Kohler LH630-775 Service Manual page 70

Section 5B
EFI Fuel System
Code: 23
Source: ECU
Explanation: ECU is unable to recognize or process
signals from its memory.
Expected Engine
Response: Engine will not run.
Possible Causes:
1. ECU (internal memory problem).
a. Diagnosable only through the elimination of
all other system/component faults.
Code: 24 (will not blink out)
Source: Engine Speed Sensor
Explanation:
No tooth signal from speed sensor.
MIL light will not go out when
cranking.
Expected Engine
Response:
None-engine will not start or run as
ECU is unable to estimate speed.
Possible Causes:
1. Engine Speed Sensor Related
a. Sensor connector or wiring.
b. Sensor loose or air gap incorrect.
2. Speed Sensor Wheel Related
a. Damaged teeth.
b. Gap section not registering.
3. Engine Wire Harness Related
a. Pin circuit #9 and/or #10 wiring or
connectors.
4. ECU/Harness Related
a. ECU-to-harness connection problem.
Code: 31
Source:
Fuel Mixture or Oxygen Sensor
Explanation: "System to Lean" Oxygen sensor not
sending expected voltage to ECU.
Expected Engine
Response: System operates under "open loop"
control only. Until fault is detected
and registered by ECU, engine will
run rich if oxygen sensor is shorted to
ground or lean if it is shorted to
battery voltage. After fault is
detected, performance can vary,
depending on cause. If performance is
pretty good, the problem is probably
with the oxygen sensor, wiring, or
connectors. If the engine is still
running rich (laboring, short on
power) or lean (popping or misfiring),
5B.30
the fuel mixture is suspect, probably
incorrect TPS initialization or low
fuel pressure.
Possible Causes:
1. TPS Initialization Incorrect
a. Lean condition (check oxygen sensor signal
with VOA and see Oxygen Sensor section).
2. Engine Wire Harness Related
a. Pin circuit #20 wiring or connectors.
3. Oxygen Sensor Related
a. Sensor connector or wiring problem.
b. Exhaust leak.
c. Poor ground path to engine (sensor is case
grounded).
Code: 32
Source: Oxygen Sensor
Explanation: No change in the sensor output
signal.
Expected Engine
Response:
"Open loop" operation only, may
cause a drop in system performance
and fuel efficiency.
Possible Causes:
1. Engine Wiring Harness Related
a. Pin circuit #20 wiring or connectors.
2. Oxygen Sensor Related
a. Sensor connector or wiring problem.
b. Sensor contaminated or damaged.
c. Sensor below the minimum operating
temperature (375°C, 709°F).
d. Poor ground path to engine (sensor grounds
through shell, see Oxygen Sensor section).
Code: 33
Source: Oxygen Sensor/Fuel System
Explanation: "System to Rich" Temporary fuel
adaptation control is at the upper
limit.
Expected Engine
Response: Erratic performance. Will run rich
(smoke).
Possible Causes:
1. Fuel Supply Related (nothing lean – only rich)
a. Restricted return line causing excessive fuel
pressure.
b. Fuel inlet screen plugged (in-tank fuel pump
only).
c. Incorrect fuel pressure at fuel rail.