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Ask Kurt Kennedy Your Own Question
Kurt Kennedy
Kurt Kennedy,
Category: Toyota
Satisfied Customers: 93
Experience:  Shop foreman at Auto-Lab of Texas
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Fan turn on when car turns on. JA: Sometimes things that you

Customer Question

fan turn on when car turns on.
JA: Sometimes things that you think will be really complicated end up being easy to fix with Toyota. The Toyota Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so he can help you best.
Customer: I have already done a ton of things, and know my stuff. The fan turns on as soon as I turn on the car, even to the first position without starting the car. Even with AC off and all fans off. Main fans still turn on.
JA: Many things can cause trouble with the A/C. Some simple, some complicated. Fortunately, the mechanic I'm going to connect you with knows all the tricks and shortcuts. Are you hoping to fix this yourself?
Customer: Yes
JA: Great! What have you tried so far?
Customer: That is a really long list....but here it goes: Direct connect to fans, to make sure both fans work (yes). Replace main fan computer, same issues. replace relays that run fan, or any fan related system, including switching similar relays around, same issue. Check all the fuses under the hood, and in the cabin, all fine. Replace main ECU and flash ECU to sync. Car runs fine, fan still runs all the time. Ohm out all the wires between fan ECU and main ECU and fues box, all fine. Replace car temp sensor, same issues. Check AC with guages, correct per specs. Run TIS diagnostics, no errors.
JA: Is there anything else the Toyota Mechanic should be aware of about your Toyota?
Customer: that is just the start...
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Toyota Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Toyota
Customer: replied 1 year ago.
side note....I started this once before with I have done several other small things like checking connectings. One other issues that seems related....the AC light blinks inside on the AC button. The AC can get cold if I wire past the relay. Is there anything in the condenser that caues the fans to act funny? The fan can even turn on when the car has been parked for hours....and just kick on for a few minutes. Middle of the night, hours after the car has been turned off, the fans can start and run for like 30 seconds with a cold car.
Expert:  Kurt Kennedy replied 1 year ago.

Just so we are all on the same page can I please have the year, make and model of Toyota you are working on please?

Thank you!

Customer: replied 1 year ago.
2008 Toyota Sienna LE
Expert:  Kurt Kennedy replied 1 year ago.

1. Since you said the check engine light does not come on, check the EFI fuses and the EFI main relay operation.

2. If the fuses are good and the EFI relay is being energized, check to see if the 5 volt reference is shorted going to the throttle position sensor, accelerator position sensor and the evaporative system canister assembly.
3. Check the power and grounds at the engine control module.

You said you have replaced the cooling fan module, what about the ECU, with a new one from Toyota?

Thanks!

Customer: replied 1 year ago.
Correct, no check engine light. Car runs fine, just fan runs 100% of the time. Yes I have replaced main ECU, with 2 different ones from junk yards, both with exact part numbers, I know they are not the issue. Between mine, and the 2 others, I have tested 3 of them. Odds its the ECU is next to none, and since new ECU from Toyota is almost $1,000 bucks thats the best I can try on my own. The car runs fine, we use it every day, not sure what the EFI (Electronic Fuel Injection correct?) would have to do with the fan running all the time. Power and grounds at ECU are all fine. Ohmed them from the fan, all the way back to the ECU. I have also tested all the fuese behind the glove box, and they are all fine. Can you hlep me me understand what the Throttle position sensor has to do with the fan...accelerator position sensor or canister. Should they be getting 5v when the car is running? How am I testing those?
Expert:  Kurt Kennedy replied 1 year ago.

After looking at the wiring diagram, the 5 volt ref. is a signal shared by multiple components and if one of those is creating an issue, it can do funny things to the rest of the circuit.

If you have a volt meter, you can check them that way, or just unplug them one at a time while the fans are running with the car off and see if the fans stop running after one of thoes items is unplugged. I know it seems odd, but trust me, there is a method to the madness.

let me know what happens!

Customer: replied 1 year ago.
TPS disconnected, accelerator sensor disconnected, evap disconneted, fan still runs with key at position #1, although I do have to hand it to you those are all things I have not tried yet....but none of them worked. Whats next?
Customer: replied 1 year ago.
a few other updates if they help, I actually have 3 fan computers....ebay (the fans started having issues last summer). The original one causes both fans to work when plugged in, the other two both exact same part, cause just the passenger side fan to run then the key is in #1 position. With one of the non original fan ecu (still oem) when I use alligator clips to just bridge the main positive and negative wires, the passenger fans still runs, meaning the red/yellow signal wire is not doing anything to the Fan ECUs, from what I can tell. Even when I bridge the gaps manually (trying to make sure the contacts are happening in the plug) still nothing different, fan still runs. Voltage tested the signal wire, and no 5 volts when the fan was running, so I omed out the wire back to the main ECU and it was still good connection, but no voltage. This is where I have tried the other two Main ECU computers (each needing a flash reset each time) and neither one seems to send signal. What is it that causes the main two wires to default to on, or for the relay to be tripped, if there is no signal wire 5volts? Crazy thing is that it can be turned off for hours, cold.....and just randomly it will turn on the fan. What signals to turn on the fan, when there is no power to the fan ECU and no key and the car is cold, and its not the relay, I have 3 of those also and have tested them all, along with any other matching relay. No change no matter what relays I use. Lost.....I have worked on cars regularly for 15+ years and this one is something I just cant seem to solve....thanks. Look forward to more ideas.
Expert:  Kurt Kennedy replied 1 year ago.

I agree, this is tricky one. Thats why I took the question, I like odd ball issues like this. Give me some time today, to look over the wiring diagram and send you a copy of it, and we can walk through it, step by step and find this issue if that works for you.

Thanks!

Customer: replied 1 year ago.
By the way I have the full official Toyota service manual, and full wiring diagrams but fell free to send me your version if you want to walk through it together step by step. I even have the Toyota service program TIS on a laptop. T
Expert:  Kurt Kennedy replied 1 year ago.

SO what I am going to do, is have us start at the start of all this ,and unplug items one by one untill we can get the fans to turn off (with the key being in the on position)

bear with me a little as we walk through this some of it may seem like things you have tried, but I want to start from scratch, and get this figured out.

The first thing I want you to do, is turn the key to the on position so the fans will turn on. Then remove the IG1 relay, and let me know if that kills the fans or not.

Expert:  Kurt Kennedy replied 1 year ago.

Here is the diagram I am going off of.

Expert:  Kurt Kennedy replied 1 year ago.

Also, have you checked coolant temp. data with a scan tool to see what the temp. is reading from the sensor its self? If not, try that also just to make sure we dont have something there

Customer: replied 1 year ago.
Ok, coolant temp sensor replaced 3 days ago , attempt to fix this also. Temp sensor reads and works fine, in dash gauges, and on obd sensor read normal. When hot OBD reads 78C on bluetooth obd scanner. Not quite sure where the IG1 relay is but I think its drive side kick plate. Pulled all 4 relays there, one at a time, until they were all out, and car starts, and fan runs with all 4 out. I only figured out where they were from the T-SB-0047-09. So from what i can tell, removing IG1 relay, provided it was one of those 4 down there, did not turn off the fan. Pulled both the pink ones, and neither one stopped the car from running. My manual does not seem to show where the IG1 relay is.....
Customer: replied 1 year ago.
sorry just confirmed, the pink one on the lower kick panel, on the far right side, is the IG1. Yes I pulled it, Yes the car still starts, yes the fan still runs.
Customer: replied 1 year ago.
One other note, pulling the EFI relay, stops the fan, but the car does not start. and switching the EFI relay with another ones the same....does not fix the issue. Car still starts, but fan still runs.
Customer: replied 1 year ago.
A few more notes: Looking at the diagrams I wanted to then see if I pull IG1 AND the 10A HTR fues if the fans would run, yes they are running with both pulled. So somehow the fan relay is getting power to close the gap on the relay and power the fan ECU. The only contact it could be would be the #3 and #5 contact on Fan Relay, spontaneously connecting, since its not happening from the #1 and #2 sides with the 10A HTR and IG1 relay pulled. And this would make sense by it can happen, on a cold car, with no key. Still points back to the fan relay right....but I seriously have 3 of them, one which is new aftermarket, and all 3 exhibits the same behavior AND its the same relay as about 5 others in that box, and NONE of them work to fix the fan issue. I can go and try and buy another one directly from the dealer tomorrow, but being that its a common relay, I have switched it with almost every other one under the hood that is the same blue color/part number, I am not confident it will make any difference and its like $50 bucks. Idea....Does the fan always run for the first X number of seconds, just to test the fan function? If so what is the function that tell its that it is indeed working and to turn them back off? I know the fan NEVER turns off even if its cool, or idling, its always on, not just the first little bit but my other car does have that function to "test" the fans. I wonder if there is something that is not telling it the fans that they are working and not to turn them back off after X seconds..just and idea. I dont even know if Toyota do this or not.
Expert:  Kurt Kennedy replied 1 year ago.
I don't think it's a relay issue. There is nothing special about that relay.If you pulled the EFI fuse. And they stop, you have an issue with the fuse box the relay sits in I am thinking
I had a land cruiser a few years ago, the DVR and Nav stayed on constantly and would kill the battery. Turned out the fuse panel that held the fuses got a little burnt and shorted the circuits together and kept everything powered up.Let me look at a diagram shortly and get back to you. I think we are on the right path.
Thanks for all your info
Expert:  Kurt Kennedy replied 1 year ago.

Alright man. I ve done some digging this morning.

I think I have isolated your issue down to the junction block inside the engine bay. I am going to be sending over some documents.

With the EFI no 1 fuse pulled, you said the fans turned off.
The EFI Relay is in the engine bay junction block. With the EFI fuse in, pull the relay, what happens?

Pull the 30a RAD NO.3 fuse, after it is all back together and fans are still going. what happens (same junction block

Pull the Short pin out of the juntion block, same condtion, fan running key on. What happens?

I think its going to be the connector on the back side of the fuse block that I am attaching with this info.

In the diagram I attached with the connection highlighted in red and an arrow pointing to it, that is the junction block under the hood So if the HTR fuse is removed, yet the fans stay on, the next step in line is the junction block. If you pull the EFI NO.1 fuse in that junction block and the fans stop, we have it isolated to this junction block.

I really hope this makes sense and PLEASE feel free to ask any questions regarding my testing.

Customer: replied 1 year ago.
Thanks for all the feedback so far. I should be able to test these suggestions tomorrow.
Expert:  Kurt Kennedy replied 1 year ago.

Awesome! Did you have any questions about what I am suggesting to try? Are you able to follow my thinking on why I am suspecting the junction box?

Customer: replied 1 year ago.
I am following it, I too seem to think its maybe in the junction box, especially since I have pretty much replaced everything else in the system. I will report back likely tomorrow with whatever I find.
Expert:  Kurt Kennedy replied 1 year ago.

Awesome! let me know!

Customer: replied 1 year ago.
All these assume it the only thing removed from an otherwise functional car:EFI relay pulled= no fans, no start
EFT Fues #1 pulled = no fans, no start
30A RAD#3 pulled = yes fans, yes starts
Short Pin pulled = Yes fans, yes starts.I am going to start to dig into the back of the junction box to see what I can find (corrosion/connections ect) but wanted to give you an update to see if this gives you any more info to pint me in the direction to locate the issue.
Customer: replied 1 year ago.
Sorry eft fuse #1 should have said efi. Pulled every other fuse and relay in that box one at a time and the only thing that shuts off the fan is the main fan relay and those efi fuse and relay. Even pulling the fan fuses don't shut off the fans... Digging in...
Expert:  Kurt Kennedy replied 1 year ago.
It has to be a sticking relay ( did you try to swap the main fan relay with another? )Or the connections under the fuse box. Like you said, either corrosion or burnt connector, Etc
Customer: replied 1 year ago.
pulled the junction box apart, even pulled all the fuses, and took the internals of the top half of the junction box (part with EFI relay and all the fuses) apart, until I could see the board/connections inside from one side to another. Looked at every connection, cleaned them all up with electronics cleaner, put them all back together. They all looked normal and fine. Did not appear that anyone had ever been in there since the factory install. Cleaned every connection with electronics cleaner, put it all back together...same result, fan turns on when key in position #1. I have switched almost every relay out with other ones that are the same, including the fan relay, IG1 relays, EFI relays, I have double checked every fuse, and every relay. Switching out and replacing the main fan relay was one of my first things I did when I started this, as its a common problems that people say happens. I have a new one, and it still doing it. I have switched it with several others, all the same, and fans still turn on with key. I am chasing down the power source. On connection 11092 the red/yellow wire also has a black/white wire in the same connection, everything looks stock, perfectly crimped. What does the black/white wire go to or from? I have pulled the 10A HTR fuse in the driver side panel, and so I know the yellow/red wire should have no power going to it in 2c2. Poking around I have figured out when I pull 11853 connection(all which have power with the key on) that fan turns back off so somehow power is coming from one of the wires on 11852 and going to 11092 on the 2f3 position likely via the black/white wire...I am going to start to see if I can disconnect the black white wire to isolate the power source, and/or remove the wires one by one in the 11852 connector to see what is feeding it power. Any other ideas? Just an update where I am at.
Expert:  Kurt Kennedy replied 1 year ago.

There has to be an issue with connector 2F or 2C in the junction box. Like we talked about before. Take the junction block apart and check thoes connectors that come underneath the junction box and check them for burning, chaffing, or corrrosion.

Expert:  Kurt Kennedy replied 1 year ago.

Sorry, I did not see your post at 9:58 when I wrote that. Disregard. let me check on your info.

Expert:  Kurt Kennedy replied 1 year ago.

The only thing that connects connectors 11852 and 11092 is the circuitry in the circuit board of the junction block.

I think you have a bad junction block buddy.

The black and white wires should all be Ground.

Expert:  Kurt Kennedy replied 1 year ago.

EFI fuse has NOTHING to do with the cooling fans. the only thing that connects that to the cooling fan system is the junction block.

Customer: replied 1 year ago.
I can try and replace the junction board but the connections from one side of the junction box to the other, are all pretty straight forward. Don't know if you have seen the inside of one, I never had, but the connections are big fat metal connections from one side to another. Its not like a computer circuit board, with lots of little wires that are hard to trace, its large metal connections from on side to another separated by obvious gaps and spaces you can visually see the connections from one side to another, and they are obvious. Do you happen to have any wiring diagrams on the internals of the junction box anywhere. Where I could ohm it out from one side to another and see if there is anything wrong. I may just manually chance it from the sources on 11852 and see where it connects from.
Expert:  Kurt Kennedy replied 1 year ago.

I just tried finding how the circuits run in the EWD, and no luck :(

Customer: replied 1 year ago.
the black/white is grounded....so I removed the 3 layers of the junction box, removed all the connectors, and make sure it was all clean, and put it back together. There was one connection that was questionable, so I cleaned it up, and omed it out to make sure it was good, but it went to the 10A dome fuse so seems pretty unrelated. Just for reference sake, here is the inside of a junction box. You will see its pretty straight forward, cleanable, and serviceable but I am sure nobody else would bother taking it apart. Everything looked like it should, clean, connected, no corrosion. I put it all back together, and tested. The car runs fine, the fan still turn on in position number 1 and pulling the EFI relay, kills the fans. I can try and find a new junction box but I am pretty concerned it will not fix the issue after I have seen the inside and it all looks like it should.
Expert:  Kurt Kennedy replied 1 year ago.
Thank you for the pictures. Just to humor me, with the fans on, unplug the pressure sensor on the AC line and let me know what Happens.I'll do some more digging into wire diagrams tomorrow.
Thanks!
Customer: replied 1 year ago.
Key in position 1 fans running, pulled ac pressure sensor and fans keep running car startable.
Customer: replied 1 year ago.
A few more pieces of information.one by one pulled the wires from 11852, to see which ones kill the fan. All of them had nothing that impacted the fan in any way, except for #1 (Red/White) which did ohmed to negative, and the #6 (black/White/gray spots) which did not ohm to negative, but had almost no power (0.07). I dont know if that helps. But I was hoping it might....Thanks for your patience so far trying to get to the bottom of this one, not sure how I put more money in the juke box but we have defiantly gone more than one song on this one. Is there a way I can paypal you more money at the end if/when we solve this?
Customer: replied 1 year ago.
a few more pieces of information: I did some more testing....when I jump from 3 to 5 on the EFI relay, the fans turn on (EVEN without the key in the car,first time this has happened in testing). When I jump only from 1 to 2 on the EFI relay, it does not turn on at all. When I pull the EFI No1 fuse and then jump from 5 to 3 fans to not turn on. So whatever is causing the power to get supplied to the 20A EFI No 1 fuse, is sensitive enough that sometimes it trips on its own with a cold car without the key, and it always trips when the key is on. Because its temperamental, I seem to think its a relay not a fuse or fusible link, just somewhere further up the line that supply's power to EFI fues No 1. Now I have seen the power diagrams, and Fans dont seem related to EFIs at all, I know, but I am going to assume we are just missing something further up the chain, that is related. None of the other fuses in the engine room fuse box will make the fans turn off so. I know that wire 1 2H will kill the fans and is grounded, and 6 2H kills the fans and has LOW voltage. I have tried other relays in the EFI relay, but am tempted to just go buy one or look one up to make sure it was not somehow mixed up in the process. There are several different 4 pronged relays, I need to find a way to double check the right part, just in case it was ever switched, or replace Wong. With the EFI relay in, if I pull the Defog relay, fans still run. If i pull the 10A EFI No 2 fans still run. So the power source has to be up stream from 6 2H becasue I know that 1 2H is a ground. I know that 6 2H which only has the MREL next the the name of the computer. I think I found that MREL is the main relay. Where is the "main relay". Where is the 30A AM2 relay? is there anything upstream on 6 2H (besides the computer, I have tried 3 of those). Hopefully this is helpful.
Customer: replied 1 year ago.
Correction: 1 2H is hot, even without the key. 12v. That means that 6 2h is supplying the voltage to trip the EFI relay. I dont know why the EFI is related, or if it is but I know I can trip the fans by wiring past 5 and 3 on EFI.....and that 6 2H seems to be supplying the current to trip the relay and the voltage comes from either 1 2D or 1 2H. that is all for tonight. I need to go to bed.
Customer: replied 1 year ago.
Do you still feel fairly confident its the junction box, even after seeing the photos from inside the junction box? I can buy a new/used one but I am just concerned its not the issue after I cleaned it all up, checked every connection and put it all back together and it still had the same issues. Any other ideas based on the information I supplied? Are there any other replays or things you think I should check that are not in the main relay box under the hood?
Customer: replied 1 year ago.
Any other pieces of information or feedback? I have not heard from you in several days.
Expert:  Kurt Kennedy replied 1 year ago.

I am sorry. I have been very busy. Ill dig into what you posted on the 6th, and get back with you tonight. Sorry about that!

Customer: replied 1 year ago.
No problem I dont have time tonight to deal with it directly, I just was not sure if you were willing to still offer any feedback. I can wait a day or two if that works better for you, I just wanted to make sure you were still willing to work with me. Thanks man.
Customer: replied 1 year ago.
Never heard back from you.....any updates?
Expert:  Kurt Kennedy replied 1 year ago.

Sorry, your post got lost and never showed up on my screen of questions and I had no idea how to get it back!

Did you ever find anything out or do any more testing?

Customer: replied 1 year ago.
Nope, everything I have figured out is in the notes...I am really at the end of my stick for options....I cant think of another thing that would cause the issue. One night when the car was cold, and the fan had kicked on (with the key off and a cold car) I went around and tapped on all the relays under the hood, and under the drivers side kick board on the main fuse box....taping on them each resulted in nothing different.....the fan still ran....then when it wanted about 30-50 seconds later it turned off....tried tapping on the fan control module, ever relay under the hood, and all the ones on the main box inside....I am telling you its crazy. that junction box is clean and no reason to believe it has any issues, and looks perfectly normal....I really dont know man. How would the fan get power, with the key off and a cold car, randomly. I am still thinking relays or some sensor since its random but I just dont know. I have tried switching relays around, have several new ones and still, nothing makes sense.