Mercury MerCruiser MCM 454 Mag MPI Service Manual page 712

SERVICE MANUAL NUMBER 23
Code 42 (2 of 3): Ignition Control (IC) Circuit (Non-Scan)
DIAGNOSTIC AIDS:
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
cleared.
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 3. 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 6. As the test light voltage touches CKT 424, the module should switch, causing the
DVM reading to go from over 3000 ohms to under 1000 ohms. The important thing is that
the module "switched."
Step 7. The module did not switch and this step checks for:
Step 8. Confirms that Coded 42 is a faulty ECM and not an intermittent in CKT 423 or CKT
424.
Index
90-861326--1 MARCH 1999
Downloaded from https://needmanual.com/
IC CKT 423 shorted to ground.
Bypass CKT 424 open.
Faulty ignition module connection or module.
STEP
Was the "On-Board Diagnostic" (OBD) System
1
Check Performed?
1 Install Marine Diagnostic Code Tool.
2 Cl 2. Clear codes (refer to clearing codes). d
3 Idle engine for one minute or until mal- 3. Idle engine for one minute or until mal-
function indicator light comes ON.
2 2
4. Ignition ON, engine stopped.
5. Enter "Service Mode" on code tool and 5 E t "S
note codes. ote codes
Is Code 42 Present?
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
ACTION
( f t l i d
i M d " d t l
VALUE YES
PROCEED TO
– Step 2
)
– – Ste 3 Step 3
d
NO
Go to
OBD
System
Check
Ste 12 Step 12
Page 5F-15