Mercury MerCruiser MCM 454 Mag MPI Service Manual page 752

SERVICE MANUAL NUMBER 23
Code 15 (2 of 3): Engine Coolant Temperature (ECT) Sensor Circuit
(Non-Scan) High Temperature Indicated
DIAGNOSTIC AIDS:
Check for the following conditions:
After repairs, clear DTC's following "Clearing Trouble Codes" procedure at the front of this
section. Failure to do so may result in DTC's not properly being cleared.
TEST DESCRIPTION:
IMPORTANT: If replacing the ECT sensor, tighten hand tight plus 2-1/2 turns maxi-
mum.
Index
90-861326--1 MARCH 1999
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Poor connection at ECM. Inspect harness connectors for backed out terminals,
improper mating, broken locks, improperly formed or damaged terminals, and poor ter-
minal to wire connection.
Damaged harness. Inspect the wiring harness for damage. If the harness appears to be
OK, observe the ECT display on the scan tool while moving connectors and wiring har-
nesses related to the ECT sensor. A change in the ECT display will indicate the location
of the fault.
Check harness routing for a potential short to ground in CKT 410.
Number(s) below refer to circled number(s) on the diagnostic chart.
Step 2. This step checks if there is a problem with the ECM and wiring or if the problem
is the ECT sensor.
Step 3. Check the harness terminals thoroughly for loose connections. If the resistance
of the ECT sensor is monitored, the resistance should steadily decrease as the engine
coolant warms up. The resistance reading should stabilize when the thermostat opens.
STEP
Was the "On-Board Diagnostic" (OBD) System
1
Check Performed?
2 1. Ignition "OFF."
2. Disconnect ECT sensor harness terminals.
3. Ignition "ON," engine "OFF."
4. Connect DVOM across the coolant sensor
harness terminals.
Is voltage above the specified value?
ACTION
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
VALUE YES
PROCEED TO
– Step 2
4 Volts Step 3
NO
Go to
OBD
System
Check
Step 4
Page 5G-7