Vehicle won't blow hot air. The fan works, but only cool air regardless of the temperature setting

What makes you thing it's a sensor ? A lot of thing's could cause this , taking the vehicle to a qualified repair shop is what should be done. They will do a full system scan .
ENGINE HOT A/C OFF
Cooling System Description and Operation

Coolant Warning Messages
The radio will display the following messages if the following conditions exist in the cooling system.
• Engine hot--A/C OFF will be displayed if coolant temperature is above 117°C (243°F). For imports 115°C (239°F).
• Engine coolant hot--Idle engine will be displayed if coolant temperature is above 118°C (245°F).
• Engine overheated--Stop engine will be displayed if coolant temperature is above 123°C (253°F).

Cooling Fan Control - Two Fan System
The engine cooling fan system consists of 2 puller type electrical cooling fans and 3 fan relays. The relays are arranged in a series parallel (S/P) configuration that allows the engine control module (ECM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block. The ground path is provided at G104.
During low speed operation, the ECM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan S/P relay and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the ECM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the ECM supplies a ground path for the high speed fan relay and the cooling fan S/P relay through the high speed cooling fan relay control circuit. This energizes the cooling fan S/P relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time, the high speed fan relay coil is energized closing the relay contacts, and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit, to the right cooling fan. During high speed fan operation, both engine cooling fans have their own ground path. The result is a parallel circuit with both fans running at high speed.
The ECM commands the low speed cooling fans ON under the following conditions:
• Engine coolant temperature exceeds approximately 94.5°C (202°F).
• A/C refrigerant pressure exceeds 1447 kPa (210 psi).
• After the vehicle is shut OFF, if the engine coolant temperature at key-off is greater than 101°C (214°F), the low speed fans will run for a minimum of 60 seconds. After 60 seconds, if the coolant temperature drops below 101°C (214°F), the fans will shut OFF. The fans will automatically shut OFF after 3 minutes, regardless of coolant temperature.
The ECM commands the high speed fans ON under the following conditions:
• Engine coolant temperature exceeds approximately 104.25°C (220°F).
• A/C refrigerant pressure exceeds approximately 1824 kPa (265 psi).
• When certain DTCs set
At idle and very low vehicle speeds the cooling fans are only allowed to increase in speed, if required. This ensures idle stability by preventing the fans from cycling between high and low speed.

DTC P1258: Engine Coolant Overtemperature - Protection Mode Active

Did you check the fuses, any voltage at the fuses? In the picture, the left side of relay is control, the pcm grounds the control side of relay. Any applicable trouble codes? Check the coolant temp sensor. I'm not saying replace anything. Will the fans come on if you turn on the ac?
The fans should come on around 220 degrees F. Some makes and models, if you unplug the coolant temp sensor, the fan/s may run all the time? The info I looked at was for 1500--5.3L engine--non-hybrid.

Temperature Warning Light is on Inspection Service How this system works: With the exception of older, air-cooled vehicles, cars rely on a liquid called coolant (or antifreeze) to keep the engine at an optimal temperature. Coolant is a mixture of water and ethylene glycol, and it circulates around the engine block and absorbs excess heat, which keeps the engine from overheating. The coolant converts that heat to air in the radiator, and then the air is emitted, at which time the coolant is ready to absorb more heat. Without coolant, the engine would quickly ruin itself with its own heat production. Common reasons for this to happen:

• Coolant is low or weak: The most common culprit when an engine overheats is low or weak coolant. If your car doesn't have enough coolant, then it can't absorb enough heat. While your car will naturally lose small amounts of coolant over the years, a leak is the most likely cause of low coolant levels.The proper ratio of coolant to water can also get distorted, resulting in a problem. Too little or even too much antifreeze can dramatically lower the boiling point of the coolant. A proper ratio of antifreeze to water is 50/50 to 60/40, depending on the vehicle.
• Broken radiator fan shroud: The radiator fan shroud directs the airflow across the radiator so the air can absorb the coolant's heat. When the fan shroud breaks or becomes dislodged, air fails to enter the radiator, and the coolant will no longer have a place to direct the transfer of heat.
• Broken or missing air dam: Along with the shroud, some vehicles have an air dam (or deflector) underneath the vehicle. If this is broken or missing then the air can pass underneath the vehicle but not also through the radiator, which will cause overheating. These air dams are essential in newer vehicles, as they force the air through the fan shroud.
• Faulty coolant temperature sensor: The temperature sensor takes constant readings of the coolant temperature and sends that information to the engine control unit. Based on the temperature of the coolant, the engine control unit adjusts the ignition timing, the fuel injector pulse, and the operation of the electric cooling fan.
• Bad water pump: The water pump is responsible for keeping the coolant cycling throughout the engine. After the coolant transfers its heat energy to the air, the water pump recirculates it around the engine so that it can absorb more heat. The most common water pump problems are a leaking pump, bad bearings, or an impeller that has rotted away due to a low coolant ratio.
• Stuck thermostat: The thermostat acts as a dam for the coolant. When the engine first turns on, and it is still cold, the thermostat keeps the coolant from circulating, which allows the engine to warm up as quickly as possible. Once the engine has reached its operating temperature, the thermostat opens and allows the coolant to circulate. A stuck thermometer may stay permanently sealed and therefore keep the coolant from reaching the engine block.
The thermostat may also stick open. This will not usually result in overheating, but it will waste gas.

• Broken engine cooling fan: The engine has a cooling fan that is deployed when the coolant needs some extra help. When the coolant temperature sensor notices that the coolant temperature is getting too high, the engine control unit (on newer vehicles) will initiate the cooling fan to reduce the temperature.
• Broken thermostatic fan clutch: Older vehicles use a thermostatic fan clutch to engage the engine cooling fan, which is mounted to the fan blades. The fan clutch uses a bi-metallic spring that tightens when the temperature increases. This acts as a "high speed" option for the fan, and when engaged, it draws more air across the radiator.
• Blown head gasket: The head gaskets sit between the engine block and the cylinder heads, and keep coolant from entering the engine's oil and combustion chamber. When a gasket blows and coolant seeps in, the issue is not only that the engine will overheat, but also that damage may be done to the catalytic converter and oxygen sensors due to contamination from the coolant. What to expect: A top-rated mobile mechanic will come to your home or office to determine the cause of the temperature warning light turning on and the source of the overheating, and will then provide a detailed inspection report that includes the scope and cost of the necessary repairs. How important is this service? An overheating engine is extremely dangerous. It is not safe to drive a vehicle with an overheating engine, or you may ruin the engine completely and put yourself at risk. As soon as you notice the light come on, pull over. If there is no place to safely pull over, turn off your radio and other electrical units, and turn your heat on high (this will funnel some of the hot engine air into the cabin). As soon as you can safely pull over, do so, and then book one of our mechanics to perform an inspection.
  

It sounds like your cooling fan(s) are not working. Most vehicles run the cooling fan full time when the A/C is on so that air is always being drawn through the condenser. If the A/C is not on, then there is a coolant temperature sensor that should activate the fan(s) when the temperature reaches a specific temperature. It will cool down when the vehicle is in motion because the forward motion of the vehicle forces air through the condenser and radiator assemblies. You need to check the fans and the fan circuit for problems since they don't seem to be working in for either A/C or temp sensor.

You could have a faulty engine coolant sensor or intake air temperature sensor. Fuel injectors clogged or dirty flooding engine.
Clean fuel injectors, replace fuel filter and air filter, and see if the problem persists.
If it does ECT sensor is bad. If CMP sensor was bad, the vehicle won\'t start whether cold or hot. CKP senso and CMP sensor work together if either one fails, the vehicle won\'t start. Have the vehicle code scanned.

Air can be purged. While your engine is cool remove radiator and reservoir caps. Place funnel in radiator. Turn heat to the highest position and start vehicle. Add coolant to radiator as needed while vehicle warms up. You should see bubbles coming out of radiator. Fill reservoir to between cold and hot fill lines. Replace caps when bubbling stops but before coolant temperature reaches normal operating temperature. Never remove the radiator cap until engine has fully cooled down.

a malfunctioning coolant temperature sensor will often send incorrect information to the vehicle's on-board computer. As a result, when the vehicle reaches a normal operating speed the sensor may relay an incorrect signal to the computer that the engine is overheating resulting in engine shutdown. The vehicle will not be able to start again until the engine has completely cooled. also check coolant level and make sure the coolant radiater fans are working. check for any leak in coolant system, that would cause car to overheat.

Sounds like your cooling fans on the radiator are not working. The fans are activated by a thermol switch on the engine or radiator reading the coolant temperature and an A/C switch. When the coolant is too hot the fans should activate cooling the system down. And, when the A/C is on the fans should also activate in order to cool the condensate so the A/C would work.

When you are driving, the movement of the vehicle throught he air is providing enough air flow to keep things cool and functional.

I would check the radiator fan fuse or fuses first. If those are OK I would try to run the fans with 12 volts and a ground that I supply just to see if the fan motor(s) actually run when powered. If the fan don't run when powered then the fans are bad and will need to be replaced. If the fans do run when you power them manually, then something is not allowing the power to activate, like a relay, control unit, or wiring.

It will take a little diagnostics, but it is not too difficult to chase it down.

Heater control valve malfunction will not cause engine to overheat unless coolant is leaking externally...Overheating going down the road can be the result of a few different things...Partly clogged radiator...Insufficient air flow due to possible fan problem...External coolant leak...Make sure fans are operting properly and have cooling system pressure tested for leaks...Gaining and losing heat on the inside of the vehicle usually means system is low on coolant but you must find out where coolant is going

Hi!
It appears we have an Air lock scenario and you will need to perform a system Bleed.
Park the vehicle on level ground, when cold remove coolant filler cap, start engine and leave to idle, turn heater on full and blower to max. When engine reaches operating temperature watch and listen near coolant filler, keep clear as gurgling and hopefully a boil over should occur. Top up with very warm coolant and wait as it may do it again.
Check for heat inside vehicle if warm replace coolant cap but keep an eye on temperature gauge as the ~Air lock may have moved on from heater matrix/core so proceedure needs to be carried out again from COLD.

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