Engine cooling DDE7

Coolant-temperature sensor

The coolant-temperature sensor is bolted to the front of the cylinder head and it picks up the coolant temperature via its changeable resistance.

The coolant temperature serves as a measured variable for the following functions:

• Exhaust-gas recirculation
  
• Fuel injection rate calculation
  
• Control condition for air conditioning system
  
• Radiator shutter control condition
  
• Electric auxiliary heater control condition
  
• Charge-air-pressure control
  
• Glow-period control
  
• Activation of electric fan
  
• Swirl flap activation
  
• Idle speed control
  
• Rail pressure control
  

Electric fan

The DDE control unit activates the electric fan by means of a square-wave signal with a pulse duty factor of between 5 % and 95 %, thus activating various speeds at the electric fan. The electric fan features its own positive and earth supply.

Radiator shutter

The DDE control unit opens or closes the radiator blind depending on the operating range.

The radiator blind opens at:

• Coolant temperature > 100 °C (closes at < 95 °C)
  
• Speed > 180 kph (closes at < 140 km/h)
  
• Speed request for electric fan > 1600 rpm (closes at < 1380 rpm)
  
• Speed request for electric fan by air conditioning system > 1600 rpm
  (closes at < 1050 rpm)
  
• Winter safety function:
  
  • Window wipers ON and
    
  • Speed between 65 kph and 125 kph and
    
  • Ambient temperature between -8 °C and 2 °C
    
• Electric fan after-run
  
• With automatic transmission: transmission temperature > 115 °C (closes at < 110 °C)
  

During trailer towing, the radiator blind is permanently opened if the trailer is connected to the trailer module.

The winter safety function prevents the radiator blind from freezing shut while the vehicle is being driven in wet or snowy conditions.

Notes for Service department

Diagnosis instructions

Coolant temperature sensor

The coolant-temperature sensor is destroyed in the case of short circuit to positive.

Target values for resistance check:

• Resistance at 20 °C: 2.5 - 3.0 kOhm
  
• Resistance at 50 °C: 0.7 - 0.9 kOhm
  
• Resistance at 100 °C: 0.12 - 0.17 kOhm