Toyota Sienna Forum - banner
1 - 4 of 4 Posts

· Registered
1 Posts
Discussion Starter · #1 ·
Yes even when the engine is cool no the air conditioner is not on defrost or Is on position. The temperature switch at the bottom of the radiator reads all zero out when cold Using my multi meter to measure ohms. and if I unplug it fans stay on but shift to low speed. The temperature sending unit next to the thermostat I have replaced As a good measure effort just because of how nasty it all was Is when I replaced the thermostat. the temperature sending unit itself I get no change fans when I unplugged it. I also jumped The thermal sending unit next to the thermostat And the fans did not go to regular function. I did jump the AC high pressure switch switch which also had no effect on the fans. I played Musical chairs and rotated all the relays which also had no effect. A little bit of back history about this man and when I 1st 1st bought it it worked fine and came on it the appropriate temperature and then turned off when no longer needed. I did a timing belt, water pump, plugs, coils, Thermostat coolant temperature sender next to the thermostat and brand new radiator. The Van was in limp mode when I started It had a serious loss of power. However now it's at full power runs good. Been doing most all of this off of reading the forums and a whole lot of can do attitude and sometimes a little set electric is my weakness. I'd rather replace a whole engine rather to mess with an electric wiring harness! Anyone so if you could please advise thank you very much

· Premium Member
2014 Sienna LE
867 Posts
If you have an OBD reader, as mentioned above, checking coolant temps would be good. If the van thinks the temp is really high, then it's going to run the fans constantly.

I also jumped The thermal sending unit next to the thermostat And the fans did not go to regular function.
I'm not sure jumpering it will cause the fans to turn off.. This is a typical variable resistance temp sensor, not a switch. The resistance lowers as the temp heats up, so shorting the connector is going to indicate a very hot engine.
Parallel Font Slope Rectangle Drawing

Reading some other stuff, if the temp sensor is disconnected, the fans will turn on. This is counter to the lower resistance = hotter temp at first glance, but it's likely a failsafe. If the resistance is too high, they assume the temp sensor is either bad or disconnected, so they turn the fans on to be safe.

I'd check the resistance of the temp sensor, though again, an OBD reader will be best. Knowing what the car thinks is happening is best. I'd plug in an OBD reader and look at the coolant temp. If it's unusual, try unplugging the temp sensor. If the temp on the OBD reader doesn't change, you probably have a short or open circuit somewhere in the wiring harness, or a bad ECU (unlikely).

If the temp on the OBD reader is normal, then something in the control circuit is messed up.
1 - 4 of 4 Posts