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We have a new OTC 3209 scanner. Has anyone ever used one to see what was happening when the above code goes off? We know thermostat is the most obvious but we are getting good heat. The code doesn't go off for a week after we reset. Last time we reset we had a few days of extremely cold temps (-2) and it was good but then went off a week later again when temps were actually in the 30's. Before digging into the thermostat wanted to verify what is going on? Possibly an intake air sensor or ECT or something else in the wiring. Seems like issue started after removing engine cover to inspect plugs?
 

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I figured out to access the freeze data with my scanner. It showed that when the P0128 code was activated the car had been running 16 mins. Speed was 58. Ambient temp 34f. Air Intake 68f. Coolant temp 141f.
 

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I figured out to access the freeze data with my scanner. It showed that when the P0128 code was activated the car had been running 16 mins. Speed was 58. Ambient temp 34f. Air Intake 68f. Coolant temp 141f.
That's the coolant temperature sensor which is screwed into the thermostat housing. You can get the entire housing with the sensor and actual thermostat for about the same price as the sensor itself so I opted to just replace it all. At least at the time the price was about the same, can speak for today.

Mine is always 180-190 degrees by the time I hit highway one. When that sensor went bad it got stuck at 167 and stayed there for the rest of my 20.4 mile commute, but heat worked fine. I'm also assuming the thermostat opened on que as well since it all seemed to be normal except that reading.
 

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I’m actually having this issue myself. I haven’t freeze framed the code but I’m trying to find out if it’s the sensor or the thermostat. The gauge needle goes to its normal spot, not low and I get good heat from the vents. I’m probably going to do a resistance test on the sensor to see if it’s got a short or something. Anyone have a similar issue and were able to rule it as the sensor?
 

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One of the common things that happens to a thermostat with age is that it does not close completely or it opens too quickly. When that happens, it takes longer to get up to operating temp. It does get up to temp which is why it has heat and the gauge looks normal.The code is telling you it's cold too long.
 

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Well I guess I might as well just change the whole thing out, just about to roll over to 110k on it. I watched some videos and that lower rear bolt looks to be a real PITA to remove and put back. Not looking forward to it
 
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