SERVICE MANUAL NUMBER 23
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
Code 44 (1 of 3): Knock Sensor (KS) Circuit (Non-Scan) - No Knock Detected
FUSE 15A
b
a
e
485
GRN
PUR
c
d
a - Knock Sensor Module
b - To System Relay
c - Starboard Knock Sensor
d - Port Knock Sensor
e - Knock Sensor Signal
CIRCUIT DESCRIPTION:
Knock Sensor (KS) system circuit is accomplished with a module that sends a voltagesignal
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:
•
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.
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:
Step 2. This step ensures the knock sensor circuitry is within the proper resistance
value.
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.
90-861326--1
MARCH 1999
Page 5G-33
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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