what triggers the electric fans?

[walkenvol]

The driver's side electric fan is not coming on when the engine heats up. Its fine driving down the road but the temp starts to rise when not moving in traffic. Turn on the A/C and both the driver's side and passenger's side fans turn on. I took the relay out for the #1 fan and jumpered across which makes the fan turn on. I checked for new voltage at the relay when the engine heated up but never found any. Obviously both fans are functioning but the temperature trigger that turns on fan #1 is not sending voltage to the relay at the appropriate time. The temp guage on the dash is working properly and I found its 2 sensor to be right next to the radiator cap. Where is the sensor that triggers the relay for fan #1 and how does it work?

By the way, this is for a 98 Sienna with the 3.0 v-6. I'm on the camry forum as its difficult to get responses on the sienna forum.

Thanks in advance.

[JohnGD]

I thought the condenser fan only comes on when AC is on. When AC is on both turn at low speed. Both fans will go into high speed mode if needed when AC is on. Otherwise only the radiator fan runs. No?

Originally Posted by walkenvol

The driver's side electric fan is not coming on
when the engine heats up. Its fine driving down the road but the temp starts to rise when not moving in traffic. Turn on the A/C and both the driver's side and passenger's side fans turn on. I took the relay out for the #1 fan and jumpered across which makes the fan turn on. I checked for new voltage at the relay when the engine heated up but never found any. Obviously both fans are functioning but the temperature trigger that turns on fan #1 is not sending voltage to the relay at the appropriate time. The temp guage on the dash is working properly and I found its 2 sensor to be right next to the radiator cap. Where is the sensor that triggers the relay for fan #1 and how does it work?

By the way, this is for a 98 Sienna with the 3.0 v-6. I'm on the camry forum as its difficult to get responses on the sienna forum.

Thanks in advance.

[walkenvol]

I understand the condeser fan to be labeled as fan #2 in the relay cover and is the passenger side fan and yes I think it only comes on when the a/c is turned on. It may also be designed to come on at a higher temp without the a/c but I've not been able to simulate that situation. If I knew where to find a wiring diagram maybe it would show what signals the relays to activate the fans. Whatever is supposed to send the activation signal to the relay that doesn't involve the a/c is not working.

[chronoti]

there is 2 coolant sensors, one for the gauge and one for the fans, there is one where the bottom hose from the radiator connects to the block and one near the fill neck, i believe it the sensor near the bottom hose (next to the trans) that controls the fan, but not sure 100%

[walkenvol]

I noticed what appeared to be 2 sensors on the top near the fill neck. One of them was definately the temp guage on the dash as disconnecting it disabled the dash guage. I didn't observe any change when disconnecting the other one. I'll look down below and see if I can find something there. Thanks for the input!

[sam333]

You have a temperature SENSOR that runs your gauge and temperature SWITCH that controls your fan.

When the engine is cold the ETC switch should be closed( that opens the radiator fan #1 relay) keeping the fan from running. When the coolent is hot, the ECT switch should be open ( closing the #1 relay) and allowing the fan to run.

The second connector you found ,is probably it. Unplug it and test the switch for continuity between the connector pin and ground .If the engine is cold you should have continuity and if hot it should be open.

You can also just unplug the connector and start the the engine and the fan should run weather the engine is hot or cold.

If that does not work, take out the #1 relay and test the pin side for continuity( it is a normally closed relay/ switch) and should show continuity with no power on the coil side.

[walkenvol]

Thanks Sam - I'll test the sensor and relay this evening and report back.

Chronoti - when I disconnected the sensor where the bottom hose from the radiator connects to the block the check engine light came on but no fan came on and I did not get new voltage at the relay. I need to perform the tests outlined by Sam although I'm still not sure which is the correct sensor - the one by the fill neck which doesn't control the dash guage or the one by the bottom radiator hose connection at the block.

[sam333]

If it is just the switch( bad), then as soon as you pull the connector from the switch( coolent hot, ignition on) the radiator fan will run. Look online for manuals for your car to find where the switch is positioned on your engine. If you unplug it and it doesnt run , the next thing to check is your #1 relay.

[walkenvol]

Originally Posted by sam333

If it is just the switch( bad), then as soon as you pull the connector from the switch( coolent hot, ignition on) the radiator fan will run.

I'm a bit confused. If the switch is on and I pull the connector, how will the temp of the coolent be measured?

When the sensor is functioning properly and the coolent reaches the predetermined temp to activate the no. 1 fan, shouldn't there be signal voltage at the no. 1 relay (not the constant voltage being switched by the relay but signal voltage triggering the relay to connect)?

I must not be looking in the right place for the on-line manual?

[sam333]

The switch is just a switch , that opens at around 195 deg f( hot coolent). When it opens the fan runs. So by pulling the connector you have by bypassed the switch and opend it yourself. When the engine is cold( cold coolent) the switch is closed ( grounded) this completes the circuit through the #1 relay coil( the #1 relay is normaly closed )and when the coil is energized it opens the relay, cuting off power to the fan.

Open means passes no current.
Closed means passes current.

I think your are assuming that when the coolent gets hot it closes the switch , completes the circuit , energizes the relay coil , closes the coil points and completes the circuit to the fan and then to ground and the fan runs? At first glance that may look that way ,but that is not the way the circuit works.

Like I said before it is a normaly closed relay and it OPENS ( passes no current) when its coil is energized.

These relays are an electromagnetic switches . There are two parts to the relay( the coil side and the
points side). When you send power through the coil side it either opens or closes the points ,depending on if its a normaly open relay or a normaly closed relay.

[walkenvol]

Sam - thanks for the explaination as its very clear to me now how the sensor switch works. I dropped by my favorite local mechanic this afternoon and used his computer system to view the cooling system diagram to locate the sensor for fan#1. I disconnected the plug from the sensor and the fan didn't come on which leads me to believe its the relay. I don't have my meter with me to test the relay but I think I'll stop by the parts store on the way home and pick one up to quickly determine if that's the problem.

[fenixus]

it may vary between cars, but on my both solaras actually both rad fans turn on when needed based on coolant temperature at fan switch(es).

Originally Posted by JohnGD

I thought the condenser fan only comes on when AC is on. When AC is on both turn at low speed. Both fans will go into high speed mode if needed when AC is on. Otherwise only the radiator fan runs. No?

[walkenvol]

Originally Posted by fenixus

it may vary between cars, but on my both solaras actually both rad fans turn on when needed based on coolant temperature at fan switch(es).

I would suspect that all the 3.0 v-6 toyotas of the same era with dual radiator fans should run the same cooling system. The problem is the system is not as simple as I thought. I wish someone with the knowledge could explain the process but here's what I determined so far.

- the fan on the drivers side is referred to as no. 1 and the passenger side is no. 2
- there is also a fan no. 3 relay and I've yet to fan a 3rd fan????
- whenever you turn on the a/c, both fans turn on regardless of the temp of the engine coolant.
- when the coolant get hot (apx 190 degrees) a sensor on the engine block next to the bottom radiator hose return signals relay no. 1 and fan no. 1 turns on.
- I believe the fans also have a "high" speed if the engine is not cooling sufficiently in the "normal" mode. This may or may not involve both fans but since you probably have the a/c on if its that hot you may not notice.

[fenixus]

correct. I don't remember details, because system varies between 5s-fe and 1mz-fe

although I have never seen fans running at a low speed on either of my solaras. they are either off or on (fast).

I don't know the temperature at fan switch which "activates" it, but the engine coolant sensor for EFI at water pump outlet reaches around 205-214F before rad fans activate (varies between cars and models), that's what I can see through OBD2

1mz-fe uses 2 fan switches (sort of thermostats that open or close control circuit) while 5s-fe uses only 1 fan switch (in bottom of rad).
there is some twist in that, because when you unplug connector from the fan switch in bottom of radiator (on 5s-fe) that is when the fans turn on.

not sure how it works exactly on 1mz-fe. there was a thread about it by Nervous where all was explained eventually for his '96 gen3 V6.

can send you electrical wiring diagrams if you want.

fan no.3 is the cabin blower behind the glove box, unrelated to radiator/ac cooling.

[walkenvol]

Originally Posted by fenixus

can send you electrical wiring diagrams if you want.
.

That would be great as I'd like to understand the system since I've spent so much time trying to understand it.