Isuzu C22NE Workshop Manual page 335

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 18)
DIGITALLY CONTROLED SIGNAL TO NOISE ENHANCEMENT FILTER FAILURE
Circuit Description
The knock sensor (KS) system is used to detect
engine detonation. The knock sensor produced an AC
voltage signal. The knock sensor sends this signal to
the ECM. The amplitude and the frequency of the AC
voltage signal depends upon the knock level being
detected. The ECM will then retard the spark timing
based on the signals from the Knock Sensor.
This code detects a digitally controlled signal to noise
enhancement filter failure. Then the DTC 18 will set.
Conditions for Setting the DTC
• ECM powered up, Engine running, Electronic spark
control enabled and Engine rpm is greater than 96
rpm.
• Malfunction 16 is not triggered.
Action Taken When the DTC Sets
• The Malfunction Indicator Lamp (MIL) will illuminate
the second time the fault is detected.
• The ECM will use a calculated spark retard value in
order to minimize the knock during the conditions
when the knock is likely to occur. The calculated
value will vary based on the engine speed and load.
DRIVEABILITY AND EMISSIONS 6E1-165
Conditions for Clearing the MIL/DTC
Once the ECM determines that a fault(s) has been
rectified then the CEL will switch OFF, although the
fault code will remain in the ECM memory.
Any fault codes will remain in ECM memory until -
1. They are cleared by disconnecting the Battery for
more than 30 seconds.
2. A service tool such as Tech 2 is used to clear them.
3. Ten consecutive starts without logging a fault.
Diagnostic Aids
Correct any abnormal engine noise before using the
diagnostic table.
Check for an open ignition feed circuit.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Table.
2. If the conditions for the test as described above are
met, a Diagnostic Trouble Code 18 will set and MIL
will illuminate.