DM-TL (Diagnosis Module - Tank Leakage)
The M54 engine with the Siemens MS43.0 engine control system uses the DMTL system for fuel system leakage monitoring. The pump is manufactured by Bosch for use with the Siemen's control system.
Scheme 1278
FUNCTIONAL OVERVIEW
The DM-TL is located in the drivers side rear wheel well in the X5 and next to the charcoal canister on the E46 - M54.
- In it's inactive state, filtered fresh air enters the evaporative system through the sprung open valve of the DM-TL.
- When the DME activates the DM-TL for leak testing, it first activates only the pump motor. This pumps air through a restrictor orifice (1.0 or 0.5 mm) which causes the electric motor to draw a specific amperage value. This value is equivalent to the size of the restrictor.
- The solenoid valve is then energized which seals the evap system and directs the pump output to pressurize the evap system.
The evap system is detected as having a large leak if the amperage value is not realized, a small leak if the same reference amperage is realized or no leak if the amperage value is higher than the reference amperage.
Scheme 1279
Leak Diagnosis Test Preconditions
The ECM only initiates a leak diagnosis test every second time the criteria are met. The criteria is as follows
- Engine OFF with ignition switched OFF.
- Engine Control Module still in active state or what is known as "follow up mode" (Main Relay energized, control module and DME components on-line for extended period after key off).
- Prior to Engine/Ignition switch OFF condition, vehicle must have been driven for a minimum of 20 minutes.
- Prior to minimum 20 minute drive, the vehicle must have been OFF for a minimum of 5 hours.
- Fuel Tank Capacity must be between 15 and 85% (safe approximation between 1/4 - 3/4 of a tank).
- Ambient Air Temperature between -7°C & 35°C (20°F & 95°F)
- Altitude < 2500m (8,202 feet).
- Battery Voltage between 11.5 and 14.5 Volts
When these criteria are satisfied every second time, the ECM will start the Fuel System Leak Diagnosis Test. The test will typically be carried out once a day i.e. once after driving to work in the morning, when driving home in the evening, the criteria are once again met but the test is not initiated. The following morning, the test will run again.
Test Results
The time duration varies between 45 & 270 seconds depending on the resulting leak diagnosis test results (developed tank pressure "amperage" / within a specific time period). However the chart below depicts the logic used to determine fuel system leaks.
