Here's the text from the service manual to help you figure out the problem
’HOT’ LIGHT OPERATION
With the ignition switch (and engine stop switch) “ON”,
power is delivered to the hot light via the Red/White
wire. The Blue/White wire (ground) out of the light
socket is connected to the PDM. If engine coolant
reaches the specified temperature, the thermistor
sends a signal to the PDM, which completes the
ground path for the light. An open thermistor will
cause the engine hot indicator to light and cause the
fan motor to come on.
HOT LIGHT CIRCUIT TEST
1. Disconnect the thermistor.
2. Turn key and auxiliary switch to “ON” position.
The hot lamp (and fan) should come on. Check
the bulb and related wiring if the lamp does not
illuminate. Check PDM for proper operation.
FAN BYPASS TEST
1. Disconnect the harness from the thermistor.
2. Turn ignition key (and engine stop switch) “ON”.
The fan (and hot indicator) should turn on.
3. If the fan does not run or runs slowly check the fan
motor wiring, ground, motor condition (refer to
FanMotor Testing this section) and PDM. Repair
or replace as necessary.
OIL COOLER FAN CONTROL TEST
Oil Cooler Fan Notes
GThermistor resistance decreases with
GBoth fan and hot indicator should be on
with the thermistor unplugged
GFan blade should rotate drawing air in
through cooler (blowing on engine)
Thermistor / Fan Control Test
GTurn key switch to ON and engine stop
switch to RUN. Do not start engine.
GTest voltage on R/W wire at vehicle control
module. R/W wire should have 12--14
Volts DC (battery voltage)
GDisconnect thermistor leads from the main
harness (Black/Yellow wires) - Fan and
Hot indicator ON? (If not, test
speedometer, fan motor and circuit)
GTest the resistance of the thermistor (refer
to temperature/resistance table).
Replace thermistor if out of specified range.
See the wiring diagram or chart for
thermistor resistance values at various oil
temperatures. The resistance of the
thermistor is approximately100kΩ at 77°F.
GReplace vehicle control module and test
system if all else appears okay.
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