Could it be the temperature switch?

 

Dont know. I am learning as i go. Where is it and how do i check it?

 

I do not know specifically on your Van, maybe someone else who knows can tell you exactly but it is sometimes located by the water neck on the engine where the radiator hose connects. But you will have get a manual to know for sure.

 

There is no temperature switch,it's a thermistor.

 

Well thanks, I stand corrected, but where is that located?

 

My guess you have a wiring issue... The relay (the one on the front bumper) is a computer controlled variable resistor that allows fan speed to vary depending on a variety of circumstances. However, with ignition off fans should be off regardless of any other input.

My guess that something is messed up with the wiring. Check pins in the relay connector, are they corroded?

 

The engine coolant temperature sensor or ECT is located under the coil. Haynes says to detach the power steering reservoir and set out of way. Remove the 2 bolts and the nut to detach it. Then remove the coil and then the coil plate. Un plug ect and then remove. It says to drain radiator but if you are quick enough you can just changed it with out doing so and just top off when done.
Of course this is when the engine is cool.

The ECT sends it's signal to the ECU. The ECU sends the info to the gauge on the dash and when hot enough, will signal the fan relay to turn on the fans.
You should recheck the fan control relay wiring, especially if you installed it with out updating the wire harness that is avaiable and or included in the kit. If you used the one in the kit and just crimped The wires, there could be an issue there. I would solder them. The Black and Dark Green wire is the ground. Orange Red is the 12 to fans, dark Blue and Violet is the 12v signal to turn on the relay , Dark Blue With Dark Green is the power out to the fans.
If you installed the relay and did not really attach the base to the frame, it might be blown due to the increased heat build up not being dissipated to the frame.
The relay can be tested off the van with a 9v battery going to ground input and the drk blue violet and with a meter checking for continuity between the other 2 big contacts. Voltage applied should give you continuity and none when the battery is disconnected if working correctly.
If the relay is bad, most likely you have a bad ECU since it controlls the fan on off from the ECT.

If temp gauge is working I would not replace the ECT sensor but it is cheep and you could try just in case.

I go to the ECU being the issue due my experience with an ecu that made my fans run after a lightning strike that fried the ecu on the 03 caravan I use to have.

 

The ECT sure sounds like a switch to me?

Thermistors don't shut on/off.

 

It is a variable resistor or a rheostat according to its symbol so not a switch and not the decoulper pulley either

 

Ok i found the thermistor and have it exposed and ready for change out tomorrow when the parts stores open. I will bring in the relay to check it out as you described. I didn't mention that i have no codes coming up and no idiot lights lit. after further discussion with my wife she said that a while back she came home and parked the van and came inside. A short time later she left to run an errand and the fans were running. When she returned home they were not running when she turned the van off. This is sounding like a bad spot in the wiring harness to me...any other thoughts? Will let you know what i find out after checking the relay. The new relay did not come supplied with new wiring harness btw and the connectors on the existing harness do not look corroded

 

Would unplugging the coolant temperature sensor shut off the fan? If so it didn't and i am left with wiring harness or pcm...or 2 bad relays. contemplating going to a dealer to get OEM relay at this point. I don't have the means or knowledge to check detailed electrical issues...i know enough to fix the power sliding door (which needs to be done again) but that's about as far as i go.

 

You either have a wiring problem or a second defective fan "relay". The reason the thermistor cannot be the cause of your issue is that the logic of the PCM is such is that it won't turn on the fans when ignition is off. PCM controls fan relay by sending a signal to it of varing frequency which is then interpreted by the "relay" as requests for different fan speed. The sensor has no direct intput on fan operation. It is hugely unlikely that PCM went nuts and is generating a wave signal when none is requested.

The problem is most likely at the wiring or fan "relay" level. Note that the fan relay is attached to the bumper re-enforcement with a plastic rivet. It is important that the replacement relay is attached in the same manner. If it is just left hanging it will not have enough cooling and will fail in short order.

 

I will try one more relay before i take it in to someone who can look at the wiring and test everything properly. Thank you for the help. I will let everyone know what the results are.

 

Good luck. You got some good advice from 443k3.3, user97 and others. Sounds like your relay is being activated by a defective circuit on the computer/sensor side or a defect in the relay itself (closed circuit to fans), or power to the fans from another source (unlikely). Some fans are designed run for a few minutes after the engine is turned off. I don't believe yours is though.

I would check power at the computer/sensor side of the relay to rule that source out 100%.

Your Post #12 re disconnecting the temperature sensor - the computer would respond by activating the relay to provide power to the fans (protective measure).

You likely know this stuff already but for those that don't, here is some basic info on how relays control power sources to various items: http://www.autoshop101.com/forms/hweb2.pdf The relay is basically an interface between a switch circuit and a motor circuit. Power may be from the same source or fuse, but the actual circuits are split and independent except for the relay interface, basically a low amperage circuit controlling a high amperage circuit.

 

So i returned to the auto parts store and explained my situation and that i would like to swap the relay i purchased with one from the shelf to determine if it was a relay issue or something else...I plugged the new relay in bolted it down to the frame and re-attached my battery cable and...no fans. I started the van and cranked the air up and the fans came on as they are supposed to. The i turned off the key and...the fans also stopped running. I am still finding it hard to believe that i had 2 bad relays and that is the end of the story. if it isn't be sure that i will return to this thread and let you all know. Thank you for all of your help and suggestions.

 

Bad batch of relays .......... it happens. Ask the store if they have had many returned. They can test your old relay to see if the fan circuit was permanently closed. Also you might want to check to see if your present relay is from the same bad batch.

Two defective relays in a row ........... highly unlikely ........... might be a good time to buy a lottery ticket.

 

Well the issue is that the "relay" in question is not a relay in the precise sense of the word. It is a variable resistor that is controlled by frequency modulated signal sent by PCM. In terms of the design it is most similar to the interior blower speed control modules.

Because of the nature if the device it has a few transistors inside that emit a lot of heat. If the original units were not properly affixed to the bumper support they'd fail in short order.

Also some more complex electronics for Chrysler vehicles tend to fail right away as opposed to the OEM devices. A well known example is cam position sensor for Chrysler 3.2/3.5 engines (LH platform). Aftermarket ones tend to fail within 6 months where OEMs last upwards of 14 years.

If you experience another failure, I'd pull one at a junkyard -- they sell for $5-7 around here.

 

It is not at all unusual to have a new part DOA out of the box today, just didn't happen many years ago.

It took me awhile to get used to this, now I expect it.

 

I make them bench test every starter and alternator before I leave the store and I also after the other day, will not ever leave with a rebuilt brake part before checking to make sire the bleeder nipple will open. Nothing like fixing someones car at 9pm and you can't go back to the store and someone has to have the vehicle to work the next morning!

Might be a new thread to start, what to look for before you leave the parts counter!

 

To elaborate. As mentioned, the fan "relay" is not the mechanical relay of earlier vans (80-90's). It is a solid-state device, using transistors, very similar to the cabin blower "resistor" (also transistors) used in vans with the Automatic Temperature Control (digital display). When solid-state devices fail, they usually fail shorted, so not surprising your bad one was running with the engine off, since it always has 12 V power.

Many here have experienced "blower fan always on high" with ATC, as I did. Since that "resistor module" costs $60 I tried fixing mine by replacing the drive transistor (MOSFET I recall). I even put in a slightly better one (lower on resistance) and cut slots in the cooling fins. It worked for ~1 yr then "blower always high" again. I finally bought a new module with the round pins (new design).

I haven't fooled with the radiator fan controller and it looks like it is epoxy-potted (hard to repair). But, just like the blower controller, it needs a good heat sink, as was mentioned here, and it doesn't have fins like the blower controller, but relies on heat conduction to the bumper. Always install tightly with thermal grease, and sand away any rust. My guess is they use "pulse width modulation" to control the motor speed. That switches the current on & off fast (~30 kHz) and the motor averages that. It is the simplest way today to realize variable speed in a DC motor.

 

My experience is that transistors fail open.

Also, a transistor is a solid state replacement for the vac tube, not the resistor. It is actually a switch and amplifier.

As far as I know resistors are still pretty much the same as they always were, maybe smaller in some applications.

 

I have a similar problem in that the cooling fans seem to come on too early at times. I found an engine coolant temperature sensor at advance auto. BWD part # WT5066. Also found the engine coolant temperature sending unit wiring harness...this seems like the wiring you were referring to. However, the sending unit only has a 2 prong connector. Which is the case? 2002 grand caravan 3.3L