Mercury MerCruiser MCM 454 Mag MPI Service Manual page 718

SERVICE MANUAL NUMBER 23
Diagnostic Testing Using A Scan Tool (Scan)
Code 14 (1 of 2): Engine Coolant Temperature (ECT) Sensor Circuit (Scan)
CIRCUIT DESCRIPTION:
The Engine Coolant Temperature (ECT) Sensor uses a thermistor to control the signal volt-
age to the ECM. The ECM applies a voltage on CKT 410 to the sensor. When the engine
coolant is cold, the sensor (thermistor) resistance is high, therefore, the ECM will see high
signal voltage. As the engine coolant warms, the sensor resistance becomes less, and the
voltage drops. At normal engine operating temperature, 160-180 F (71-82 C), the voltage
will measure about 1.5 to 2.0 volts.
DIAGNOSTIC AIDS:
Check harness routing for a potential short to ground in CKT 410.
Scan tool displays engine temperature in degrees Fahrenheit and Celsius. After engine is
started, the temperature should rise steadily, reach normal operating temperature, and then
stabilize when thermostat opens.
See "Intermittents" in "Troubleshooting."
An intermittent problem may be caused by a poor or corroded connection, rubbed through
wire connection, a wire that is broken inside the insulation, or a corroded wire.
Any circuitry that is suspected as causing the intermittent complaint should be thoroughly
checked for backed-out terminals, improper mating, broken locks, improperly formed or
damaged terminals, poor terminal-to-wiring connections, corroded terminals and/or wiring,
or physical damage to the wiring harness. After repairs, clear codes following "Clearing
Codes" at the front of this section. Failure to do so may result in codes not properly being
cleared.
Index
90-861326--1 MARCH 1999
Downloaded from https://needmanual.com/
a - Engine Coolant Temperature (ECT) Sensor
b - To Map Sensor
c - Engine Coolant Temperature (ECT)
d - Sensor Ground
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
a
b
c
d
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