Mercury MerCruiser MCM 454 Mag MPI Service Manual page 729

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TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI

Code 42 (2 of 3): Ignition Control (IC) Circuit (Scan)

DIAGNOSTIC AIDS:

Refer to "Intermittents" in "Troubleshooting."

An intermittent problem may be caused by a poor or corroded connection, rubbed through

wire connection, a wire that is broken inside the insulation, or a corroded wire.

Any circuitry that is suspected as causing the intermittent complaint should be thoroughly

checked for backed-out terminals, improper mating, broken locks, improperly formed or

damaged terminals, poor terminal-to-wiring connections, corroded terminals and/or wiring,

or physical damage to the wiring harness. After repairs, clear codes following "Clearing

Codes" at the front of this section. Failure to do so may result in codes not properly being

TEST DESCRIPTION:

Number(s) below refer to step number(s) on the diagnostic table.

Step 2. Code 42 means the ECM has seen an open or short to ground in the IC or bypass

circuits. This test confirms Code 42 and that the fault causing the code is present.

Step 4. Check for a normal IC ground path through the ignition module. An IC CKT 423

shorted to ground will also read more than 3000 ohms; however, this will be checked later.

Step 7. As the test light voltage touches CKT 424, the module should switch, causing the

DVOM reading to go from over 3000 ohms to under 1000 ohms. The important thing is that

the module "switched."

Step 8. The module did not switch and this step checks for:

IC CKT 423 shorted to ground.

Bypass CKT 424 open.

Faulty ignition module connection or module.

Step 9. Confirms that Coded 42 is a faulty ECM and not an intermittent in CKT 423 or CKT

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Was the "On-Board Diagnostic" (OBD) System

Check Performed?

1. Clear codes.

2. Idle engine for one minute or until code 42

Does code 42 set?

Code 42 is intermittent, refer to "Diagnostic

SERVICE MANUAL NUMBER 23

90-861326--1 MARCH 1999

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