Why would the radiator fan not work on a 2002 Jeep Grand Cherokee Laredo?

Answer 1

You can figure it out. Here's some general information. It's probably a bad fuse (in the fan circuit or in the sensor circuit if the latter is fused separately), a bad relay, or a bad fan. Here's how the fan works. There is a heat sensor that operates the fan relay. It is located where it can sense coolant temperature. And it is the fan relay that turns the fan on and off according to the directions it gets from that temperature sensor. A relay is a switch (yes, just like a light switch) that is electrically controlled. There is a circuit that goes from the fuse panel to the sensor and through that to the control side of the relay. There is another circuit from a fuse to the fan relay and then to the fan itself. That's right, two circuits to the relay. There may be two fuses, or both may be fed from one fuse. But there are two circuits - two places for the 12 volts to go. One is to the control side of the relay through the temperature sensor, and the other is to the relay's contact set and to the fan. You already know the temperature sensor has to be hot to trigger the relay and tell it to turn on the fan. The sensor will be electrically "open" when the coolant is not hot. (The sensor has a "trip point" at which contacts in it close.) There are fuses in the fan relay circuit that need to be checked 'cause it's easy to check them. Don't be faked out. Be sure the fuse is good. If you have a little meter, use it. If you have a little test light (like an ice pick with a hollow handle and a wire coming out the end with an alligator clip on the end which you clip to ground), use that. Don't be afraid to get dirty. Just use your head and think things through. Work safe and work smart. If the fuse is good, move on. You'll need to use your meter or test light to see if there is 12 volts to one side of the temperature sensor. There won't be anything on the other side if the vehicle is cool. The sensor has to be hot enough to "close" and trigger the relay to tell it to turn on the fan. But you knew that. You'll have to figure out which of the relay wires are the ones to the contacts and which are the ones to the control circuit. Usually the wires to the contact set are heavier. If any of this sounds like Greek, don't try it. That's rule number one. Get some help to sort it out. Get a "motors manual" on your vehicle. They are a bargain, particularly if you are planning on keeping the unit. And there are a number of things you can do (like troubleshoot a fan and fan control circuit) yourself that are nearly impossible without the kind of help the reference can provide. Used bookstores and eBay have these books. Even a new one from a big auto parts chain is worth the investment. You'll be looking in the electrical section at the diagrams and the troubleshooting section. Your library sometimes has repair manuals on the shelf (or, more probably now that it's the 21st century) a computer with the stuff in a central location which will allow anyone on the system to look at it. If this is the case, fire up the laser printer and shell out whatever the going rate is for copies and take your work home with you. It's another bargain. Getting help was suggested. Find someone who speaks "automotive" and get them to help. You already know someone. The trick is to "sign them up" to help you with this problem. Good luck.