Preheating System DDE 4.1

Voltage is supplied to the preheater plugs via two preheater relays. Both relays are activated by the DDE master control unit.

The heater plugs are designed as sheathed-element glow plugs. The cylinders are allocated to the two relays as follows:

Preheater time control

The preheating duration is dependent on the coolant temperature and battery voltage and is indicated by the preheater/DDE indicator.

Preheating

At temperatures below 5 °C, preheating takes place for at least 4 seconds. The preheating time increases as the temperature decreases.

After-heating

After engine start, after-heating takes place at a temperature below 51 °C in order to improve idling and exhaust gas characteristics. The duration is dependent on the characteristic curve, e.g. 80 s after-heating at 20 °C.

Start preheating

If, after the preheating time has elapsed, the engine is not started and the ignition remains switched on, start preheating takes place for a maximum of 6 seconds.

Troubleshooting

The master DDE control unit itself detects a short/break in relay activation (type of fault "activation short-circuit ...", "activation break ..."). If there is a defect in the preheater plugs, a preheater relay or in the voltage supply of a preheater relay, the DDE master control unit receives an error message via the S_GRS1 or S_GRS2 signals from the respective preheater relay (type of fault "preheater system fault"). In the event of a defect, fault codes 3505 "preheating system 1" or 3506 "preheating system 2" are stored.