Mercury MerCruiser MCM 454 Mag MPI Service Manual page 702

SERVICE MANUAL NUMBER 23
Code 14 (2 of 3): Engine Coolant Temperature (ECT) Sensor Circuit
(Non-Scan)
TEST DESCRIPTION:
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 coolant sensor.
Step 3. This step will isolate the problem to CKT 410 (5 volt reference) or to the sensor
ground.
Step 6. Check the harness terminals thoroughly for loose connection. If the resistance or
the coolant sensor is monitored, the resistance should steadily decrease as the engine cool-
ant warms up. The resistance reading would stabilize when the thermostat opens.
Step 7. This step identifies if CKT 410 is open or shorted to ground.
IMPORTANT: If replacing the ECT, tighten hand tight plus 2-1/2 turns maximum.
Index
90-861326--1 MARCH 1999
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STEP
Was the "On-Board Diagnostic" (OBD) System
1
Check Performed?
2 1. Ignition OFF.
2. Disconnect ECT sensor connector.
3. Ignition ON, engine OFF.
4. Connect DVOM across coolant sensor
harness terminals.
Is voltage above 4 volts?
1. Connect positive DVOM lead from har-
3
ness terminal "B" CKT 410 (5 volt reference).
2. Connect negative DVOM lead to a good
ground (–) on engine.
Is voltage above 4 volts?
4 1. Remove DVOM.
2. Ignition ON.
3. Connect a test light to battery positive
(B+).
4. Touch test light to sensor harness termi-
nal "B" (CKT 410).
Is test light on?
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
ACTION VALUE YES NO
PROCEED TO
Go to
OBD
– Step 2
System
Check
Step 6 Step 3
Step 10 Step 4
Step 7 Step 5
Page 5F-5