Mercury MerCruiser MCM 454 Mag MPI Service Manual page 647

GENERAL SYSTEM DIAGNOSTICS
On-Board Diagnostic (OBD) System Check (Scan)
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m -
CIRCUIT DESCRIPTION:
The on-board diagnostic system check must be the starting point for any driveability com-
plaint diagnosis. Before using this procedure, you should perform a careful visual/physical
check of the ECM and engine grounds for being clean and tight.
The on-board diagnostic system check is an organized approach to identifying a problem
created by an electronic engine control system malfunction.
DIAGNOSTIC AIDS:
An intermittent may be caused by a poor connection, rubbed through wire insulation or a
wire broken inside the insulation. Check for the following items:
Inspect the ECM harness and connectors for improper mating, broken locks, improperly
formed or damaged terminals poor terminal to wire connection, and damaged harness.
Index
Page 5E-54
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a - ECM/DLC 15amp fuse
b - DLC Connector
c - Marine Diagnostic Code Tool
d - ECM, Injector Knock Sensor Module 10amp Fuse
e - (ORN-Some Models)
f - (BLK-Some Models)
g - Serial Data
h - ECM Ground
i - ECM Ground
j - Diagnostic Test Terminal
k - Malfunction Indicator Lamp (MIL)
l - Ignition Feed
Battery Feed
n - Battery Feed
e
461 ORN/BLK
f
451 WHT/BLK
d
SERVICE MANUAL NUMBER 23
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90-861326--1 MARCH 1999