Actron CP7665 Operations Instructions download pdf (Page 27)

Testing Engine Sensors

In the early 1980’s, computer controls were installed in vehicles to meet

Federal Government regulations for lower emissions and better fuel economy.

To do its job, a computer-controlled engine uses electronic sensors to find

out what is happening in the engine. The job of the sensor is to take

something the computer needs to know, such as engine temperature, and

convert it to an electrical signal which the computer can understand. The

digital multimeter is a useful tool for checking sensor operation.

The Oxygen Sensor produces a volt-

age or resistance based on the

amount of oxygen in the exhaust

stream. A low voltage (high resis-

tance) indicates a lean exhaust (too

much oxygen), while a high voltage

(low resistance) indicates a rich ex-

haust (not enough oxygen). The

computer uses this voltage to ad-

just the air/fuel ratio. The two types

of O

Sensors commonly in use are

Zirconia and Titania. Refer to illus-

tration for appearance differences

of the two sensor types.

Test Procedure (see Fig. 27):

1. If engine is HOT, let it COOL

down before proceeding.

Titania-Type

Oxygen Sensor

Zirconia-Type

Oxygen Sensor

Exposed

flat element

Flutes

Rich Lean

Red

2. Remove Oxygen Sensor from

vehicle.

3. Insert BLACK test lead into

COM test lead jack.

4. Insert RED test lead into

test lead jack.

1-wire or 3-wire: Ground is sensor housing

2-wire or 4-wire: Ground is in sensor wiring

harness

Ground

Fig. 27

Oxygen (O

) Type Sensors

Black

1 2 ... 22 23 24 25 26 27 28 29 30 31 32

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Actron CP7665 Operations Instructions Page 27

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