EDI DIAGNOSIS SERVICE MANUAL NUMBER 22
Page 5E-22 90-860074--1 FEBRUARY 2002
ECT (Engine Coolant Temperature) Sensor
Scan Code: P0115
Blink Code: 1113
Malfunction Indicator Lamp: ON
33
14
1
2
BRN/PUR
33
14
75341
WHT/BRN
a
b
c
d
f
e
a-ECT Sensor
b-ECT Connector
c-ECT Signal
d-5 Volt Reference Signal
e-Sensor Ground
f-To Injection Pump
CIRCUIT DESCRIPTION:
The ECT (Engine Coolant Temperature) Sensor is a thermistor (a resistor which changes
value based on temperature) immersed in the engine coolant stream. Low coolant
temperature produces a high resistance, while high temperature causes low resistance.
The ECM supplies a 5 volt signal to the ECT through a resistor in the ECM and measures
the voltage. The voltage will be high when the engine is cold, and low when the engine is
hot. By measuring the voltage, the ECM knows the engine coolant temperature. Engine
coolant temperature affects most systems the ECM controls. The voltage received at the
ECM will determine operation of the fuel timing solenoid and glow plug relays.
A failure in the ECT circuit should set Scan Code P0115. Remember, this code indicates a
failure in the coolant temperature sensor circuit, so proper use of the test description
information will lead to either repairing a wiring problem or replacing the sensor.
CKT PIN
NAME
14 Engine Coolant Temperature Sensor Signal
33 Sensor Ground (–)
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