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Rad fans don't come on when they should - getting weird volt readings at the connectors

This is kind of continued from another thread but the other thread was more for a different problem (what would I do without car problems!) so I’m starting a new one.

Vehicle is a 2001 Grand Caravan, 3.3L V6, 100k miles.

The fans stopped running a couple weeks ago, I noticed the engine temp was higher than usual (not quite half way, but higher than the one notch below half it usually stays at). Popped the hood and noticed the fans were not running. Tried turning on the AC, still no fans. Once I got back on the road and out of traffic, the airflow cooled things back down and it’s been mostly fine since, never gets over halfway.

I checked the fuse, it looked good, tested it with my multimeter, and tried a known good fuse just in case, didn’t help. I’m suspecting the rad fan relay since both fans don’t run and I doubt both motors failed at the same time?

Today, I tried pulling the connectors to the fan motors and hooking up my multimeter to them. Both gave readings of 8.4 volts with the van off(!), and 8.6 with the van on. Seems odd to me. I tried getting the van hot and checking them again, same voltages. The fans don’t run with this voltage applied (i.e. plugging the connectors back in), and I checked the battery and I’m getting 12.8 volts with the van off and about 13.9 with it on.

Any ideas? Is this normal? Could a bad relay be showing these readings, and should there be any voltage at all with the van off? I know the fans used to run.

Appreciate any help tracing this down (even from crankwalk! haha :).


The fans arent siezed are they?(I had to ask) As a diagnostic technique Try powering the fans up direct. Provide battery voltage (with a fuse of appropriate amperage rating inline) and provide the fan a ground. (I would put a ampmeter in series,meaning open your improvised circut one side into your amp meter the output from your meter completing the circut. Make sure your meter is set to Amps wires plugged into meter for amp setting,make sure meter is set to an appropriate range (dont want to blow a fuse in the meter,sometimes thet are hard to find) with this test circut set up the fans should run watch amp meter for a high amp draw (I dont think the fans should draw over 15amps but I am not exactly sure but close. What Iam thinking is your fans are drawing too much amperage hence the low voltage reading (your voltage reading is with the connector hooked up isnt it?) you could test the voltage with the connector disconnected from the fan motor (you should see battery voltage) you will need to have the AC switch on I believe there is always voltage at the fans with AC on no matter what the engine temp. Keep hands clear of fan blades(I know this is obvious but you must be careful when "hot wiring yor fans this is what I am sugesting to verify fans run and amperage draw is within specs. Did you verify the fuse in the box for the fans is of the correct amperage rating? this is important for safety. The question is what is pulling the voltage down this low first verify they will runn with battery voltage applied. Be safe

You will have power to the fans, the PCM grounds the circuit to allow the fans to run. Try applying power to the fan motor and grounding the other terminal, see if they run.

Going by the voltages you read it looks like there may be a faulty power connection to the fan relays or the relay is bad. The info I looked at shows that fuse #27 supplies power to the relay via a orn/red wire. Make sure there is 12 volts on the wire, at the relay. If that is ok then see if the dk blu/dk grn wire going to the fans has 12 volts on it. The relay may be the source of trouble here.

Thanks oldschool. I think that amp meter testing is a little behind my skill level but I appreciate you laying that out. I’ll see if someone can help me with that.

My voltage reading is actually directly from the connector contacts, unplugged from the fans. And the fuse in the box is 40A, which is what it should be…thanks for the tips!

Thanks Cougar, willey. I tried applying power to the fan motors but the connectors are very hard to get at, and you have to try to hit the right contact blindly. Haven’t gotten it to work that way, but I’m sure both fans didn’t die at the same time. I’m going to try replacing the fan relay and see what that changes, if anything, and then go from there.

I did some research and the voltage readings are normal. The voltage starts at 30% (30% of 12 volts is 8.4)and goes up as the engine temp increases. It is a variable speed system.

THANKS! So, what does that mean? The relay isn’t allowing the full 12v to go when it should? Does that rule out any wiring issues? Like I said, the fuse is definitely good. What about the CTS? I read that there’s only one CTS in this vehicle, so if the dash gauge is showing over-normal-temp, shouldn’t the PCM be getting the same signal?

Also, does that mean it’s normal that I’m getting the 8.4v when the van is completely off? As I indicated before, the fans do not run at all with the 8.4/8.6 volts.

The system has a INTELLIGENT POWER MODULE, the PCM, and a RADIATOR FAN RELAY MODULE. They work together to control the fans and their speeds. The 8.4 volts is normal at low engine temps, the fans work at slower speeds. As the temp increases the voltage increases to allow the fans to run faster.

Here is the description of operation from ALLDATA…

The solid state radiator fan relay is controlled by the Powertrain Control Module (PCM) by way of a Pulse Width Modulated (PWM) signal. The relay control circuit supplies a 12 volt signal to the PCM. The PCM then pulses the ground circuit to achieve fan on time. The relay provides a voltage to the fan motors which is proportional to the pulse width it receives from the PCM. The duty cycle ranges from 30% for low speed operation, then ramps-up to 100% for high speed operation. This fan control system provides infinitely variable fan speeds, allowing for improved fan noise, A/C performance, better engine cooling, and additional vehicle power.

Thanks again willey. I just hooked up direct 12v power to the fan motors, and both fans ran without a fuss.

I’m starting to really suspect the fan relay, what do you think based on all the factors?

I would suspect the ground circuit. If you have power to the fans then the relay and PCM are working fine. Unplug the fan motor connector, use a 12 volt test light hooked to battery power. Probe the connector terminal (harness side/not motor side)that has the black wire with a dark green tracer. The test light should light indicating continuity to ground.

If the light doesn’t light check the ground connection. It’s located by the left front headlight.

I am getting voltage (to a multimeter,not test light) at the connector terminal, harness side. But the 8.4 or 8.6 volts are not turning the fans when plugged in to the motors, and I’ve not seen the voltage go above 8.4/8.6. Plugging test wires from the battery to the motors, giving them 12 volts did run the fans, but they aren’t running at all plugged into the proper wiring.

So that’s why I think the ground should be fine, but perhaps the relay is not operating properly. Does that make sense, or did I misunderstand what you wrote?

You have power to the fans so you need to find out if the ground circuit is OK. Having a 12 volt test light connected to B+ will check for continuity to ground on the black wire with a dark green tracer.

I don’t have a 12 volt test light, so I’ll have to see if I can buy/borrow one.

Here’s a new development…I had my laptop hooked up to the van today after a drive, and the temp started to climb and got closer to halfway, and the software was showing the temp close to 200F…well when it hit 200, I heard a fan come on! I popped the hood and sure enough, the pass side fan was running. The other one is not hooked up right now.

Before, neither was coming on, but I never let it get to halfway. And before all this, the temp never used to climb towards halfway, the fan(s) kept it at a notch below, with no movement. So I’m wondering if a bad relay could not be allowing the low speed/lower temp fan to come on, but the high speed/higher temp fan is still functioning? Or could a ground circuit still be at fault.

This is fairly normal. One fan is controlled by temperature and the other by computer. However, I would check the temperature sensor for the fan that kicked in. Or simply replace, they are usually fairly cheap.

Teh fans on the GC are switched on and off by a Solid State Relay, which is located down on the chassis rail under the air filter.
It offers variable speed by means of a Pulse Width Modulated signal from the ECU. Essentially it is switchign the fan ON and OFF very rapidly for varying periods of time. somewhat like a light dimmer on your house electrics.

This relay is prone to failure, it may fail full on or full off. Particularly if somethign obstructs the fan rotation. eg a loose cowling and somethign obstructing the fan blades.
so check the fan for signs of impact with the rad cowling. It may deflect at highway speed and not in your driveway.

However, check the fans with a connection directly to battery voltage first.

Replacing it is easy, It costs about $50

insure to clean any rust and debris off the chassis rail where the relay contacts and also add some heatsink thermal grease, (available from Radio Shack for heatsinks.) It needs the chassis metal as a heatsink, so make sure it is properly attached and contacting.

I cannot remember is there is a Thermal fuse or regular fuse in the circuit, however, I believe the fan is provided with 12Vdc, just like the Ignition coil and the ground return is switched.