Actron AutoAnalyzer CP7665 - Manual (Page 27)

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
2
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
2
) Type Sensors
Black