2015 SE 1.6 Overheating @idle +A/C blowing warm air

[hamhawk]

The symptoms are while sitting at traffic lights, or just at idle, the temp will slowly creep up until it hits 230 while the A/C stops blowing cold air, sending the car into limp mode
Switching on the heater to full blast is usually enough to slow the temp climb long enough for a traffic light to change
At 25+ mph, the temperature will drop to 180 within a few minutes from 220

This has become a headscratcher for me. Here is what I have done, and not in any particular order.

Recharged A/C
Replaced Accessory Belt
Replaced Thermostat
Completely Flushed/Pressure Tested Coolant System
Replaced Engine Coolant Temperature Sensor
Ran the gamut of tests available in Forscan using a highspeed autoswitching designed for Forscan OBD2 USB connection

Forscan is currently telling me the new Engine Coolant Temperature sensor is reading wrong but only after the engine on test, there are no DTC's unless it hits limp mode.
In Fact the only current DTC is APIM U3000:04-2b (possibly related? information on this code is unclear and not covered well in the Workshop Manual)
My xTool A30M bidirectional scanner also reports the APIM code (This thing is outstanding)
The xtool A10 has a dashboard feature I use to monitor temp

After replacing the thermostat, the ac works better but not well at idle and now the built in temperature gauge is apparently not working, as my obd2 dash connection has been reading temperature increases that I have verified with an infrared gun type temp sensor, which has me concerned the new engine coolant temp sensor is bad since its also causing a code readable by Forscan.


Current plan - Replace the apparent faulty sensor, examine new belt for slippage (would explain A/C issues, plus it looks like copious amounts of dressing were applied in the past - I'm not the first owner[Enterprise Rental Fleet in San Francisco], but it only has 60k miles, nonetheless I want to clean the whole belt area to remove any contaminate, and might just get another belt), examine and confirm cooling fan operation, check for combustion leaks {head gasket, but no symptoms, however hitting 230 several times makes this possible}

I'm doubtful its the coolant pump because the coolant is moving as I have read temps on all the hoses at operating temps, including the overflow tank, but I'm no expert.
Am I working down the right path? The radiator/hoses might be my next target, if the sensor, cleaning the belt area. and fan end up not fixing the issue.

 

[Pappy]

Could be your radiator fan not working. Check to see if it is turning when the ac is warm

 

[scotman]

Definitely need to confirm that the cooling fans are working!

 

[Handy Andy]

IF the sender is bad, just remove the wire, does the Fan come on?

Then the sender is the wrong one, they are a semiconductor that exhibits a drop per temperature of degree C of change.

The failsafe of the sensor is to "go open" forcing the fan on all the time.

Seen a rash of bad ones lately - Pre - to - Post Covid retooling issues.

So, if no fan, the relay or it's wiring - including the fan - are suspect. You have AC fan when AC is on, so wiring TO the fan should be ok, the Sender to the system, is not...

 

[SyntheticAtmosphere]

Be sure the pulleys are clean, I recently had to clean the ribs in a crank pulley so bad it was throwing belts on a Subaru. Belt would slip, cold squeal and alternator couldnt keep up.