Mercury MerCruiser MCM 454 Mag MPI Service Manual page 771

TROUBLE CODE DIAGNOSTICS - 7.4L MPI
DIAGNOSTIC AIDS:
Check for the following conditions;
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 41. Clear trouble codes and
repair stalling condition.
TEST DESCRIPTION:
Step 2. Trouble code 41 means the ECM has seen an open in the IC circuit. This test con-
firms trouble code 41 and that the fault causing the trouble code is present.
Step 3. Check for a normal IC ground path through the IC module.
Step 4. Confirms that trouble code 41 is a faulty ECM and not an intermittent open in CKT
423.
Code 41 (2 of 3): Ignition Control (IC) Circuit (Non-Scan) - Open IC Circuit
STEP
1
2
3
Index
Page 5G-26
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ACTION
Was the "On-Board Diagnostic" (OBD) System
Check Performed?
1.Install Marine Diagnostic Code Tool.
2. Clear trouble code 41.
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 41 present?
1. Ignition "OFF."
2. Disconnect ECM harness connectors.
3. Using a DVOM set on OHMS, probe
ECM harness terminal J2-23 to ground.
Is resistance within specified value?
SERVICE MANUAL NUMBER 23
VALUE YES NO
PROCEED TO
Go to
OBD
– Step 2
System
Check
– Step 3 Step 8
3000 to
6000
Ohms
Step 4 Step 5
90-861326--1 MARCH 1999