Mercury MerCruiser MCM 454 Mag MPI Service Manual page 774

SERVICE MANUAL NUMBER 23
Code 42 (2 of 3): Ignition Control (IC) Circuit (Non-Scan) - Grounded IC Circuit,
Open Bypass Circuit, or Grounded Bypass Circuit
DIAGNOSTIC AIDS:
Check for the following conditions;
TEST DESCRIPTION:
Index
90-861326--1 MARCH 1999
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Poor connections at ECM. Inspect harness connectors for backed out terminals,
improper mating, broken locks, improperly formed or damaged terminals, and poor
terminal to wire connections.
Damaged harness. Inspect the wiring harness for damage.
If the engine starts and stalls, it may set a false trouble code 42. Clear trouble codes and
repair stalling condition.
Step 2. Trouble code 42 means the ECM has seen a grounded IC circuit, an open by-
pass circuit, or a grounded bypass circuit. This test confirms trouble code 42 and that
the fault causing the trouble code is present.
Step 3. Check for a normal IC ground path through the IC module. An IC CKT 423
shorted to ground will also read than 3000 Ohms.
Step 4. When the test light touches CKT 424, the module should switch, causing the
DVOM reading to go from over 3000 Ohms to under 1000 Ohms. The importance is that
the module switched.
Step 5. The module did not switch and this step checks for Bypass CKT 424 open, By-
pass CKT 424 shorted to ground, or faulty ignition module.
Step 7. Confirms that trouble code 42 is a faulty ECM and not an intermittent in CKT 423
or CKT 424.
STEP
Was the "On-Board Diagnostic" (OBD) System
1
Check Performed?
2 1. Install Marine Diagnostic Code Tool.
2. Clear trouble code 42.
3. Start engine and idle for 2 minutes or Ma-
rine Diagnostic Code Tool indicates a stored
trouble code.
4. Ignition "ON," engine "OFF."
7. Switch Marine Diagnostic Code Tool to
"Service Mode" and note trouble code.
Is trouble code 42 present?
ACTION
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
VALUE YES
PROCEED TO
– Step 2
– Step 3
Page 5G-29
NO
Go to
OBD
System
Check
Step 13