Mercury MerCruiser MCM 454 Mag MPI Service Manual page 656

SERVICE MANUAL NUMBER 23
Chart A-2 (2 of 3): Malfunction Indicator Lamp "On" Steady - No DLC Data or
Will Not Flash DTC 12 - Marine Diagnostic Trouble Code (MDTC) Tool Installed
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.
TEST DESCRIPTION:
Number(s) below refer to the Step number(s) on the Diagnostic Table.
3. If the light goes "OFF" when the ECM connectors are disconnected, CKT 419 is not
4. This step will check for an open diagnostic CKT 451.
6. If there is a problem with the ECM that prevents a scan tool from reading serial data, the
9. At this point, the MIL wiring is OK. If DTC 12 does not flash, replace the ECM.
NOTE: Before replacing ECM, check the MDTC tool on another engine to make sure it is
working properly.
Index
90-861326--1 MARCH 1999
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Poor connection or damaged harness. Inspect the ECM harness and connectors for
improper mating, broken locks, improperly formed or damaged terminals, poor terminal
to wire connection, and damaged harness.
shorted to ground.
ECM will not flash a DTC 12. If DTC 12 is flashing, check for short to ground in CKT 451
and verify that the scan tool is working properly on another engine.
GENERAL SYSTEM DIAGNOSTICS
Page 5E-63