Fuel Tank Pressure/Leak Detection Sensor: 7-Series
- Evaporative leakage detection is performed on fuel storage system by Tank Leakage Diagnostic Module (DM-TL) pump which contains an integral DC motor that is activated by ECM. ECM monitors pump motor operating current as the measurement for detecting leaks. DM-TL generates a pressure of.29-.43 psi (20-30 mbar) in the fuel tank and evaporative system. Electrical current required for this is calculated by ECM and serves as the indirect value for the tank pressure. The DM-TL carries out a reference measurement before each measurement. This is performed by building up a pressure for 10-15 seconds using an internal orifice of.019" (.5 mm) as a reference and ECM monitors current (20-30 mA) required by pump motor.
- If a lower pressure is detected in pressure build-up (low current draw) as compared to reference measurement, this indicates a leak in fuel tank/evaporative system. If a higher pressure is detected (higher current draw), the system does not have a leak. The pump also contains an ECM controlled change over valve that is energized closed during a leak diagnosis test. The ECM only initiates a leak diagnosis test every second time the criteria is met. The criteria is as follows:
- Engine off with ignition off.
- ECM still in active state or what is known as "follow up mode". (ECM relay energized, ECM and components online 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, vehicle must have been off a minimum of 5 hours.
- No faults in ECM for DM-TL/tank venting system.
- Fuel tank capacity must be between 10-90 percent (safe approximation between 1/4-3/4 of a tank).
- Ambient air temperature between 19-95°F (-7-35°C).
- Altitude less than 8202 feet.
- Battery voltage between 11.5-14.5 volts.
- When these criteria are satisfied every second time, ECM will start FUEL SYSTEM LEAK DIAGNOSIS TEST. Test will typically be carried out once a day. The following morning, the test will run again.