Cooling fan wont turn on

A pontiac montana ? There are three relay's that control your cooling fans ! unplug what sensor ? The engine coolant temp. sensor is an input to the PCM - engine computer . When temp. reaches 213 degrees the PCM energizes the relays , depending on low or high speed . Using a scan tool to see if the PCM will turn on the fans an checking engine coolant temp.data is the right way to diagnose this . Relay Driven Dual Cooling Fan Diagnostics

Smart man using a scanner for the actual temp. Assuming you're not losing coolant....2 things I'd look at here, 1st is you may have air in the system, make sure to purge all the air. 2nd is your fan clutch, I've replaced a few fan clutches in my own Trailblazer. Have had them bad right out of the box brand new. Have had bad brand new fan clutches on 2 of my last Trailblazers. You should hear it engaging especially in stop and go traffic.

Does the engine cool down when the fans are on?

the sending unit will not affect heat but if its broken it will effect the fuel control by giving computer false info, i dont think theres a problem with the temp unit, i think the thermostant is bad and is stuck open or you are very low on coolant, if the thermostat was stuck open then you would get some heat not very hot and would take a long time to get heat. i would start by replacing the thermostat, it is very important to bleed air from system after coolant change or thermostat replacing, after filling run engine until fan turns on , let cool some to release preasure then remove cap start engine and top off, drive for 15min then park let cool and recheck coolant, hope this helps,

will it sounds like u tryed everything except what could be cousing the problem it is probley the heater core is pluged with hard water or calcium build up or is just pluged and a rad flush wont flush the heater core unless you start the vechial and flushing the rad to do the heaterd core to turn on the heat to high and the fasters fan speed and make shore the van is running.

try the temp sending unit on the engine head.next to thermostat.

yes thermostats wear out. make sure your cooling fans are not running at the low temp you have. you may have a bad temp sending unit. also you gauge send ing unit could be bad.

eng.temp.coolant sensor,located on thermostat housing,if u think sensor is defect,this check will make engine light come on,unplug elect. connection on sensor while car is idling,cooling fan will start up within 1 min.if it doesnt check fans power circuit.or apply batt.voltage directly to fan to see if fan will work.

The water temp sensor is located near the thermostat housing. This sensor is what tells the ECM to turn the fan on/off. The water temp sending unit is located near the same area. You know you have the correct sensor is because the water temp sensor has a 2 prong plug. The water temp sending unit only has 1 prong.

sounds to me then that the temp. sending unit is giveing the pcm the wrong temp. unplug the temp sending unit and see what it does (usually located around the thermostat housing)