Diagnostic Module Tank Leakage (DMTL) Pump - NAS Only

WARNING: This page is about a different car, the 2019 Jaguar XJ and 2018 Jaguar XJ. However, it is still accessible from the selected car via links, so may be relevant.

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

The DMTL test is performed after the engine has stopped following an engine running period of more than 10 minutes. The fuel tank must be between 15% and 85% full, the ambient temperature must be above 0°C (32°F) and less than 40°C (104°F) and the vehicle has not been started for at least 180 minutes before the last engine start.

With the change-over valve and the purge valve closed, the load on the air pump falls to zero. Providing there are no leaks, the air pump will begin to pressurize the EVAP system and the load and current draw in the pump motor increases. By monitoring the rate and level of the current increase, the ECM can determine if there are leaks in the EVAP system.

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

Leaks are classified as follows:

Minor - equivalent to a hole diameter of 0.5 to 1.0 mm (0.02 to 0.04 inch)
Major - equivalent to a hole diameter of 1.00 mm (0.04 inch) or greater.

The ECM 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 atmospheric pressure is above 70 KPa (10.15 lbf/in² ), for example the altitude is less than approximately 3047 m (10000 feet)
The ambient temperature is between 0 and 40°C (32 and 104°F)
The Evaporative emissions canister vapor concentration factor is 5 or less (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 engine running time during the previous engine cycle was more than 10 minutes
The battery voltage is between 10 and 15 volts
The last engine off time was more than 180 minutes
No errors are detected with the EVAP system components, the ambient air temperature and the fuel level.

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

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

When a leak check is complete, the ECM stops the DMTL pump and opens (de-energizes) the change over valve.

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

If a leak is detected during the check, the ECM stores an appropriate fault code in it memory. If a leak is detected on two consecutive checks, the ECM will illuminate the Malfunction Indicator Lamp (MIL) in the Instrument Cluster (IC) on the next drive cycle.

The duration of a leak check can be between 60 and 900 seconds, depending on the results and the fuel tank level.

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

The DMTL pump periodically checks the EVAP system and the fuel tank for leaks when the ignition is off. The DMTL system comprises the purge valve and the Evaporative emissions canister, with the addition of the DMTL pump and intake DMTL filter.

The DMTL pump is located at one end of the Evaporative emissions canister and is connected to the canister atmospheric vent. The pump comprises an electric air pump, a Positive Temperature Coefficient (PTC) heating element, a normally open change-over valve and a reference orifice.

The DMTL pump is only operated when the ignition is off and is controlled by the ECM. The ECM also monitors the air pump operation and the change-over valve for faults.

The DMTL filter is located on the fuel filler pipe and is connected to the DMTL pump via a pipe. The DMTL filter protects the DMTL pump from dust being drawn into the system when the pump is operating.

The DMTL pump is operated to pressurize the fuel tank and the fuel vapor system and the ECM measures the current change with the change-over valve in different states. The ECM makes a comparison of the current draw in each state and any difference indicates the degree of any leakage. If a leak is detected, the ECM will set an appropriate Diagnostic Trouble Code (DTC).