MG ZS (Gen2) P0456 EVAP System Very Small Leak Detected

The P0456 EVAP System Very Small Leak Detected fault indicates that the engine control module (ECM) has detected a very small leak within the Evaporative Emission Control (EVAP) system. During scheduled self-tests, the ECM seals the EVAP system and monitors fuel tank pressure over a specified period. If a slight pressure loss exceeding the manufacturer’s threshold is detected, indicating a very small vapour leak, the ECM stores DTC P0456. This fault applies to the MG ZS Gen2 (ZS11 platform), introduced from 2024 onwards.

Symptoms

  • Check Engine Light illuminated
  • Slight fuel vapour smell around the vehicle
  • Increased evaporative emissions
  • Failed emissions inspection
  • Little or no noticeable change in engine performance
  • Slight reduction in fuel economy (occasionally)
  • Additional EVAP-related fault codes may be present

Possible Causes

  • Loose or improperly tightened fuel filler cap
  • Worn or damaged fuel cap seal
  • Hairline crack in an EVAP hose
  • Minor leak in the charcoal canister
  • Slight leak from the EVAP purge control valve
  • Faulty EVAP vent control valve
  • Small leak at an EVAP hose connection or fitting
  • Fuel tank pressure sensor fault
  • Damaged wiring or electrical connectors
  • 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 and seal should be inspected first, followed by a careful examination of the EVAP hoses, fittings, charcoal canister, purge valve, and vent valve for signs of very small leaks. Because leaks associated with P0456 are often too small to identify visually, a smoke machine is typically required to accurately locate the leak. Live data from the fuel tank pressure sensor should also be analysed to verify proper system operation. Manufacturer diagnostic procedures may include smoke testing, pressure decay testing, and electrical testing of the EVAP system components.

For vehicles operating in New Zealand, following OEM diagnostic procedures helps accurately identify very small EVAP leaks while avoiding unnecessary replacement of fuel system or emissions components.

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.