Kohler Aegis LH775 Service Manual page 37

DIAGNOSTIC CODE SUMMARY
Code 21
Component: Engine Speed Sensor
Fault: ECU receiving inconsistent tooth count
signals from speed sensor.
Condition: Possible misfi re as ECU attempts to
resynchronize, during which time fuel and
spark calculations are not made.
Conclusion: Engine Speed Sensor Related
● Sensor connector or wiring.
● Sensor loose or incorrect air gap.
● Flywheel key sheared
Speed Sensor Ring Gear Related
● Damaged teeth.
● Varying gap (gear loose/out of
alignment).
Engine Wiring Harness Related
● Pin circuits 9 and/or 10 wiring or
connectors.
● Shielding for pin circuits 9 and/or 10
damaged or not properly grounded.
● Poor or improper grounds in system
(battery, ECU, oxygen sensor,
shielding, fuel pump, ignition output).
● Pin circuits 9 and/or 10 routed near
noisy electrical signals (coils, spark
plug lead, plug connector).
ECU/Harness Related
● ECU-to-harness connection problem.
Ignition System Related
● Non-resistor spark plug(s) used.
66 690 07 Rev. --
Code 22
Component: Throttle Position Sensor (TPS)
Fault:
Condition:
Conclusion: TPS Sensor Related
Code 23
Component: ECU
Fault:
Condition:
Conclusion: ECU (internal memory problem).
KohlerEngines.com
Unrecognizable signal is being sent from
sensor (too high, too low, inconsistent).
A limp-home operating mode occurs,
with an overall decrease in operating
performance and effi ciency. Fuel delivery
is based upon oxygen sensor and fi ve
mapped values only. Rich running
(black smoke) will occur until closed
loop operation is initiated. A stumble or
misfi re on hard acceleration and/or erratic
operation may be exhibited.
● Sensor connector or wiring.
● Sensor output affected or disrupted by
dirt, grease, oil, wear, or breather tube
position (must be to side opposite
TPS).
● Sensor loose on throttle body manifold.
Throttle Body Related
● Throttle shaft or bearings worn/
damaged.
Engine Wiring Harness Related
● Pin circuits 4, 8, and/or 18 damaged
(wiring, connectors).
● Pin circuits 4, 8, and/or 18 routed near
noisy electrical signal (coils, alternator).
● Intermittent 5 volt source from ECU
(pin circuit 18).
ECU/Harness Related
● ECU-to-harness connection problem.
ECU is unable to recognize or process
signals from its memory.
Engine will not run.
● Diagnosable only through elimination
of all other system/component faults.
EFI System
37