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Discussion Starter #1
Aside from the coolant temperature sensor, is there a separate fan control sensor. Have replaced coolant temp sensor, but fans are still coming on as soon as engine starts. Displays message that says "engine too hot, A/C off." Engine is not hot. Temp gauge shows 160 and there is no excessive heat from engine. P0128 code, but don't feel like it is either thermostat or water pump.
 

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which temp gauge shows 160?
these engines are designed to run around 210 for emission purposes.
So on the dash- the temp gauge will be in the middle... or 210


When you hookup an OBD reader- and look at the temp.

it should be around 190-200 or so If I recall correctly- while moving around in traffic.


if youre reading 160 from port-- something is not right.
 

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Discussion Starter #3
Still cannot diagnose

Clearing the code turns off the fans and clears the message on the dash. Found what we thought was a leaking (top) hose. Replaced and the ran the car in the driveway until temp got to around 205. Outside temp was cool, so engine temp (as displayed on the dash gauge) would not reach the 210 mark. Fans did not come on. Thought we might have gotten the problem solved. Yesterday (day after replacing hose) fans and message came on again. Engine still not hot. Check engine light does not come on, but OBD code of P0128 is setting. Some coolant missing from reservoir. Suspect that there may be a small leak in the assembly at the end of the radiator, where the top hose attaches. Appears to be plastic! Radiator is still full. Cannot figure out what is being monitored and sending an incorrect code/message. As mentioned in original post, already replaced engine coolant sensor. Could there be something related to it that needs to be checked? Was told by parts guy that they sell a lot of these sensors. Appreciate any suggestions.
 

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I am going from memory here, but I believe that the wiring diagrams show that the fans can kick to high speed due to the a/c pressure switch as well. In other words, if the A/C is running, the fans will kick to high speed. There is an electrical harness that runs to the a/c switch that can get frayed/jostled that can cause this. I had a similar symptom which my garage fixed when they replaced an A/C hose. The fan was on high even with the A/C not running and the harness was the issue, IIRC.
 

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ac high pressure switch I believe may be the culprit
 

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there is a video on youtube of an impala with fans always running on high.
cause-- faulty AC high pressure switch.
 
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