Mercury MerCruiser MCM 454 Mag MPI Service Manual page 810

SERVICE MANUAL NUMBER 23
Code 44 (1 of 3): Knock Sensor (KS) Circuit (Scan) - No Knock Detected
CIRCUIT DESCRIPTION:
Knock Sensor (KS) system circuit is accomplished with a module that sends a voltage signal
to the ECM. As the knock sensor detects engine knock, the voltage from the KS module to
the ECM drops, and this signals the ECM to start retarding timing. The ECM will retard timing
when knock is detected and RPM or engine coolant temperature is above a certain value.
DIAGNOSTIC AIDS:
Check for the following conditions:
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.
NOTE: if fuel octane is too high, a false DTC 44 may be set.
Index
90-861326--1 MARCH 1999
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a
a - Knock Sensor Module
b - To System Relay
c - Starboard Knock Sensor
d - Port Knock Sensor
e - Knock Sensor Signal
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.
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
FUSE 15A
b
485 GRN
PUR
c
e
d
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