If there is a malfunction in the preheating system of the diesel Ford Mondeo III, the fuse shall be checked first, in particular the safety of the on-board power supply.
Also, with the help of a multimeter check the voltage in the incandes-must be at least 11.5 V, otherwise the candles need to be replaced. To test the voltage, disconnect the wire of one of the four filament lamps. Attach a reference lamp between the mass and the corresponding connecting wire. Detach the coolant temperature sensor. Set the ignition key to the "Preheat" position. If the control lamp is lit for 20 seconds, the voltage on the filament lamps is present and the heating time set by the control device is correct. If the control lamp does not catch up, check the main fuse or the preheating relay. If the time of the filament is smaller, then the control unit is likely to be malfunctioning.
