Actron AutoTroubleShooter CP7677 User Manual 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 voltage

or resistance based on the amount of

oxygen in the exhaust stream. A low

voltage (high resistance) indicates a lean

exhaust (too much oxygen), while a high

voltage (low resistance) indicates a rich

exhaust (not enough oxygen). The com-

puter uses this voltage to adjust the air/

fuel ratio. The two types of O

Sensors

commonly in use are Zirconia and Tita-

nia. Refer to illustration for appearance

differences of the two sensor types.

Test Procedure (see Fig. 31):

1. If engine is HOT, let it COOL down

before proceeding.

2. Remove Oxygen Sensor from ve-

hicle.

3. Insert BLACK test lead into COM

test lead jack.

4. Insert RED test lead into

test lead jack.

Titania-Type

Oxygen Sensor

Zirconia-Type

Oxygen Sensor

Exposed

flat element

Flutes

Rich Lean

Red

5. Test heater circuit.

• If sensor contains 3 or more wires,

then your vehicle uses a heated O

sensor.

• Refer to vehicle service manual for

location of heater pins.

• Connect RED test lead to either

heater pin.

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

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

harness

Ground

Black

Fig. 31

Oxygen (O

) Type Sensors

1 2 ... 22 23 24 25 26 27 28 29 30 31 32 33 34

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Actron AutoTroubleShooter CP7677 User Manual Page 27

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