Shop Ford Coolant Temperature Sensors

i went back to the dealer and they told me what ever controls the iac is what is causing the truck to idle high. anyone know what controls the iac valve

We changed the gauge. It is a VDO 0-250 temp. it only got to 200 this time. also we put a chip in it. Do you think this would cause it to get hot ?

Thx for the reply Larry

200F would be in normal range if it starts getting going around the 250F then I would worry.


IF it gets hot again feel both upper and lower rad hoses. If one is hot and one is cold you have flow issue or air in the system. I would also get a chemical test done to make sure it's not a headgasket leak. No a chip won't cause it to overheat.

The flex fan is not the best cooling method .It flattens out in low speed high revs situations ,as in offroading , which gives you little airflow. IF class rules permit it get an electric unit mounted to radiator frame . You'll gain a few ponies to boot.

hmmmmm sounds like my 92 grand am. i got a spark and i got fule. i've even checked the timing everything is ok. the only thing i can think of is the computer. if the check engine light comes on i'd start with that.

Thats the only thing thst we can think of as well. The check engine light has never been on before. Do we have to take the car to the dealership to get the computer tested?

well sometimes yes. its a 99 so i do know it's got the obd2 computer system in it. you can get a tester at a parts shop. it hooks up to the diognostic hook up under the dash board. usually on the drivers side. it might be cheaper to do it your self but i'd ask the guy at the parts shop. you might have to take it to the dealer or a automotive place.

You need to just go back and check your work. Look for damage to the intake snorkel or hoses left disconnected that attach to it.

everything is plugged in, all vacuum lines are connected, air intake is all tight and connected.

What's the code number that it's currently setting?

"111" over and over. which means system okay.

during the testing of the maf sensor both my ground and hot are good, its when i get to letter "c" which is "signal ground" ground coming from the ecu, its suppose to be reading 12 volts as well and it isnt. is this a problem with the ecm or sometihng else?

ok so i disconnected neg - battery cable and reset the ecu, now it will run with the MAF plugged in but idles really really rough. i have to give it a little gas to keep it running, still no codes. any ideas?

Why did you replace the alternator? You stated all this started happening after you replaced the alternator. Might want to go back over your work and see if there is anything that was knocked off or pinched when you did the alternator. If everything looks good, what is the voltage at the battery terminals with the engine running?

I thought the alternator was bad, how i always checked this on other cars was by removing the positive cable and it should continue to run.. but this car did not... i replaced the alternator and it still died when positive is removed and i had the old one tested and it was fine. im getting 14.4 at the battery at idle it will jump to 14.8 which i tihnk is high, @ 2500 ^. this all actually happened a step after the alternator.. i noticed the wireing harness to the injectors were shot, dry rot and falling apart so i got one from a junk yard to replace it really common problem for these cars i guess took awhile to find a good one. then the next start up is was idling rough. i cant tell if its because of to much fuel or to much air. i also read that the cts or ambient temp sensor being bad could cause it to run lean. but like i said im not getting any codes.

i always checked this on other cars was by removing the positive cable and it should continue to run.


Whoooowwwww.............. Never, ever do that again. That is the fastest way to fry every computer in your car.

well im 24 and have been working on foreign cars for about 7 years now and have never had this problem until i came across a POS american car.

You can fry a foreign car the same way, just as fast.

ok this still doesnt help my situation. my ecu is not fried, this car is running to lean or to rich and its a sensor or somthing like i said ive heard it could be a temp sensor or sometihng. anything other then telling me i freid something i know i didnt would be much appreciated.

How do you happen to be so certain what isn't bad when you don't know what is? You very well could have damaged the ECU permanently. Just because the car will run doesn't mean the ECU isn't damaged. Most people think of a fried one meaning stone cold dead, but usually its smaller individual circuits, like capacitors that control the injectors or transistors that engage other controls that get damaged by the voltage spike caused from someone disconnecting a battery while its running. Also, it doesn't matter one bit if its American or Japanese, most parts for both are all made in Taiwan anyhow.

If you think its a lean or rich condition, hook up a scanner that reads data pids and see what the O2 voltage is. Or chase down someone with an oscilloscope and monitor it directly at the sensor. If you think its a temp sensor, put a multimeter on it and see what it reads in comparison to actual engine temp. Don't guess at it, test it. I have a feeling its not a sensor.

im going to check the voltages on the sensors tonight but last night i found out the car ran fine after i heated my garage up to 77 degrees. and will stall when its cold.

Which sensor voltages are you going to check out? Take a look at the engine coolant temperature sensor voltage. Also inspect the ECT connector and make sure it isn't all green.

tested all my major sensors all read fine except ect which stayed at .04 never changed with temp change. i tried running car with it disc. and there was no difference with the idle just the fans ran on high. i pulled the ecu and will be replacing it as soon as i can. i sure hope this is the fix, idk where else to look.

If you unplug the coolant temperature sensor and check the voltage in the connector on the white/green wire, you should see 5 volts with the ignition on. Do you see 5 volts? Unplugging the temperature sensor should also set a trouble code in the ECA. Is there an ECT trouble code stored? If you were back probed in the sensor connector on the brown/green wire trying to monitor ECT voltage, you were reading the ground side of the sensor which should be around 0.1 volts. You need to be back probed into the white/green wire to see ECT voltage.

Obviously the ECT wire to the PCM is good because the PCM turned on the coolant fans when you disconnected the sensor.

i dont have a brown wire i have a black and white and a green and white. the black is a constant 12v ground and the green is suppose to be a signal wire to the ecu im guessing. with the sensor plugged in and key on i put positive probe on the green and negative probe on neg of battery and thats what gave me the .04 volts.

put in a known working ecu and still have the same problem. so heres my question. since the care will run better with the maf sensor unplugged (yes i replaced the maf sensor) what does unplugging the maf sensor do? since no sensor is it running more or less fuel as a default?


note - is it possible to reverse the 2 wires for the ect? this was replaced by someone else not to long ago, i wouldnt think it would matter since its dc but does anyone know for sure?

It forces the computer to use default values.

i understand it does that, as i said in my post, but what are the default values. more or less fuel

It uses an average, probably less when cold and more when hot. The MAF feeds important data for the computer. If it ran well without it, they wouldn't put it in there. They just programmed a "limp in" mode so you won't be stuck in case of a failure.

Update*** Ok was really getting tired of meesing with car so i rechecked all of the sensors that have anything to do with fuel or air control and i think the new maf sensor i purchased is defective.. the + signal out to ecu is reading 0.04 volts and its suppose to have a baseline of 0.7-1.0 so im going to return the maf for a new one and ill post results.

Okay, so i finally found the root of the problem, and to all the ppl that tried to help but never suggestion this must be backyard mechanics. my IAC valve or idle air control was stuck open and needed replaced, bought a new one and she runs like a charm now.

and to all the ppl that tried to help but never suggestion this must be backyard mechanics


You're the idiot that couldn't explain the symptoms right. Like anything else........ "Garbage in....garbage out" Don't bother ever coming here for help again.

Glad to see you figured it out. IAC problem would definitely cause a stalling issue. Thanks for the follow up on this.


Closed as solved.