My parents own a 2009 Camry V6 XLE with about 60k miles. For the past few months nearly every time it rains or is very wet outside BOTH radiator fans will turn on by themselves until they drain the battery. If you turn acc or the car on the fans will turn off unless you make them turn on with the a/c or defrost.

I pulled the relays and tested them to make sure they switch and for continuity and they checked out. Coolant level is fine and the temp sensor appears to be working since it shows temperature on the dash. I searched all around and only found one other person with a Rav4 that has the exact symptoms but they took it to a dealer and they "fixed" it with no reported problems.

Any leads on what could be causing this or what could be getting wet/shorting/grounded that would cause the fans to turn on? Also does anyone have the fuse block diagram for under the hood? The lid of the fusebox appears to be the for the 4cyl and not the 6.

 

The actual fan on/off operation is controlled by a cooling fan ECU (location on drivers side of center of radiator).

Fan power runs from the battery through the FAN MAIN relay (location in relay box on drivers side engine compartment) to the FAN ECU. The FAN MAIN relay is on when the Start button is pushed or ign key to on.

The FAN ECU then turns the fans on/off based on inputs for A/C, cooling system, engine operation.

The FAN ECU has 3 wires. White/black is ground. Black is battery power from FAN MAIN relay. Green is the control wire from engine ECU. Not sure what type of input signal is on green wire. Toyota tends to have the ECU ground a wire to complete a circuit.

There is short pin in the green wire (removable link in wire) under the dash, passengers side behind glove box.

Unless power is back feeding via green wire and some kind of internal issue in FAN ECU. The FAN MAIN relay would need to be closed (powered) to allow power to the FAN ECU.

Check if FAN MAIN relay or socket has issues.

Could get use a sprayer to mist the engine compartment areas with water to try to simulate rain.

 

Thank you VERY much for the logic behind how these fans operate. I will inspect these wires and fuse block again for any signs of water ingress. I did try spraying various spots with a hose while the car was off but couldn't get the issue to replicate. I then turned the car ON with defrost on then the fans came on. I then turned the car OFF and the fans shut off for a second then came back on full blast with everything else off.

Do you happen to have access to a engine fuse block diagram? The underside of my cover does not match my fuse/relay layout and appears to be from a 4cyl instead of the 6cyl that the Camry has. I tested most of the relays underhood but want to be sure I am testing the correct relay/socket. Thanks again!!!!

 

The owners manual has the fuse arrangement. If no manual find it at the link below:

https://www.toyota.com/owners/resources/owners-manuals

 

My owners manual has the Fuse only layout. It does not show the relay layout. Searched online and youtube and found plenty of the 4cyl but none of the 6cyl.

 

Don't have this info.

Its one of the relays in the picture below:
https://parts.villagetoyota.com/a/62...6420-8401.html

A 4 prong relay socket.

For a small fee can access toyota data at the site below for 2 days:

https://techinfo.toyota.com/techInfo....toyota.com%2F

 

I wanted to follow up with a resolution since it always annoys me when other people don't.

All relays and fuses checked out fine and nothing looked out of place. I sprayed the car down and watched where water traveled. Some went down on the driver side of the inner fender and ended up around the main fuse box. I removed the fuse box and the little side panel on it held down with a few screws. Behind that there are a few connectors and one of them looked to have had some sort of dielectric grease applied to wires going in and the connector portion of it. I cleaned it then reapplied new grease.

Reinstalled the fuse box then added some RTV/silicone where the windshield cowl meets the rubber fender gasket to divert the water away to the outside of the fender. I added a couple washers behind the fuse box top screws to offset it from the fender some. Also re positioned the plastic fender cover near the fuse box to give it more room.

It's been through a few storms and have driven it in the rain without the fans coming on so I consider it problem solved.

 

Great job in fixing the problem!

Thanks for posting back with your fix!