Mercury MerCruiser MCM 454 Mag MPI Service Manual page 692

SERVICE MANUAL NUMBER 23
Discrete Input Circuit Check - Non-Scan 7.4L MPI Only (2 of 5)
NOTE: The ECM should only be replaced after all switches and circuits have been tested
and found to be functioning properly.
TESTING BUZZER
TESTING OIL PRESSURE SWITCH
Index
90-861326--1 MARCH 1999
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STEP
1 1. Key "ON", Engine "OFF".
Does buzzer sound?
2 1. Start engine.
Does buzzer sound?
1. Disconnect TAN/BLU wire at buzzer.
3
2. Key "ON", Engine "OFF".
3. Touch TAN/BLU wire to ground (–).
Does buzzer sound?
Buzzer is working properly. Proceed to "Testing
4
Switches" or "Testing Circuits".
Check to ensure that there is battery power (+)
to the PUR wire going to buzzer. If there is,
5
replace buzzer and verify repair
(Starting at Step 1).
Discrete switches may all be functioning prop-
erly.
6
Proceed to check all discrete circuits to verify
each works properly.
STEP
1. Disconnect PUR wire from oil pressure
switch.
1
2. Engine "OFF".
3. Check for continuity between terminal on
switch and ground (–).
Is there continuity?
1. Start engine.
2
2. Check for continuity between terminal on
switch and ground (–).
Is there continuity?
3 Replace oil pressure switch. Verify repair.
4 Oil pressure switch is working properly.
ACTION
ACTION
GENERAL SYSTEM DIAGNOSTICS
VALUE YES NO
PROCEED TO
Step 2 Step 3
Step 6 Step 4
Step 4 Step 5
–
–
–
VALUE YES NO
PROCEED TO
0 Ohms Step 2 Step 3
0 Ohms Step 3 Step 4
–
–
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