Open Bypass Circuit, Or Grounded; Bypass Circuit - Mercury MerCruiser MCM 454 Mag MPI Service Manual

TROUBLE CODE DIAGNOSTICS - 7.4L MPI
Code 42 (1 of 3): Ignition Control (IC) Circuit (Non-Scan) - Grounded IC Circuit,
Open Bypass Circuit, or Grounded Bypass Circuit
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CIRCUIT DESCRIPTION:
When the system is running on the ignition module or crank mode there is no voltage on the
bypass line, the ignition module grounds the IC signal. The ECM expects to detect no volt-
age on the IC line during this condition. If it detects a voltage, it sets Code 41 and will not
go into the IC mode.
When the RPM for IC is reached (about 300 RPM), and bypass voltage applied on CKT 424
by the ECM, the IC line should no longer be grounded in the ignition module. CKT 423 should
have varying voltage on it at this point.
If the bypass line is open or shorted to ground, the IC module will not switch to IC mode. The
IC line, CKT 423, voltage will be low and trouble code 42 will be set.
If CKT 423 is 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.
Index
Page 5G-28
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"C"
n
s
o
a
p
b
c
902 RED
t
o
3 PNK
q
r n
121 GRY
121 WHT
o
e
a - Ignition coil connector
b - Distributor
c - To system relay
d - Ignition coil
e - Distributor
f - In-line harness (Tach)
g - Ignition control module
h - Pick-up coil
i - Distributor 4 terminal connector
j - Ignition control (IC)
k - Dist. reference "high"
l - Bypass
Dist. reference "low"
n - Black Connector
o - Gray Connector
p - Tachometer
q - Secondary
r - Primary
s - Ignition
h
g
i
f
SERVICE MANUAL NUMBER 23
j
k
l
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90-861326--1 MARCH 1999