Radiator fan

A lot of radiators are so efficient they give up the heat with just a little natural air flow. The place to start is by connecting a scanner to view live data and see what the Engine Computer is seeing for coolant temperature. Chrysler fans turn on at 210 degrees. Many GM vehicles don't turn on the fans until around 220 degrees. Other brands fall within that range. You can also use the scanner to command the fan on to test the control circuit.

You can also try disconnecting the coolant temperature sensor while the ignition switch is on. With Chrysler products that will make the fan turn on because the Engine Computer doesn't know if the engine might be overheating. That will set a diagnostic fault code too and the Check Engine light will turn on but those will reset on their own. There's usually two coolant temperature sensors. The single-wire sensor is for the dash gauge. You want the two-wire sensor for the Engine Computer.

Chrysler never did anything with Hyundai. I just used them as an example. Sorry that I didn't clarify that. The only thing they have in common is Hyundai, Toyota, and Chrysler are the top three manufacturers in the world when it comes to customer-friendly business practices, at least according to one high-level national trainer.

All electronic fuel injection systems work nearly the same way. If you want to look for the coolant temperature sensor it has to have two wires because the ground return wire is where the computer monitors that it is connected properly. Most cars that have a temperature gauge on the dash use a different sensor for that and it only needs and has one wire.

To add to the confusion, there are three different possible sensors for your car. If you find a single-wire sensor you have to keep looking for a two-wire sensor. You could also have a three-wire sensor that incorporates both of them together.

When we're looking at the cause of a dead cooling fan there are actually three circuits to consider. The first one is the sensing circuit. The second is where the computer turns on the relay, and the third is the high current to the fan motor that is switched on and off by that relay. On most cars the computer will turn the fan on when the sensor is disconnected. That is because there is no way to know how hot the engine is or if it's overheating, so they run the fan just in case to be safe. The quick test is to unplug the sensor. If the fan turns on you know the high current circuit is working, the motor is good, the relay is okay, and the computer has control over it. That also tells you the wiring for the sensor is okay when the fan turns off shortly after the sensor is reconnected.

I can't find any reference to the fan relay so I don't know if it's an electronic module for variable speed control or if it's a standard relay. There are a number of fan motors available too. Some have four wires indicating they are two-speed motors and will not use a speed control module. If you have a fan relay under the hood, or a low-speed and a high-speed relay, feel if they click when you unplug the sensor. If they do but the fan doesn't run it is usually because the motor is tight and it drew excessive current and blew a fuse.