Coolant temperature sensor

[Coryb]

Thanks rabbit, I have put 2 brand new sensors in and still get the same reading on the code scanner. What do you mean by a bad signal.
Here is what my car is doing, maybe you can help me,

I had it on the scanner and it said that my coolant temperature sensor was bad, it was saying high circuit voltage and the computer was reading the car to be at -40 degrees even though it is completely warmed up, so I replaced the coolant temperature sensor twice thinking I may have gotten a bad part but nothing changed. The car starts fine when it's cold but if you shut it off after it is warmed up and try to start it right away, it cranks many times before actually starting and when it does start it spits and sputters and the idle goes up and down between 200rpm's almost stalling and then up to around 3000 rpm's before smoothing out after a few minutes due to the sensor reading -40 so the car pumps more fuel and makes it hard to start. My temperature gauge reads normal until you shut the car off, then when you restart the temperature gauge stays down on cold even when the car is already warmed up, but after about 2 to 3 minutes the gauge comes up to normal. I have good heat and it never over heats.

[xintersecty]

Thanks rabbit, I have put 2 brand new sensors in and still get the same reading on the code scanner. What do you mean by a bad signal.
Here is what my car is doing, maybe you can help me,

I had it on the scanner and it said that my coolant temperature sensor was bad, it was saying high circuit voltage and the computer was reading the car to be at -40 degrees even though it is completely warmed up, so I replaced the coolant temperature sensor twice thinking I may have gotten a bad part but nothing changed. The car starts fine when it's cold but if you shut it off after it is warmed up and try to start it right away, it cranks many times before actually starting and when it does start it spits and sputters and the idle goes up and down between 200rpm's almost stalling and then up to around 3000 rpm's before smoothing out after a few minutes due to the sensor reading -40 so the car pumps more fuel and makes it hard to start. My temperature gauge reads normal until you shut the car off, then when you restart the temperature gauge stays down on cold even when the car is already warmed up, but after about 2 to 3 minutes the gauge comes up to normal. I have good heat and it never over heats.

Rabbits right, either bad sensor or bad signal. Since you have a spare sensor, is a two wire? If so you can measure it and it give you known resistance vs. temp. I don't have a chart handy. You can also check it with boiling water if you have the chart. That should tell you if your sensor is good and maybe your signal bad. If it's a bad signal, a fault in the wiring can do that same error. I don't have my car or books with me as I am traveling for work.

I would really check that wiring and make also make sure it's putting out the right voltage too. V = IR

[Coryb]

Rabbits right, either bad sensor or bad signal. Since you have a spare sensor, is a two wire? If so you can measure it and it give you known resistance vs. temp. I don't have a chart handy. You can also check it with boiling water if you have the chart. That should tell you if your sensor is good and maybe your signal bad. If it's a bad signal, a fault in the wiring can do that same error. I don't have my car or books with me as I am traveling for work.

I would really check that wiring and make also make sure it's putting out the right voltage too. V = IR

Wouldn't a faulty wire cause the temperature gauge to stop working completely? My temperature gauge works properly on a cold start, slowly climbs to normal and stays there but as soon as you shut the car off and immediately turn the key to the on position, the gauge should rise to normal right? Mine stays on cold until you run the car for about 2 to 3 minutes then it returns to normal and is fine again till you shut the car off.

[xintersecty]

Yes you have written the pattern of your fault three times in the thread. So we have paid attention. A faulty wire can cause the sensor to fail COMPLETELY or PARTIALLY. Either you have a bad computer or a faulty wire. If you have a volt meter measure the sensor at the connector. Besides you did not answer the question is a two wire sensor? If so those work off of resistance. If a four wire, it's current.

So by replacing the sensor you proven there might be a possibility of a partial fault. And besides your mechanic should be saying all this too. So until you proven that the signal out of the computer to the connector is good, then it's an unknown and might be the cause.

So it could be a bad ground, a bad computer, a vacuum leak, bad something else that I did not think about.

[Coryb]

Yes you have written the pattern of your fault three times in the thread. So we have paid attention. A faulty wire can cause the sensor to fail COMPLETELY or PARTIALLY. Either you have a bad computer or a faulty wire. If you have a volt meter measure the sensor at the connector. Besides you did not answer the question is a two wire sensor? If so those work off of resistance. If a four wire, it's current.

So by replacing the sensor you proven there might be a possibility of a partial fault. And besides your mechanic should be saying all this too. So until you proven that the signal out of the computer to the connector is good, then it's an unknown and might be the cause.

So it could be a bad ground, a bad computer, a vacuum leak, bad something else that I did not think about.

I'm sorry for all the confusion, and to answer your question yes it is a 2 wire connector on the temp sensor. Can I check the sensor with an ohm meter, I don't own a volt meter.

[xintersecty]

I'm sorry for all the confusion, and to answer your question yes it is a 2 wire connector on the temp sensor. Can I check the sensor with an ohm meter, I don't own a volt meter.

I found a multimeter that should do everything you need: http://www.amazon.ca/Digital-Volt-Me...rds=volt+meter

Here is a coolant sensor chart I found at autozone. It should be close enough:


If you noticed the -40 value is the highest resistance which be the same as an open circuit.

You should check the voltage on the computer side. I am not sure if they run +5 volt signal or +12 volt signal. You can put your volt-meter on the circuit and do the on/off with the engine it should stay consistent the entire time.

[petrified.rabbit]

You have a bad connection somewhere. When it is open, you are reading -40, when the wires contact you get proper reading.

[Coryb]

Hey there, would this multimeter work also? I don't have an amazon account but I do have an eBay account.Digital LCD Multimeter Meter Tester Voltmeter Ammeter Ohmmeter Volt OHM Test | eBay

[xintersecty]

Hey there, would this multimeter work also? I don't have an amazon account but I do have an eBay account.Digital LCD Multimeter Meter Tester Voltmeter Ammeter Ohmmeter Volt OHM Test | eBay

It will work fine. It's a bit of a haul from Hong kong. Check you local Hardware stores and see if you can find anything locally that's faster. Then again buying tools a personal choice. Just get the tool and learn how to use it.

[Coryb]

Thanks so much for all the great info you have given me, it is really appreciated.