additional EVAP-related fault codes may be present

Possible Causes

  • Loose, missing, or damaged fuel filler cap
  • Disconnected, split, or broken EVAP hose
  • Cracked charcoal canister
  • Faulty EVAP purge control valve
  • Faulty EVAP vent control valve
  • Damaged fuel tank or filler neck
  • Leaking fuel tank pressure sensor seal
  • Damaged EVAP canister connections
  • Wiring or electrical connector faults
  • Engine control module (ECM) fault (rare)

Diagnosis

Diagnosis begins by confirming the stored fault code and reviewing freeze-frame data using a compatible diagnostic scan tool. The fuel filler cap should be inspected first, followed by a thorough visual inspection of all EVAP hoses, vapour lines, the charcoal canister, purge valve, vent valve, and fuel tank connections. A smoke machine is typically used to quickly identify the location of a large leak, while live fuel tank pressure sensor data should be analysed to verify correct system operation. Manufacturer diagnostic procedures may also include electrical testing of the EVAP valves and leak testing of individual system components.

For vehicles operating in New Zealand, following OEM diagnostic procedures ensures the actual source of the leak is identified before replacing EVAP components, reducing unnecessary repair costs.

Accurately diagnosing this fault often requires manufacturer testing procedures, wiring diagrams, connector pinouts, EVAP system schematics, smoke testing procedures, fuel tank pressure sensor specifications, and system calibration information. Access to the factory service manual significantly reduces diagnostic time and helps prevent unnecessary parts replacement.

Applicable Years

2024, 2025, 2026, onwards

To order the correct OEM Service and Repair Manual for your MG ZS, submit your request using the form below, and our team will provide the ordering details.