Mercury MerCruiser MCM 454 Mag MPI Service Manual page 714

SERVICE MANUAL NUMBER 23
Code 43 (1 of 3): Knock Sensor (Ks) Circuit (Non-Scan)
CIRCUIT DESCRIPTION:
The ability to sense engine knock or detonation 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 retard timing.
DIAGNOSTIC AIDS:
If CKT 496 is routed too close to secondary ignition wires, the KS module may see the inter-
ference as a knock signal, resulting in false retard.
An intermittent problem may be caused by a poor or corroded connection, rubbed through
wire connection, a wire that is broken inside the insulation, or a corroded wire.
Any circuitry that is suspected as causing the intermittent complaint should be thoroughly
checked for backed-out terminals, improper mating, broken locks, improperly formed or
damaged terminals, poor terminal-to-wiring connections, corroded terminals and/or wiring,
or physical damage to the wiring harness. After repairs, clear codes following "Clearing
Codes" procedure at the front of this section. Failure to do so may result in codes not
properly being cleared.
TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic table.
Step 2. This step ensures that 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 checks if a voltage signal from the KS module is present at the ECM.
Index
90-861326--1 MARCH 1999
Downloaded from https://needmanual.com/
a
a - Knock Sensor Module
b - To System Relay
c - Starboard Knock Sensor
d - Port Knock Sensor
e - Knock Sensor Signal
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
FUSE 15A
b
485 GRN
PUR
c
e
d
Page 5F-17