Kohler Aegis LH775 Service Manual page 43

Flow Chart Diagnostic Aids
Diagnostic Aid #1 SYSTEM POWER (MIL does not
illuminate when key is turned ON)
Possible causes:
● Battery
● Main system fuse
● MIL light bulb burned out
● MIL electrical circuit problem. Pin circuits 29 and 84.
● Ignition switch
● Permanent ECU power circuit problem. Pin circuit 1.
● Switched ECU power circuit problem. Pin circuit 2.
● ECU grounds
● ECU
Diagnostic Aid #2 FAULT CODES (Refer to detailed fault
code listing before fl ow chart and servicing information
for respective components)
● Code 21 - Engine Speed Synchronization
● Code 22 - Throttle Position Sensor (TPS)
● Code 23 - Engine Control Unit (ECU)
● Code 31 - Oxygen Sensor
● Code 32 - Oxygen Sensor
● Code 33 - Fuel System (temporary adaptation factor)
● Code 34 - Fuel System (permanent adaptation factor)
● Code 42 - Engine (Coolant) Temperature Sensor
● Code 43 - TPS Auto-Learn Initialization Function.
(Below Min. Limit)
● Code 44 - TPS Auto-Learn Initialization Function.
(Above Max. Limit)
● Code 51 - Injector 1
● Code 52 - Injector 2
● Code 55 - MIL (Diagnostic Light)
● Code 56 - Pump Relay
● Code 61 - End of Fault/Blink Code Transmission.
Diagnostic Aid #3 RUN/ON (MIL remains ON while
engine is running)
Possible causes:
● Fault codes which turn on MIL when engine is running.
● Code 21 - Engine Speed Synchronization
● Code 22 - Throttle Position Sensor (TPS)
● Code 23 - Engine Control Unit (ECU)
● Code 31 - Oxygen Sensor (shorted)
● Code 34 - Fuel System (permanent adaptation at
limit)
● Code 42 - Engine (Coolant) Temperature Sensor
● Code 43 - TPS Auto-Learn Initialization Function
(Below Min. Limit)
● Code 44 - TPS Auto-Learn Initialization Function
(Above Max. Limit)
● Code 51 - Injector 1
● Code 52 - Injector 2
● Code 55 - MIL (Diagnostic Light)
● Code 56 - Pump Relay
● MIL circuit grounded between light and ECU. Pin
circuit 29.
● ECU
NOTE: MIL (diagnostic light) used must be a 1/4 watt
incandescent lamp. An LED style light will stay
on continuously (dim) and should not be used.
66 690 07 Rev. --
Diagnostic Aid #4 SPEED SENSOR (MIL does not turn
off during cranking) Indicates ECU is not receiving a
signal from speed sensor.
Possible causes:
● Speed sensor
● Speed sensor circuit problem. Pin circuits 9 and 10.
● Speed sensor/toothed wheel air gap
● Toothed wheel
● Flywheel key sheared
● ECU
Diagnostic Aid #5 FUEL PUMP (fuel pump not turning
on)
Possible causes:
● Fuel pump fuse
● Fuel pump circuit problem. Circuits 30, 87, and relay.
● Fuel pump
Diagnostic Aid #6 RELAY (relay not operating)
Possible causes:
● Safety switches/circuit(s) problem. Circuit 25.
● Relay circuit(s) problem. Circuits 28, 85, 30, and 87.
● Relay
● ECU grounds
● ECU
Diagnostic Aid #7 IGNITION SYSTEM (no spark)
Possible causes:
● Spark plug
● Plug wire
● Coil
● Coil circuit(s). Circuits 30, 31, 65, 66, relay and relay
circuit 30.
● ECU grounds
● ECU
Diagnostic Aid #8 FUEL SYSTEM-ELECTRICAL (no fuel
delivery)
Possible causes:
● No fuel
● Air in fuel rail
● Fuel valve shut off
● Fuel fi lter/line plugged
● Injector circuit(s). Circuits 14, 15, 45 and 4A.
● Injector
● ECU grounds
● ECU
Diagnostic Aid #9 FUEL SYSTEM (fuel pressure)
Possible causes for low fuel system pressure:
● Low fuel
● Fuel fi lter plugged
● Fuel supply line plugged
● Pressure regulator
● Fuel pump
Possible causes for high fuel system pressure:
● Pressure regulator
● Fuel return line plugged or restricted.
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