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

TROUBLE CODE DIAGNOSTICS - 7.4L MPI
Code 41 (2 of 3): Ignition Control (IC) Circuit (Scan) Open IC Circuit
STEP
5
6
7
8
Code 42 (1 of 3): Ignition Control (IC) Circuit (Scan) - Grounded IC Circuit,
Open Bypass Circuit, or Grounded Bypass Circuit
CIRCUIT DESCRIPTION:
When the system is running on the ignition module or crank mode, no voltage on the bypass
line, the ignition module grounds the IC signal. The ECM expects to detect a low voltage on
the IC line during this condition. If the ECM sees 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, the IC
should no longer be grounded in the ignition module, so the IC voltage should be varying.
If the bypass line is open or grounded, the ignition module will not switch to IC mode. The
IC line, CKT 423 voltage will be low and 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.
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 ter-
minal 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's and repair
stalling condition.
After repairs, clear DTC's following "Clearing Trouble Codes" procedure at the front of this
section. Failure to do so may result in DTC's not properly being cleared.
Index
Page 5G-60
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ACTION
Locate and repair open in CKT 423. If a prob-
lem is found, repair as necessary. Was a prob-
lem found?
Replace faulty distributor ignition module. Is
action complete?
Repair faulty ECM connections or replace
faulty ECM. Is action complete?
Trouble code is intermittent. Refer to "Diagnos-
tic Aids" on facing page. Check harness and
connectors for an intermittent open in CKT
423.
SERVICE MANUAL NUMBER 23
VALUE YES NO
PROCEED TO
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Verify Verify
Repair
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90-861326--1 MARCH 1999
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