Kohler COMMAND CH18, Service Manual

Page: 81 / 232

5B.12
Section 5B
EFI Fuel System
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 voltage reading between 0.2 v-1.0 v.
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 v-1.0 v,
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
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 (page 5B.13). 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 K
Ω Ω Ω Ω Ω
.
a. If the resistance is less than 2.0 K
Ω Ω Ω Ω Ω
, go to
Step 4.
b. If the resistance is greater than 2.0 K
Ω 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 sensor cool, the resistance
should be greater than
1.0 M
Ω Ω Ω Ω Ω
.
a. If the resistance is greater than 1.0 M
Ω Ω Ω Ω Ω
, go to
Step 5.
b. If the resistance is less than 1.0 M
Ω Ω Ω Ω Ω
, the
sensor is bad, replace it.
5. With the oxygen sensor disconnected and engine
not running, disconnect the main harness
connector from the ECU and set the meter to the
Rx1 scale. Check the circuit continuity as follows:
“35 Pin” (MA 1.7) Metal-Cased ECU: Check for
continuity from pin #9 of the ECU connector (see
page 5B.28) to the shell of the oxygen sensor, and
from pin #10 to the sensor connector terminal of
the main harness. Both tests should indicate
continuity.
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Check for
continuity from pin #15 of the ECU connector
(see page 5B.31) to the shell of the oxygen sensor,
and from pin #11 to the sensor connector terminal
of the main harness. Both tests should indicate
continuity.
“32 Pin” (MSE 1.1) Plastic Cased ECU: Check for
continuity from pin #19 of the ECU connector
(see page 5B.32) to the shell of the oxygen sensor,
and from pin #20 to the sensor terminal of the
main harness. Both tests should indicate
continuity.