Code 44 (1 Of 3): Knock Sensor (Ks) - Mercury MerCruiser MCM 454 Mag MPI Service Manual

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SERVICE MANUAL NUMBER 23

Code 44 (1 of 3): Knock Sensor (KS) Circuit (Non-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 "Clear DTC's Procedure" in the "General Information"

section. Failure to do so may result in DTC's not properly being cleared.

NOTE: lf fuel octane is too high, a false DTC 44 may be set.

TEST DESCRIPTION:

90-861326--1 MARCH 1999

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Knock Sensor Module

To System Relay

Starboard Knock Sensor

Port Knock Sensor

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.

Step 2. This step ensures the knock sensor circuitry is within the proper resistance

Step 3. Applying 12 volts with a test light to CKT 496 simulates a signal from the knock

sensor. The knock sensor is faulty if a response occurs.

Step 4. This step confirms the ability of the KS module to remove the voltage from the

signal line when it detects spark knock. Since the knock sensor produces an AC voltage

signal, it may be necessary to repeatedly touch (tickle) the harness connector with the

test light to simulate this type of signal.

TROUBLE CODE DIAGNOSTICS - 7.4L MPI

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