103
Engine Coolant
Temperature (ECT)
Switch/Thermistor
The ECT switch/thermistor is a two-function device. One
side is a normally open, temperature activated switch that
closes when high coolant temperature is detected activat-
ing the high temperature circuit in the speedometer/LCD.
The other side contains a temperature sensitive resistor
(thermistor) that provides temperature information to the
glow plug controller/relay. To test the ECT switch/therm-
istor, use the following procedure.
1. Suspend the ECT switch/thermistor and a thermome-
ter in a container of cooking oil.
NOTE: Neither the ECT switch/thermistor nor the
thermometer should be allowed to touch the bottom
of the container or inaccurate readings will occur.
Use wire holders to suspend the ECT switch/thermis-
tor and thermometer.
2. Connect one meter lead to the base of the switch/
thermistor and the other meter lead to the switch pin.
With the meter in the OHMS position, the meter
should read an open circuit.
DE650A
3. Remove the meter lead from the switch pin and con-
nect to the thermistor pin; then heat the oil and note
the temperature and meter readings.
4. When the temperature reaches 20° C (68° F), the
meter should read 1k ohms.
5. When the temperature reaches 40° C (104° F), the
meter should read 460 ohms.
6. When the temperature reaches 50° C (122° F), the
meter should read 320 ohms.
7. Remove the meter lead from the thermistor pin and
connect to the switch pin; then continue to heat the
oil.
8. When the temperature reaches approximately 110° C
(230° F), the meter should read less than 1 ohm.
Glow Plug Controller/
Relay
The glow plug controller/relay is a plug-in device located
under the seat. The glow plug controller/relay applies 12
DC volts to the glow plugs in the pre-combustion cham-
bers to aid in cold starting. Heating time is determined by
the ECT thermistor signal and will vary from 0 seconds
(warm engine) to approximately 30 seconds (cold
engine).
NOTE: The glow plug controller/relay is not a ser-
viceable component. To test the controller/relay, use
the following procedure.
1. Using an appropriate multimeter, select DC Volts and
connect the black (-) tester lead to the black (85) wire
and the red (+) tester lead to the red/orange (30)
wire. The meter must read battery voltage. If no bat-
tery voltage is present, check the connection at the
starter relay.
2. Connect the red tester lead to the white/blue (87)
wire and momentarily turn the ignition switch to the
ON position. The meter should read battery voltage
for up to 30 seconds; then drop to zero.
3. Connect the red tester lead to the yellow/orange (L) wire
and turn the ignition switch to the ON position. The
meter should read battery voltage and the green glow
plug indicator should illuminate for up to 30 seconds.
4. Turn the ignition switch off.
5. Turn the ignition switch to the ON position. Observe
the glow plug indicator while momentarily “bump-
ing” the starter button. The glow plug indicator
should immediately extinguish.
6. If steps 2, 3, or 5 are not as specified, replace the
glow plug controller/relay.
7. If the glow plugs remain on for more than 35 sec-
onds, test the ECT switch/thermistor (thermistor side
only).
NOTE: To test the glow plugs, use the following pro-
cedure.
1. Disconnect the white/blue glow plug power wire
from the right-side glow plug; then disconnect the
jumper wire running to the left-side glow plug.
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! WARNING
Wear insulated gloves and safety glasses. Heated oil
can cause severe burns.
Manual
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