Determination of coolant temperature, function

W07.16-1146-76

General

The coolant temperature is, amongst other things, needed for fan control and for computation of the actuation begin as well as the actuation period (=injection quantity) of the fuel injectors.

Function

The coolant temperature is determined by the engine management (MCM) control unit (A4) based on measurements of the coolant outlet temperature sensor (B606). There is a temperature-dependent resistance with a negative temperature coefficient (NTC) in the coolant outlet temperature sensor (B606) – that is an electrical resistance which reduces with increasing temperature. The voltage applied to the engine management (MCM) control unit (A4) changes according to the temperature of the coolant; the level of this voltage is what determines the coolant temperature.

 If one of the sensors fails the engine management (MCM) control unit (A4) continues to operate with substitute values. This allows the engine to be started even under unfavorable conditions and for the vehicle to continue to be driven.
The engine management (MCM) control unit (A4) will limit the specified engine torque to protect the engine from overheating if the coolant temperature reaches an impermissibly high value.