My computer runs uncommonly slowly at times, so when I click on "Reply", nothing happens. I assume I didn't hit it squarely so I click on it again, then end up with two or three multiple replies. We've all seen that enough that we don't pay any attention any more.
'03 was right in the middle of when they were switching from using two coolant temperature sensors to a single one. If you have two, the one with a single wire is for the dash gauge. Ignore that one. The sensor for the Engine Computer will always have two wires. Unplug that one while the ignition switch is on. That will set a diagnostic fault code and turn on the Check Engine light, but it will also force the computer into turning on the fan relay as a safety measure. If that happens, the system is working and all that's left is that sensor, but failure of those is extremely uncommon except for a rash of failures on early '90s Ford products.
The next thing is to use a scanner to view live data and see what coolant temperature the computer is seeing. On older models Chrysler turned the electric fans on at 210 degrees, and off at 198 degrees. Most GMs didn't turn on until around 222 degrees. Most of the newer Chryslers are up to around 216 degrees now. If you see the temperature get over 230 degrees, the fan should have been running by then.
If the fan doesn't run when you unplug the coolant temperature sensor, feel if the relay is clicking on. If it is, the sensor circuit and low-current side of the relay is working. Also, under the "Inputs and Outputs" menu, the fan relay will be listed as "on" or "off". If it's commanded on but the relay didn't click, there's not much to that part of the circuit to look at.
You can also use the scanner in "ATM", (actuator test mode), to command the computer to turn on the relay. You'll be able to hear it click on and off about once per second. The fan should by pulsing on and off at the same time. If the relay does click on, it could have burned contacts, but since you already replaced it, the more common failure is the motor is tight which will make it draw high current, and that will blow a fuse or burn open a fusible link wire. By '03 you should have a plug-in fuse for the fan, typically a large 30 or 40-amp cartridge fuse.
The fastest way to tell if the fuse is blown is to unplug the relay, then test for 12 volts with a voltmeter or test light. I prefer the test light because it responds faster than a digital meter, and it's more accurate. I have an entire page on my web site devoted to the 12 volts being there when tested with a digital meter but not with a test light, and the circuit doesn't work. In this case the story is from helping a very experienced co-worker who wasted half a day on a K-car in the early '90s, and the problem was a dead new fan motor.
At this point you don't have to worry about which terminal is which in the relay socket. Only one will have 12 volts all the time, and a second terminal might have 12 volts when the ignition switch is on. If you don't find 12 volts on any terminal, the fuse is open.
I also have an entire story about my '88 Grand Caravan running too hot but only over 60 mph at first and only when the outside temperature was over 60 degrees. Toward the end that was down to 30 degrees outside and at any road speed. The cause was the cooling fins on the radiator were corroded away like rotten chocolate chip cookies. New radiator solved that. I never paid attention to whether the fan was running because the overheating occurred while driving, so natural air flow made the fan unnecessary.
Most people don't have a scanner at home, and simple code readers won't do the tests I listed. You might be able to borrow one from an auto parts store that rents or borrows tools, otherwise you'll need to find a mechanic. I have a Chrysler DRB3. A lot of independent shops bought them because with an extra plug-in card, they will do emissions-related tests on any brand of car sold in the U.S. Starting with '96 models. The '04 Durango / Dakota were the first models it was obsolete for. It worked on some models all the way up to 2007, but it worked on all Chryslers in 2003. Other brands of aftermarket scanners will work for this too. They never do as much as the manufacturer's stuff, but they work on more systems on all brands of cars.
Wednesday, June 15th, 2016 AT 10:06 PM
