If im not mistaken, is the ECT Sensor just below the thermostat Housing?..P0128B code keeps popin up at the same time my temp gage goes flat and when turning off my car the two electric fans come on..I clear the code and turn my car back on the temp gages jumps back up...weird stuffs goin on..

 

by the way I have a 2000 MC ss..

 

Yes, I do believe the ECT sensor is the one under the tstat housing on the LIM.

 

I'd replace the T-stat, it maybe stuck open, and do a flush while you're at it. Then have someone clear the code for you (although sometimes the PCM, once the problem's gone, will clear the problem it self) and see if that fixes the problem. If it comes back, have the ECT checked for malfunction.

BTW, have you messed around with the PCM or the long term fuel trim? The PCM will throw the code if the trim is over a set #%.

 

Well in the past couple years i have replace the t-stat two times..but that was with cheap *** Auto Zone parts..I have my own scanner, so I can turn it off whenever but dont think its the t-stat because when i turn off the check engine light the temp gage jumps to normal operating temp.. but ya im ill just replace the sensor see if that fixes it

 

Good luck with it!