Description And Operation: Operation

PURGE VALVE

The Powertrain Control Module (PCM) waits until the engine is running above 55°C (131°F) coolant temperature, with closed loop fueling system, before the purging process is activated. Under these conditions the engine should be running smoothly with no warm up enrichment. The purge valve duty (and flow) is initially ramped slowly because the vapor concentration is unknown and a sudden increase in purge could cause the engine to stall or loss of air fuel ratio control to occur. The concentration is then determined from the amount of adjustment that the closed loop fueling system is required to make to achieve the target air fuel ratio. Once the concentration has been determined, the purge flow can be increased and the injected fuel can be proactively adjusted to compensate for the known purge vapor and the target air fuel ratio control is maintained.

DIAGNOSTIC MODULE TANK LEAKAGE - NAS MARKET ONLY

To check the fuel tank and the EVAP system for leaks, the PCM operates the DMTL air pump and monitors the current draw. Initially, the PCM establishes a reference current by pumping air through the reference orifice and back to atmosphere. Once the reference current is determined, the PCM closes the changeover valve, which seals the EVAP system. The purge valve remains de-energized and is therefore closed. The output from the air pump is diverted from the reference orifice and into the EVAP system.

Providing there are no leaks, the air pump will begin to pressurize the EVAP system and the load and current draw of the air pump motor increases. By monitoring the rate and level of the current increase, the PCM can determine if there is a leak in the EVAP system.

During normal vehicle operation, 15 seconds after the engine has started, the PCM energizes the heating element in the pump to prevent condensation formation and possible incorrect readings. The heater remains energized until either the engine or ignition are off (if no DMTL test is running) or until after the DMTL test is completed.

Leaks are classified as:

Minor - equivalent to a hole diameter of 0.5 to 1.0 mm (0.02 to 0.04 in)
Major - equivalent to a hole diameter of 1.0 mm (0.04 in) or greater.

The PCM performs a check for major leaks each time the ignition is switched off, providing the following conditions are met:

The vehicle speed is zero.
The engine speed is zero.
The pressure altitude (70 kPa (10.15 lbf/in² ) derived from engine load calculations) is below 3047 m (10000 feet).
The ambient temperature is between 0 and 40°C (32 and 104°F).
The evaporative emission canister vapor concentration factor is less than 3 (where 0 is no fuel vapor, 1 is stoichiometric fuel vapor and greater than 1 is rich fuel vapor).
The fuel tank level is valid and between 15 and 85% of nominal capacity.
The battery voltage is between 11 and 16 V.
The last engine running time was more than 10 minutes (to ensure any moisture within the DMTL pump has been removed).
During the last engine start the difference between engine coolant temperature and ambient air temperature was less than 7°C (13°F).
No errors are detected with the EVAP system components, the ambient air temperature and the fuel level.
High range is selected on the transfer case.

NOTE: A leak test can be performed using the Land Rover approved diagnostic equipment. This overrides the above conditions and is useful for checking correct system and component operation.

The PCM performs a check for minor leaks after every 2nd major leak check.

When the leak check is complete, the PCM stops the DMTL pump and opens (de-energizes) the changeover valve.

If the fuel filler cap is opened or refueling is detected during the leak check, by a sudden drop in the current draw or a rise in the fuel level, the PCM aborts the leak check.

If a leak is detected during the check, the PCM stores an appropriate fault code in its memory. If a leak is detected on two consecutive checks, the PCM sends signals to the Body Control Module/Gateway Module (BCM/GWM) assembly via FlexRay and the BCM/GWM transmits the signals to the Instrument Cluster (IC) via High Speed (HS) Controller Area Network (CAN) comfort systems bus. The IC illuminates the Malfunction Indicator Lamp (MIL) on the next drive cycle.

The duration of a leak check can be between 60 and 900 seconds depending on the test results (developed tank pressure amperage within a specific time period) and fuel tank level.