Need CLT troubleshooting advice

[gboezio]

I'm chasing a (very) intermittent problem, the cold engine light comes on while I drive and I got a 0125 code only (engine too cold for closed loop.)
So I tapped a twisted pair on the sensor connector and hooked it up to a multimeter, reading DC volts while I drive, I can clearly see the voltage going from 2,4V cold to about 0,450V at diving temp.
But when it does goes cold I would expect a High voltage, but in fact the voltage drops to about 0,300, this triggers a high idle (2500), (havent checked the rad fan) and the cold light while in fact I should see the hot light. This happens for seconds to a few minutes and the voltage have no transitions, it jumps instantly, no special condition cause this it happens randomly.
If I short the sensor to the ECU, the voltage goes to 0 of course and trigger the cold light, rad fan and of course the CEL, but no high idle.

My question is if it's normal for a high temp to trigger the cold light since a hot light exist on the dashboard, the voltage is taken inside the ECU from the 5V ref sent toward the sensor, I'm beginning to think that the 5V supply is dropping low, but this won't explain why the ECU trigger the cold light.

I'm lost and start to think that the ECU is going south.
Thanks a lot for reading this and thanks double to submit stuff I could have missed.

[gboezio]

I have set a 150 ohm resistor in parallel at running temp and finally trigered the hot light, so the ECM seem to work normally so far, the only remaining fault has to be on the hot wire between the connector and the point inside the ECM where the 5V and it's resistor meet the signal input, a high resistance in the hot wire or in one of both connectors would send a high voltage input and a lower voltage to my multimeter, now to tap a wire under the big ECU connector sounds like crap, I wiggled the wires around, I may try later to turn the car over with a forklift to see if it helps, if insanity reach it's peak, i'll set the damn thing on fire and buy a freakin car that don't entertain me this much on my (few) days offs.

[Betrivent]

bump in the hopes somebody else can help you.. I haven't a clue

[CTScott]

The resistance decreases as the temp increases (from open circuit = -40C to dead short = 140C), and the voltage on the THW terminal (C20 pin 97) decreases as temp increases.

At about 265 ohms (0.45 volts on THW) it makes the transition from cold (green symbol) to up to temp (no symbol).

[gboezio]

Thanks Scott and Betrivent, mine is switching off the cold light at 1,01V on THW as you said the resistance decrease putting more of the 5V reference to the ground decreasing the remaining voltage
When the problem shows up, I can see the voltage drop and it triggers a cold condition witch should be a high voltage reading, I think that some added resistance between the 5V could cause me to see low at the sensor connector and high at the ECU, will try to get a 26 gauge wire inside the ECU connector, or I will have to wait that the problem become worst or permanent.

[gboezio]

After almost 2 years of having a once in a while cold problem, but it was mostly running fine, lately it happened more and more, ECU started again to throw codes, high idle...
So I took off the ECU and measured resistance between pin 97 and the CLT sensor found that it was bouncing around, I opened the ECU connector since I had resistance to vary by touching this aera, I pulled hard on the wire (when they are broken inside the insulation won't hold), nothing this is a very good wire, I don't have the tool to release the connectors, but now I measure 0 ohms all the time, so I have put it all back together and since then, it runs perfect, I think it may have been a badly crimped connector (insulation not totally pierced), I hate when I don't find evidence of the problem.