Mercury MerCruiser MCM 454 Mag MPI Service Manual page 751

TROUBLE CODE DIAGNOSTICS - 7.4L MPI
Code 14 (3 of 3): Engine Coolant Temperature (ECT) Sensor Circuit
(Non-Scan) Low Temperature Indicated
ENGINE COOLANT TEMPERATURE SENSOR CHART
Code 15 (1 of 3): Engine Coolant Temperature (ECT) Sensor Circuit
(Non-Scan) High Temperature Indicated
CIRCUIT DESCRIPTION:
The Engine Coolant Temperature (ECT) sensor uses a thermistor to control the signal
voltage to the ECM. The ECM applies 5 volts on CKT 410 to the sensor. When the engine
coolant is cold, the sensor (thermistor) resistance is high. As the engine coolant warms up,
the sensor resistance becomes less. see engine coolant temperature sensor chart under
"Diagnostic Aids." At normal operating temperature 160 F-180 F (71 C-82 C), the voltage
will measure about 1.5-2.0 volts.
Index
Page 5G-6
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Temperature - to - Resistance Values (Approximate)
F
210
160
100
70
40
20
0
-40
a
a - Engine Coolant Temperature (ECT) Sensor
b - To Map Sensor
c - Engine Coolant Temperature (ECT)
d - Sensor Ground
ECT Sensor
C
100
70
38
20
4
-7
-18
-40
b
SERVICE MANUAL NUMBER 23
OHMS
185
450
1,800
3,400
7,500
13,500
25,000
100,700
c
d
90-861326--1 MARCH 1999