I have a 1999 cavalier and my coolant fan runs even when the engin is cold this problem is intermitent could it be my coolant sensor

CHECK COOLANT LEVEL MOST NEWER VECHICLE DONT HAVE RADIATOR CAP YOU HAVE TO POUR COOLANT IN THE COOLANT OVERFLOW JUG THE COOLANT WILL GO TO RADIATOR. IF THE COOLANT OVERFLOW JUG EMPTY ADD COOLANT UNTIL COOLANT LEVEL STOP DROPPING AT STAY AT FULL COLD MARK.IF COOLANT OKAY,NEED TO REPLACE THERMOSTAT AND COOLANT OVERFLOW JUG PRESSURE CAP. IF ALL BEEN DONE. MOST OF THE TIME WHEN CAR OVERHEATING WHILE MOVING. RADIATOR CORES STOPPED UP OR RADIATOR GRILLE DIRTY OR RESRICTED.ENGINE BLOCK COOLANT PASSAGES CLOGGED AND HEATER CORE CLOGGED.CHECK WATER PUMP SEE IF WATER PUMP WEEP HOLE LEAKING IF SO REPLACE WATER PUMP.IF ENGINE OVERHEATING AT A LONG TRAFFIC LINE ENGINE COOLING FANS NOT RUNNING EITHER COOLING FANS FUSE AND RELAYS BAD.OR ENGINE COOLANT TEMPERATURE BAD. THE ENGINE COOLANT TEMPERATURE SENSOR TURNS ON COOLING FANS AT A CERTAIN TEMPERATURE IF SENSOR BAD FANS WONT TURN ON. MAKE SURE YOU HAVE 50 /50 MIXTURE OF COOLANT AND WATER IN COOLING SYSTEM.

OVERHEATING CAN BE CAUSE BY MANY THINGS LIKE FAULTY THERMOSTAT AND FAULTY RADIATOR PRESSURE CAP,TOO MUCH WATER IN COOLANT SYSTEM NEED 50 / 50 WATER AND ANTIFREEZE.LOOK FOR WATER PUMP WEEP HOLE LEAK, IF COOLANT LEAKING OUT WEEP HOLE WATER PUMP BAD NEED REPLACING.CHECK FOR LOW COOLANT LEVEL, YOUR RADIATOR OVERFLOW JUG SHOULD HAVE COOLANT AT THE FULL COLD MARK IF NOT KEEP ADDING COOLANT INTO COOLANT OVERFLOW JUG UNTIL COOLANT STOP DROPPING AND FULL COLD MARK, IF OVERFLOW COOLANT JUG WAS EMPTY RADIATOR IS LOW ON COOLANT.WHICH CAUSE AIR IN COOLANT SYSTEM KEEPING THE ENGINE COOLANT TEMPERATURE SENSOR FROM BEING SUBMERGE IN HOT COOLANT WHICH TURN ON THE COOLANT FANS.WHEN ENGINE COOLANT TEMPERATURE GET CERTAIN SET TEMPERATURE LIKE 190 DEGREES THE PCM AND COOLANT SENSOR WILL TURN ON COOLANT FANS, IF VECHICLE OVERHEATING COOLANT FANS NOT WORKING EITHER YOU HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR CHECK COOLANT FANS FUSE AND RELAYS. YOU CAN CODE SCAN CAR TO SEE IF YOU HAVE FAULTY PCM, FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR FAULTY COOLANT FAN RELAY.IF COOLANT FAN AND ENGINE COOLANT TEMPERATURE SENSOR OKAY,YOU HAVE CORRECT COOLANT LEVEL IN COOLANT SYSTEM, THERMOSTAT AND RADIATOR PRESSURE CAP BEEN REPLACED, YOU COULD HAVE BLOWN HEAD GASKET CHECK ENGINE OIL LOOKS LIKE MILK SHAKE HEAD GASKET BLOWED ALSO WHEN HEAD GASKET BLOWED YOU CAN DRIVE CAR SHORT DISTANCE START OVERHEATING AND YOU LOOSE ENGINE POWER SUSPECT BLOWED HEAD GASKET.

REPLACE THERMOSTAT BUT IT SOUND LIKE FAULTY COOLANT TEMPERATURE SENSOR.BUT CHECK COOLING FAN FUSE AND RELAY.IF ALL IS GOOD HOT WIRE COOLING FAN IF COOLING FAN WORKS.PROBLEM COULD BE FAULTY COOLANT TEMPERATURE SENSOR. DAMAGE FAN WIRING OR FAULTY PCM.IF COOLING FAN DONT RUN WHEN HOT WIRED.REPLACE FAN AND MOTOR.

It's located on the left top front of the motor. It's threaded into the coolant tube.
If you're having trouble with your electric radiatior fan, if you disconnect the wire plug from it and if the fan is OK, it will start running after 5 seconds or so, if the fan doesn't start it's more than likley the temp. switch.

The electric fan should run all the time when the air conditioning is on.

CHECK COOLING FAN FUSE AND RELAY.IF BOTH GOOD SCAN CAR TO CHECK COOLANT TEMPERATURE SENSOR FAULT CODE.THE PCM AND COOLANT TEMP. SENSOR IS WHAT CAUSE FAN TO RUN AT CERTAIN TEMPERATURE.IF ALL IS GOOD.HOT WIRE COOLING FAN USING JUMPER WIRES TO BATTERY.IF FAN DONT RUN REPLACE FAN MOTOR.IF FAN RUNS YOU HAVE SHORT OR BROKE WIRE IN THE COOLING FAN ELECTRICAL CONNECTOR.

A BAD COOLANT TEMPERATURE SENSOR CAN CAUSE MISFIRE AND COOLANT FAN TURN ON WITH A COLD ENGINE.

REPLACE THE THERMOSTAT

sound like coolant temperature sensor is open or not working.scan it to see when engine get operating temperature when coolant temperature get 190 degrees the coolant temp sensor should show 190 degrees if it shows 80 degrees or lower it not working replace it.the coolant sensor control coolant fan.when it gets hot it resistance changes or lower.the pcm grounds it .then cooling fans will run.

since you have already tested fan and relay and both work, the problem may be the engine temp sensor. There are two sensors. One goes to instument cluster. This is engine coolant temp sensor, the other is engine temp sensor which is usually attached to engine block, sometimes they are connected to thermostat housing with the coolant sensor. You can pully the engine temp sensor and test that sensor same way as relay. (with mulitimeter)

check the coolant for hydrocarbons as that will comfirm the headgasket problem all those symptoms would indicate..