Circuit description
The
coolant
temperature sensor consists of a thermis-
tor which forms a closed circuit with an internal resistor
in the engine control unit (EMS2). The thermistor resis-
tor changes in a non-linear manner, depending on the
coolant temperature. The EMS2 provides the circuit
with a reference voltage of +5 Volt. The EMS2 meas-
ures the voltage drop over the thermistor via pin 27 and
pin 18 on the EMS2. Pin 1 on the sensor is connected
to battery negative via pin 18 on the EMS2. When the
coolant is cold, the thermistor resistance is high and
the EMS2 senses a high voltage drop. As the coolant
warms up, the resistance in the thermistor falls and the
voltage drop across it falls.
Please refer to the table, “resistance/temperature” in
this fault code chapter.
Measurements
Checking signal cable, coolant temperature
switch page 169
Checking negative cable, coolant temperature
switch page 170
Checking coolant temperature sensor page 156
Checking the sensor cable for open circuit or
shortcircuit page 157
b
a
GR / W
P0007217
a Coolant temperature
b Connector B
30-2 Fault Tracing
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