Mercury MerCruiser MCM 454 Mag MPI Service Manual page 651

GENERAL SYSTEM DIAGNOSTICS
Chart A-1 (2 of 4): No Malfunction Indicator Lamp (MIL) - (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:
Inspect the ECM harness and connectors for improper mating, broken locks, improperly
formed or damaged terminals, poor terminal to wire connection, and damaged harness.
If the engine runs OK, check for a faulty light bulb or an open in the MIL driver circuit (CKT
419). If the engine cranks but will not run, check for an open ECM ignition or battery feed
or a poor ECM to engine ground.
TEST DESCRIPTION:
Number(s) below refer to the step number(s) on the Diagnostic Table:
3. This step ensures that battery voltage is available to terminal "F" of the DLC connector.
4 . This step checks for ground present at terminal "E" of the DLC connector. This indicates
the ECM is capable of completing the ground to the MIL.
5 . This step isolates the cause of an incomplete ground circuit to either faulty wiring or
faulty ECM circuitry.
7 . This step ensures that battery voltage is available to the ECM.
Index
Page 5E-58
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SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999