30
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. I n s e r t R E D t e s t l e a d i n t o
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
display.
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
Sensor:
• 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 display.
12. Test Results.
Good Sensor:
• Temperature sensors HOT resis-
tance is at least 300
Ω
less than its
COLD resistance.
• The key point is that the COLD
resistance decreases with increas-
ing 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
600 600
