Determination of coolant temperature, function

W07.16-1207-81

General

The coolant temperature which is required for a number of factors, including fan regulation or computation of the start of actuation of fuel injectors, is determined by the engine management (MCM) control unit (A4).

For fan regulation the engine management (MCM) control unit (A4) uses measurements made by the coolant intake temperature sensor (B607) and the coolant outlet temperature sensor (B606).

For determining the start of actuation and the duration of actuation (injection quantity) of the fuel injector for cylinder 1 (Y608), fuel injector for cylinder 2 (Y609), fuel injector for cylinder 3 (Y610), fuel injector for cylinder 4 (Y611), fuel injector for cylinder 5 (Y612), and fuel injector for cylinder 6 (Y613), the engine management (MCM) control unit (A4) uses exclusively the measurement values of the exhaust coolant temperature sensor (B606).

Function

A temperature-dependent resistance with a negative temperature coefficient (NTC) is located in the intake coolant temperature sensor (B607) and in the exhaust coolant temperature sensor (B606) in each case, i.e. an electrical resistance that decreases as the temperature increases.

Depending on the temperature of the coolant at the coolant intake temperature sensor (B607) or coolant outlet temperature sensor (B606), the voltage applied to the engine management (MCM) control unit (A4) changes. Based on this, the intake or outlet coolant temperature is determined.

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.