5.3.1 Description

Fig 1: Identifying Evaporative Emission System Monitoring Description

Courtesy of LAND ROVER NORTH AMERICA, INC.

The evaporative emission monitoring system permits the detection of leaks with a diameter of 0.020" or greater.

This is achieved by means of a pressure test of the system. This is performed by the DMTL, which is an electrically operated pump fitted to the atmospheric air intake of the EVAP canister. This unit contains an electric heater to prevent condensate formation, though the ECM contains functionality to inhibit the leak check if humidity is detected. If humidity is detected on more than a tunable number of test attempts, then the system assumes that there is a fault present.

The test proceeds in 2 stages: -

• Reference Leak Measurement - The pump operates against the reference restriction within the DMTL. The ECM measures the current consumption of the pump motor during this phase.
• Leak Measurement (see diagram below) - The solenoid in the DMTL is operated in order to shut off normal purge airflow into the EVAP canister. The pump can now pressurize the fuel tank and vapor handling system. The ECM again measures the current consumed by the pump motor and by comparing this with the reference current, determines if a leak is present or not. A high current indicates a tight system and a low current indicates a leaking system.
  Fig 2: Identifying Leak Measurement

  Courtesy of LAND ROVER NORTH AMERICA, INC.
  Fig 3: Pump Current And Time Graph

  Courtesy of LAND ROVER NORTH AMERICA, INC.