Thanks for using Just Answer, if the cooling system has air pocket in the system, it will also give the PCM (Powertrain Control Module) a false reading, and therefore throw a code, also when using teflon tape on threads, too much and you can also get a false reading. Try hoisting the front of the car so the radiator is the highest point on the engine, and try to burp the system while the car is running and the radiator cap is open, be sure to maintain coolant level.
The sending unit only sends a signal to the gauge, and the ECT sends a signal to the PCM.
Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature sensor signal is used by the powertrain control module to modify ignition timing and the air-to-fuel ratio.
DTC P0125: CHECK ENGINE COOLANT LEVEL
Diagnostic Trouble Code (DTC) P0125 indicates the ECT sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting engine. This DTC will light the MIL.
Is the engine coolant level fill correct?
Click below for testing, See Section C
CLICK HERE FOR SENDING UNIT TESTING
You are welcome, and yes ramps would be perfect.
Yes you want to run the car with the cap open, otherwise the air will remain trapped, you can squeeze the radiator hose to hurry the process. And yes it is safe.
You will need to maintain coolant level by adding coolant when needed, when the "burps" the coolant level may drop.
About how long does the burping process take and how will I know when it is enough? I've never 'burped' a coolant system before, does it make some sort of noise so I know that air is being let out of the system? How long can I leave the radiator cap off because won't coolant overflow out of that hole after awhile? If necessary, do I add coolant directly to the radiator during this process and do I try to keep the coolant level in the radiator topped off? I apologize for so many detailed questions, I just want to know exactly what I'm supposed to do. Thank you for your patience.
When the car is cold the coolant in the radiator will stay dormant, until the coolant in the engine warms up and the thermostat opens allowing the coolant to begin to flow, once that happens and you will notice the coolant begin to flow and move and start circulating, it will force the air pockets that are trapped in the coolant, and engine to the surface. Once the coolant is flowing and starts overflowing, then cap it off.
Last night, I burped the system using your instructions, and tried driving the car to see if it had any effect. It took about 15 minutes of highway driving and another 15 minutes of city driving to get it off of the cold mark on the gauge, but it did eventually go up to the halfway point between the C and H. Today I drove for about 30 minutes city and highway and it never rose above the C until I let it idle in my garage for another 10 minutes after that first 30 minutes. Would it be possible that cool air blasting through the engine compartment when driving at high speeds would have such an effect on the coolant temp reading that it would never get much above the C? Last night when the needle was at the halfway point between the C and H, I felt the radiator hose and it was very hot to the touch, and today when it was only at the C after 30 minutes, the hose was noticeably less hot, but still hot nonetheless, so it seems that the gauge is not giving me an entirely false reading but I would think the gauge would have read higher than it actually did. These results have happened before periodically BEFORE I burped the coolant system, typically on days that were not overly cold, and last night wasn't overly cold, so at this moment I'm not yet sure if last night was a fluke that it did work, or if the problem has truly been solved. Based on the info you gave me, along with the workshop manual pages, I will be happy to accept your answer, but I do have one more question. Are the instructions you listed on an earlier answer as to how to test the engine coolant temp sending unit (the test where you put the sensor in heated water and measure the ohms) for the sensor that sends a signal to the gauge or to the one that sends a signal to the PCM? Please let me know what you make of my response and I will be happy to accept you answer. Thank you for your help.
Ok, no problem the following tests are for the sending unit which is for the gauge. To test the ECT for the PCM a NGS (New Generation Star) or equivalent scan tool is required
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Not likely, either a bad sending unit, or gauge, you will need to perform the tests to determine.
The check engine light came on again from the coolant temp being too low. Got the gauge to go up to 1/2 way point after sitting for a few minutes after driving 1 hour, but dropped to C when resuming driving. Still seems to exhibit signs of bad thermostat if it causes ECT sensor to kick the check engine light on, is it possible for thermostat to be installed backwards or any way the coolant can get around the thermostat when it is not open (bad seal)? If that would be the case, wouldn't the coolant always be flowing even when the engine is still cold?
It is unlikely the thermostat was installed incorrectly, but if it is in fact stuck open then you would see the same results you are getting now. Yes the coolant would flow.
I am sending the instructions for the thermostat replacement in pdf format, (CLICK HERE FOR INSTRUCTIONS).
I changed out the thermostat and put the old one back in, and I replaced the O-ring around the thermostat with a new one and the problem seems to have gone away, so I'm not sure if it was the thermostat or the O-Ring, but I thought you may want to know. I am accepting your answer so that you get paid for responding to so many of my questions and for providing instructions for testing and installations. Thanks again for your help.