Kohler COMMAND CH18-745 User Manual download pdf (Page 71)

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

ΩΩ

Ω.

a. If the resistance is less than 2.0 K

ΩΩ

Ω, go to

Step 4.

b. If the resistance is greater than 2.0 K

ΩΩ

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

ΩΩ

Ω.

a. If the resistance is greater than 1.0 M

ΩΩ

Ω, go to

Step 5.

b. If the resistance is less than 1.0 M

ΩΩ

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.

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Kohler COMMAND CH18-745 User Manual Page 71

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