The voltage for the preheater plugs is supplied via the preheater relay. The relay is switched by the DDE control unit.
The preheater plugs are designed as sheathed element preheater plug and equipped with a new plug connection. They are connected in parallel.
The preheating duration is dependent on the engine coolant temperature and battery voltage and is indicated by the preheating/DDE indicator.
Preheating takes place for approx. 2 seconds between 6 °C and 20 °C. No preheating takes place at temperatures above this value.
After-heating takes place after engine start at temperatures below 40 °C in order to improve idle and exhaust characteristics.
The DDE control unit receives a fault signal from the preheater relay in the form of the S_GRS signal if there is a fault in the preheater plugs, preheater relay or in the voltage supply of the relay. The DDE control unit itself detects a short-circuit/open-circuit in the relay activation function. Fault code 8 "preheating system" is stored in both cases.