Hi guys I'm new here I have been doing some research as of lately to try and figure out what is wrong with my 02 civic lx. I guess you need the car specs first. All stock except the k&n drop in air filter I have. 144000 miles no leaks no drips just changed to full synthetic abut 2-3 weeks ago.

About 3-4 days ago coming home from work I turned on the car let it warm up for about 5-7 minutes got in started to drive away and than the engine light popped up. Once I got home I plugged in my obII reader and it gave me the code of p0128. On the way home the car was running fine no overheating nothing out of the ordinary. S once I got home I cleared the code and than 2 days later it popped again. This time I got a new thermostat from autozone and some coolant that I miked 50/50 myself. Drained the radiator removed the old thermostat installed the new one and I thought all was fine till this morning. I started the car it warmed up for about1-2 minutes and than I took off I was running late about a half a mile it popped and again same code I took my reader with me just in case. Leared it on the road.

When I got home I did Some reaserch and I did not turn the heat to on full. So when I got home I turned on the heater waited for the fan to kick on twice filled it up and capped the radiator. I siphoned the resivoir and put in clean fluid.

The coolant gage reads 1-2 lines below half way. Idles fine no smoke runs great.

This is also what i did...

The electric sensor on top of the thermostat when the engine was warm I unplugged it andyup the engine light came on no surprise, than I loosened the sensor to try to drain any air out of the system tightened plugged in the sensor cleared the code.

I Also drained about 2 cups from the radiator a added straight water since water is a better conductor of heat then the glycol.

What I think I have left...

I could install 2 new sensors but I read they don't have a high fail rate..?

Try a new thermostat ..?

I also found out that there is Ecu update I called 2 honda dealers the local one said there was a update and would cost 105.00 to do but could not tell me if my car already had it done. The second dealer is where the previous bought the car I called them gave them the vin and couldn't find anything abut an update. I even gave her the bulletin number no luck...?

That's my issue I know I'm new here but I would really appreciate the help !!

Tony