Radiator Cooling Fans Run Constantly

The setup is as follows from the above diagram.
Relay 3 energized = both fans half speed.
Relay 1 energized = rad fan full speed
Relay 3&2 energized = AC fan only full speed
Relay 3&1 energized = both fans full speed

So if both fans are running, and the wiring is correct relay 3 is stuck or energized. Or 3&1 are energized. If pulling those relays does not stop the fans they have been wired to an ignition feed.

John (Britprius)

The diagrams I have are somewhat more detailed with added complexity.


John (Britprius)

 

Knew someone could decipher the elec diagram better than I can.

MiniVCI is beyond invaluable. People w/ Macs have used it w/o problem on this Forum. There is some Windows emulation mode or software you would have to get though. If you have immediate friends or friend-of-a-friend in IT, they probably have obsolete XP based laptop(s) laying around, and could donate one to you. Or you could buy an XP laptop on Craigslist for <$75 (probably $50 would be an acceptable price for seller).

 

Like I already said in this topic only problem with Fan relay 3, coolant temp switch, wiring or control units (very unlikely) would cause bough fans to run. And OP (Cory151) did already check that relay.

So basically only wiring and coolant temp switch are left. R134 pressure switch would only run one fan so it’s NOT the problem here.

Coolant temp switch is at the lower right side (passenger side for left hand drive) corner of the radiator. Here http://www.radiator-pros.com/media/catalog/product/cache/3/image/9df78eab33525d08d6e5fb8d27136e95/c/r/cr2758.jpg you can see its place. It’s the lowest on the right side.

If you unplug it and radiators fans stop then that switch is faulty. If fans don’t stop look that wire thought. If you can’t see anything then you need to start measuring that your Prius is wired as it should be.

 

Yes you should try to unplug it and see if fans turn OFF. I don’t know what wire that is it may or may not be the problem.

 

So the switch is the problem. And wiring is ok. You just need to put in new (or used) in there. It’s in inverter cooling loop so filling the system and bleeding it is easy.

Here is the one link to the part Genuine Toyota 04 09 Prius Coolant Temperature Fan Switch 89427 47010 | eBay It’s tightened to 7Nm or 61in-lbs.

Here’s video on inverter coolant change Inverter coolant change: DIY video posted | PriusChat You don’t need to open the drain bolt if you don’t want to since coolant will drain out when you remove that switch. But you will need that video to fill the system.

 

You can easily test the AC part of the wiring. Now by unplugging that switch or later when new switch is installed. Just turn the AC to max and fans should run.

ECU side is bit harder to test since fans turn on at 96c or 205F and higher. It’s hard to get Prius engine that hot and then if it doesn’t work you don’t have temp gauge to tell you it. If you have some device with engine temp display or mini-vci its easier.

But logically there’s only one fault. Probably when you take the old sensor out it has taken a hit in the crash but rebuilder just put it in the new radiator.

 

Yes but actually it’s a switch. It even looks broken and bended in your picture.

Just unplug it. Have bucket under it to collect inverter coolant. Remove it. Put new one in. plug it in. Fill the inverter cooling system with Toyota SLLC and get rid of air like in that video.

 

What does the inverter coolant have to do with the main radiator fans ?........or the "high temp" switch for the inverter coolant either ??

I strongly suspect NOTHING.

 

Sorry I don’t get what you are talking about. That is a switch turns the fans on if inverter coolant gets too hot. It is in the radiator in the inverter coolant side. Bottom side of the radiator is for the inverter coolant. So if you remove it inverter coolant will get out from its hole.

Fans can also be turned on by the AC or by ECU. But in this case it is faulty inverter coolant temp switch that keeps the fans running all the time.

 

OK I don't KNOW this but I strongly suspect that there is another sensor on the main coolant loop somewhere too.........and that the system will not sense an engine overheat by virtue of the inverter coolant loop. The ECU should have it's own sensor to detect cold start and overheat and that could cause the fans to run continuously too.

The inverter could be HOT when the engine is not and vice-versa.

 

Of course engine has its own temp sensor. But it doesn’t matter here since it’s the faulty inverter coolant temp switch that is turning the fans on all the time.

 

I am truly sorry for MY confusion.
It was not clear, at least to me, from the previous posts which sensor/switch was being dealt with.

 

Likely not. It will know if the sensor is not connected at all but has no way to tell if it is giving out an incorrect reading.