Kohler COMMAND CH18-745 User Manual download pdf (Page 70)

5B.11

Section 5B

EFI Fuel System

Figure 5B-12. Cutaway of Oxygen Sensor.

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

Sensor

Safe.”

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.

“24 Pin” (MSE 1.0) Plastic-Cased ECU: Check

between the #6 and #4 pin terminals.

“32 Pin” (MSE 1.1) Plastic-Cased ECU: Check

between the #6 and #4 pin terminals.

5. Unplug the sensor connector and check sensor

resistance separately. Resistance value should

again be 2375-2625

ΩΩ

Ω.

a. If the resistance is out of specifications,

replace the temperature sensor.

b. If it is within specifications, proceed to Step 6.

6. Check the temperature sensor circuits (input,

ground) from the main harness connector to the

corresponding terminal in the sensor plug for

continuity, damage, etc.

“35 Pin” (MA 1.7) Metal-Cased ECU: Pin circuits

#14 and #27.

“24 Pin” (MSE 1.0) Plastic-Cased ECU: Pin

circuits #6 and #4.

“32 Pin” (MSE 1.1) Plastic-Cased ECU: Pin

circuits #6 and #4.

Oxygen Sensor

Figure 5B-11. Oxygen Sensor.

General

The oxygen sensor functions like a small battery,

generating a voltage signal to the ECU, based upon

the difference in oxygen content between the exhaust

gas and the ambient air.

The tip of the sensor, protruding into the exhaust gas,

is hollow (see cutaway Figure 5B-12). The outer

portion of the tip is surrounded by the exhaust gas,

with the inner portion exposed to the ambient air.

When the oxygen concentration on one side of the tip

is different than that of the other side, a voltage signal

typically cycling between 0.2 and 1.0 volt is generated

between the electrodes and sent to the ECU. The

voltage signal tells the ECU if the engine is straying

from the ideal 14.7:1 fuel mixture, and the ECU then

adjusts the injector pulse accordingly.

1. Connection Cable

2. Disc Spring

3. Ceramic Support Tube

4. Protective Sleeve

5. Contact Element

6. Sensor Housing

7. Active Ceramic Sensor

8. Protective Tube

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Kohler COMMAND CH18-745 User Manual Page 70

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