2001 Malibu P0128 error code, problem not thermostat

Hi folks. If you can help us with this, we'd certainly appreciate it. My father is working on my sister's car and has encountered a problem he can't
quite diagnose. He describes it thusly:
2001 Chevy Malibu 3100 6 cyl engine
"Check Engine" light comes on when ignition is turned on and doesn't go off until ignition is turned off. Temperature gauge in dash does not function. Both cooling fans come on immediately after engine is started and do not turn off until ignition is turned off. A test was performed for the "Check Engine" light and an error code of P0128 was indicated.
Engine temperature sensor has been replaced and new coolant has been added. Also, the battery was disconnected and reconnected. None of this has helped. The thermostat is believed to be functioning properly as there is no indication that engine is overheating.
When engine is started it idles at 800 rpms but when the wire to the temperature sensor is disconnected, the rpms increase to 1200. There is no indication that the engine is overheating.
When the ignition switch is turned on, there is no electric power to the 30 amp fuse in the box under the hood for cooling fan #2. Fuses in all 3 boxes have been tested and are good.
Any ideas?
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Malibu Owner wrote:

Hi Malibu Owner...
Not a mechanic, so take what I say with a grain of salt; but I did experience the same fault a few years ago with an Olds 98 for what it's worth...
As soon as I turned the ignition on, both fans came on high, never stopped until the ignition was turned off.
Turned out to be as simple as one of those little blue clips that GM uses (used?) to clip a bundle of wires together. They foolishly have metal inserts in them.
In this case, the wires coming out of the air conditioning pressure switch were clipped together with one of these, and the metal insert had chewed through the insulation shorting them. Removing the clip fixed it up perfectly :)
Take care.
Ken
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Ken,
Thanks for the help. My father looked for the problem you described, but wasn't able to find any evidence of it.
I have googled the whole shebang, of course, and some of what I've read seems to say that the scan tool (the machine they use at the auto parts store to detect the error code) has a function that allows it to clear the code and that, once this this is done, the fans will stop running continuously. We did try disconnecting the battery in an effort to clear the code, but it didn't work; maybe the scan tool can succeed where the battery disconnect failed. My father doesn't think the scan tool has that function and so isn't pursuing that option. We'll see what happens.
But again, thanks for the help.
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The computer will automatically run both fans continuously if it can not read engine temp correctly as a precaution. You said you replaced the ECT sensor, I would visually inspect the connector and wiring as well as checking continuity between the sensor and the ECM. The computer is not seeing is for some reason. By the way, this would take a dealer tech about 15-30 minutes to diagnose, save yourself the hassle and take it for a diagnosis...
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