Mercury MerCruiser MCM 454 Mag MPI Service Manual page 711

TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
Code 42 (1 of 3): Ignition Control (IC) Circuit (Non-Scan)
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CIRCUIT DESCRIPTION:
When the system is running on the ignition module, that is, no voltage on the bypass line,
the ignition module grounds the IC signal. The ECM expects to detect no voltage on the IC
line during this condition. If it detects a voltage, it sets Code 42 and will not go into the IC
mode.
When the rpm for IC is reached (about 300 rpm), and bypass voltage applied, the IC should
no longer be grounded in the ignition module, so the IC voltage should be fluctuating.
If the bypass line is open or grounded, the ignition module will not switch to IC mode so the
IC voltage will be low and Code 42 will be set.
If the IC line is grounded, the ignition module will switch to IC but, because the line is
grounded, there will be no IC signal. A Code 42 will be set.
Index
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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 - Distributor Reference "High"
l - Bypass
Distributor reference "Low"
n - Black Connector
o - Gray Connector
p - Tachometer
q - Secondary
r - Primary
s - Ignition
t - Ignition Coil
h
g
i
f
SERVICE MANUAL NUMBER 23
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90-861326--1 MARCH 1999