Actron AutoTroubleShooter CP7677 User Manual download pdf (Page 29)

29

1. If engine is HOT let it COOL down

before proceeding.

Make sure all engine and transmis-

sion fluids are at outside air tem-

perature before proceeding with this

test!

2. Insert BLACK test lead into COM

test lead jack.

3. Insert RED test lead into

test lead jack.

4. Disconnect wiring harness from

sensor.

5. If testing Intake Air Temperature

Sensor - Remove it from vehicle.

All other temperature sensors can

remain on vehicle for testing.

6. Connect RED test lead to either

sensor pin.

7. Connect BLACK test lead to re-

maining sensor pin.

8. Turn multimeter rotary switch to

desired OHM range.

If the approximate resistance is un-

known, start at the largest OHM

range and decrease to the appropri-

ate range as required. (See Setting

the Range on page 6)

Red

Black

Hair Dryer

Typical

Intake Air

Temperature

Sensor

9. View and record reading on dis-

play.

10.Disconnect multimeter test leads

from sensor and reconnect sen-

sor wiring.

This step does not apply to intake air

temperature sensors. For intake air

temperature sensors, leave multim-

eter test leads still connected to sen-

sor.

11.Heat up sensor.

If testing Intake Air Temperature Sen-

sor:

• To heat up sensor dip sensor tip

into boiling water, or...

• Heat tip with a

lighter if sensor tip is

metal or a hair dryer if sensor tip is

plastic.

• View and record smallest reading

on display as sensor is heated.

• You may need to decrease the

range to get a more accurate read-

ing.

For all other temperature sensors:

• Start engine and let idle until upper

radiator hose is warm.

• Turn ignition key OFF.

• Disconnect sensor wiring harness

and reconnect multimeter test

leads.

• View and record reading on dis-

play.

12.Test Results.

Good Sensor:

• Temperature sensors HOT resis-

tance is at least 300Ω less than its

COLD resistance.

• The key point is that the COLD re-

sistance decreases with increasing

temperature.

Bad Sensor:

• There is no change between the

temperature sensors HOT resis-

tance from the COLD resistance.

• The temperature sensor is an open

or a short circuit.

A temperature sensor is a thermistor or

a resistor whose resistance changes with

temperature. The hotter the sensor gets,

the lower the resistance becomes. Typi-

cal thermistor applications are engine

coolant sensors, intake air temperature

sensors, transmission fluid temperature

sensors, and oil temperature sensors.

Test Procedure (see Fig. 32):

Fig. 32

Temperature Type Sensors

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

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