Hello:

I have a 1991 Pontiac Grand Am with a 2.5 liter 4 cylinder engine in my
shop with a radiator fan control problem.  If the air conditioning
compressor is running, the radiator fan runs. If the air conditoner is
switched off, the radiator fan turns off.  The radiator fan does not
run, no matter how hot the coolant gets.  I have already replaced the
temperature sensor, located just below the thermostat housing with a
Borg Warner WT 3081.  When cold, the resitance across the sensor is
almost 2000 ohms. When hot, the resistance across it is about 150 ohms.
The sensor connects to inputs on the ECM module with a black and a
yellow wire.  If I start the engine with the sensor unplugged from the
ECM module, the check engine light comes on. If I start the engine with
the sensor plugged into the ECM module, the check engine light does NOT
come on. The temperature gauge in the dash gives correct readings at
all times. What could be wrong? Also, I have thought about installing a
toggle switch to send power to the fan control relay to turn the fan on
when the Air Conditioning is off, but I can't locate the fan control
relay.  Where is it? I have a full wiring diagram of the car in a Hanes

manual, but still haven't been able to track down the problem.  I can
send a scan of the wiring schematics to anyone who might need to see
them to help me.
Robert McPherson 502) 367-9324 or (502) 298-6997