MerCruiser 305 CID (5.0L) Service Manual page 703

DIAGNOSTICS
Code 42 (1 of 3): Ignition Control (IC) Circuit
DISTRIBUTOR
IGNITION
COIL
When the system is running on the ignition module or in crank mode, there is no voltage on
CKT 424 and the ignition module grounds CKT 423. The ECM expects to detect a low volt-
age on CKT 423 during this condition. If the ECM sees voltage, it sets Code 41 and will not
go into the Ignition Control (IC) mode.
When the rpm for IC is reached (about 300 rpm), and CKT 424 voltage applied, CKT 423
should no longer be grounded in the ignition module, and the voltage should be varying.
If CKT 424 is open or grounded, the ignition module will not switch to IC mode. The CKT
423 voltage will be low and Code 42 will be set.
If CKT 423 stays grounded, the IC module will switch to IC mode but, because the line is
grounded, there will not be an IC signal and a trouble code 42 will be set.
DIAGNOSTIC AIDS:
Check for the following conditions:
•
Poor connection at ECM. Inspect harness connectors for backed out terminals,
improper mating, broken locks, improperly formed or damaged terminals, and poor
terminal to wire connection.
•
Damaged harness. Inspect the wiring harness for damage.
•
If the engine starts and stalls, it may set a false DTC 41 or 42. Clear DTC and repair
stalling condition.
After repairs, clear DTC following "Clearing Trouble Codes" procedure at the front of this
section. Failure to do so may result in DTC not properly being cleared.
Index
Page 5G-76
IC MODULE
A B
902 RED
3 PNK
121 BRN OR GRY
121 WHT TACH
SERVICE MANUAL NUMBER 24
ECM
MEFI 1 MEFI 3
MEFI 2
J2-23 J1-10
J2-8 J2-10
J2-24 J1-24
J2-6 J1-3
90-861327--1 OCTOBER 1999