Kohler LH630-775 Service Manual page 50

Section 5B
EFI Fuel System
The oxygen sensor can function only after being
heated by exhaust temperatures to a minimum of
375°C (709°F). A cold oxygen sensor will require
approximately 1-2 minutes at moderate engine load
to warm sufficiently to generate a voltage signal.
Proper grounding is also critical. The oxygen sensor
grounds through the metal shell, so a good, solid,
unbroken ground path back through the exhaust
system components, engine, and wiring harness is
required. Any disruption or break in the ground
circuit can affect the output signal and trigger
misleading fault codes. Keep that in mind when doing
any troubleshooting associated with the oxygen
sensor. The oxygen sensor can also be contaminated
by leaded fuel, certain RTV and/or other silicone
compounds, carburetor cleaners, etc. Use only those
products indicated as "O
Service
Like the other sensors already discussed, the oxygen
sensor is a non-serviceable component. Complete
replacement is required if it is faulty. The sensor and
wiring harness can be checked as follows.
NOTE: All tests should be conducted with a good
quality, high-impedance, digital VOA meter
for accurate results.
1. Oxygen sensor must be hot (minimum of 400°C,
725°F). Run engine for about 5 minutes. With the
engine running, disconnect the oxygen sensor
lead from the wiring harness. Set VOA meter for
DC volts and connect the red lead to the
disconnected sensor lead, and the black lead to
the sensor shell. Check for a cycling voltage
reading between 0.2 and 1.0 volt.
a. If voltage is in the specified range, go to step 2.
b. If the voltage is not in the specified range,
reconnect the oxygen sensor lead. With the
lead connected, probe or connect the sensor
connection with the red VOA meter lead.
Attach the black VOA meter lead to a known
good ground location. Start and run the
engine at 3/4 throttle and note the voltage
output.
The reading should cycle between 0.2 and 1.0
volt, which indicates the oxygen sensor is
functioning normally and also the fuel
delivery controlled by the ECU is within
prescribed parameters. If the voltage readings
show a steady decline, bump the governor
lever to make the engine accelerate very
5B.10
Sensor Safe."
2
quickly and check the reading again. If voltage
momentarily increases and then again
declines, without cycling, engine may be
running lean due to incorrect TPS
initialization. Shut off the engine, perform
TPS initialization, and then repeat the test. If
TPS initialization cannot be achieved,
perform step c.
c. Replace the oxygen sensor (see next page).
Run the engine long enough to bring the new
sensor up to temperature and repeat the
output test from step 1. The cycling voltage
from 0.2 to 1.0 volt should be indicated.
2. Move the black voltmeter lead to the engine
ground location and repeat the output test. The
same voltage (0.2 v-1.0 v) should be indicated.
a. If the same voltage reading exists, go on to
step 3.
b. If the voltage output is no longer correct, a
bad ground path exists between the sensor
and the engine ground. Touch the black lead
at various points, backtracking from the
engine ground back toward the sensor,
watching for a voltage change at each
location. If the correct voltage reading
reappears at some point, check for a problem
(rust, corrosion, loose joint or connection)
between that point and the previous
checkpoint. For example, if the reading is too
low at points on the crankcase, but correct
voltage is indicated when the black lead is
touched to the skin of the muffler, the flange
joints at the exhaust ports become suspect.
3. With sensor still hot (minimum of 400°C, 752°F),
switch meter to the Rx1K or Rx2K scale and
check the resistance between the sensor lead and
sensor case. It should be less than 2.0 KΩ Ω Ω Ω Ω .
a. If the resistance is less than 2.0 KΩ Ω Ω Ω Ω , go to
step 4.
b. If the resistance is greater than 2.0 KΩ Ω Ω Ω Ω , the
oxygen sensor is bad, replace it.
4. Allow the sensor to cool (less than 60°C, 140°F)
and retest the resistance with the meter set on
the Rx1M scale. With the sensor cool, the
resistance should be greater than 1.0 MΩ Ω Ω Ω Ω .