Coolant Temperature Warning - Volvo D1-13 B Workshop Manual

Group 30: Electrical system Malfunctions

Coolant temperature warning

Fault indication
Tachometer:
The tachometer LCD screen will show a flashing cool-
ant temperature icon and the alarm buzzer sounds.
Alarm display:
The coolant temperature indication flashes in the
alarm display + audible warning.
Circuit description
The coolant temperature sensor consists of a ther-
mistor. The property of a thermistor is that its resis-
tance changes non-linearly with temperature in the
medium it measures. Pin 5 in the engine interface
Coolant temperature
connector at the MDI supplies the thermistor with a
reference voltage of +5 Volt. The sensor is connected
to battery negative via the engine. When the engine
coolant is cold, the sensor resistance is high and the
MDI senses a voltage close to the reference level.
When the coolant heats up, the resistance in the ther-
mistor falls and the voltage drop across the thermistor
changes.
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