Mercury MerCruiser MCM 454 Mag MPI Service Manual page 750

SERVICE MANUAL NUMBER 23
Code 14 (2 of 3): Engine Coolant Temperature (ECT) Sensor Circuit
(Non-Scan) Low Temperature Indicated
TEST DESCRIPTION:
Index
90-861326--1 MARCH 1999
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Number(s) below refer to step number(s) on the diagnostic table.
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. This step will isolate the problem to CKT 410 (5 volt reference) or to CKT 814
(sensor ground).
Step 4. 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?
1. Connect positive (+) DVOM lead to harness
3
terminal "B" CKT 410 (5 volt reference).
2. Connect negative (–) DVOM lead to a
known good ground.
Is voltage above the specified value?
Locate and repair intermittent faulty connec-
4 tions. If OK, replace faulty ECT sensor. Is
action complete?
Locate and repair open CKT 410. If a problem
5
is found repair as necessary. Was a problem
found?
Locate and repair open ground CKT 814. If a
6
problem is found, repair as necessary. Was a
problem found?
Repair faulty ECM connections or replace
7
faulty ECM. Is action complete?
ACTION
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
VALUE YES
PROCEED TO
– Step 2
4 Volts Step 4
4 Volts Step 6
–
–
Verify
Re air Repair
–
–
NO
Go to
OBD
System
Check
Step 3
Step 5
–
Ste 7 Step 7
–
Page 5G-5