1 Solenoid (in tank flap)
2 Tank flap switch (reed contact)
The tank flap switch is incorporated into the fuel filler neck insert. The actuating solenoid is located in a bracket on the tank flap. The tank flap switch is a reed contact and informs the fuel additive control unit that the fuel tank is filled. However, the fuel additive control unit only registers that refueling has taken place if detected by the fuel level sensor in addition to the tank flap switch signal and if the vehicle is traveling at a speed of < 3 km/h. If a clear signal is received from the tank flap switch as a result of opening and closing the tank flap and if an increase in the fuel quantity (differential quantity) of at least 5 liters is detected in the fuel tank once the ignition has been turned on, the fuel additive control unit assumes that refueling has taken place. The fuel additive control unit calculates the fuel additive quantity to be injected, according to the differential quantity calculated, and activates the fuel additive pump. Activation/metering is performed as soon as the vehicle exceeds a speed of 40 km/h or, if this speed is not reached, 4 minutes after the engine is first started. Note: After the fuel additive tank has been topped up (during scheduled service) the counter in the fuel additive control unit must be reset. It can be reset by opening and closing the tank flap in a certain way and use should be made of this feature (see current Service Literature). Resetting the counter via the tank flap switch is not possible if either the engine system error warning lamp or the MIL has illuminated as a result of the fuel additive tank becoming empty. In this case, the counter must be reset using the WDS. When the tank flap is closed, the tank flap switch is open. Effects of faults If the signal from the tank flap switch fails, small refueling quantities (below 10 liters) cannot be detected. The software on the fuel additive control unit has been designed to only allow fuel additive to be injected in the case of a missing signal from the tank flap switch if the refueling quantity is at least 10 liters. The reason for this is that, in the worst case scenario, the vehicle may, for example, have been rolled onto a slope with the " ignition OFF". Then, when the ignition is next switched on, the fuel additive control unit could register an increased quantity of fuel via the fuel level sensor and might misinterpret this as a refueling operation. To prevent fuel additive from being injected unnecessarily, if the tank flap switch is faulty, the fuel level difference is increased from at least 5 liters to a minimum of 10 liters. If the signal fails, the engine system error warning lamp is actuated.
