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Your Toyota Guy
Your Toyota Guy, Certified Toyota Master Diagnostic Technician
Category: Toyota
Satisfied Customers: 591
Experience:  I have been/am a Toyota technician for 15yrs+.
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Toyota Sienna LE: 2008 Toyota Sienna. Symptoms: AC system not

Customer Question

2008 Toyota Sienna. Symptoms: AC system not blowing cold air, AC light blinking on AC Button, Radiator Fans not turning on
Submitted: 1 year ago.
Category: Toyota
Expert:  Your Toyota Guy replied 1 year ago.
The blinking light indicates an electrical failure, the most common cause is the magnetic clutch relay in the under hood fuse box, on the driver's fender. It will be designated on the cover as MG/CL or the like, if you can tell me what color it is I can help further, as certain ones are known to go bad.
Customer: replied 1 year ago.
I am not sure if it added everything I have tried:Troubleshooting so far: I have double checked the 7.5 a fuse by the main car ECU, double checked every fuse under the hood, double checked every fuse under the driver’s side foot panel, all fuses match the book and all tested fine. Used a set of AC gauges and low side pressure is 30, and high side is 80 (normal per book) with AC running but AC clutch was not be engaging so I wired past the clutch relay and forced it to activate and the ac clutch engages (still no cold air). I figured maybe it was the AC relay, so I replaced it with the starter relay (identical) and the starter worked fine, and the AC clutch still did not engage on its own when AC was running, ruled out the compressor clutch and magnetic clutch relay. Noticed that the main radiator fans don't turn on when I have the AC running. I knew at least one should turn on when the AC is running to cool the AC condenser and both should run if I disconnect the temp sensor. So I hotwired and tested the two fans, they both worked great (ruled out bad fans). Ran the car for 20 min at 2000 rpm and I have an OBD tester that gives temp and it got to 100C and the fans never turned, they should turn on at 97C based on the official Toyota service manual, which I have on CD with all wiring diagrams. Main car temp gauge worked fine. Because the radiator fans never turned I started to focus on them, knowing that the car could over heat if they don’t work and figure they were related to the AC not being cold with no air flow past the condensers. Tested voltage going to cooling control unit, 13.2 v in with car running, but still no radiator fans. Ohmed out the negative main power supply to the cooling control unit, it was good. Ohmed out the negative from cooling control unit back to the related relay contact, they were good. Replaced the main fan relay and the heater relay with new ones, just because lots of forum posts on them being a common problem. Ran 12v to several other related relays and ohmed out the contacts that close with voltage, they were all good. Looked at all the contacts under related under the main fuse box, they all looked fine. Disconnected the engine temperature sensor (which should kick on both the fans full speed and throw p0118 engine codes, engine codes thrown, but still no radiator fans). Reset codes. Figured it may be the cooling control unit, replaced it with a used one from ebay, fans still did not run. The cooling fan control unit is activated with RF signals from the main car ECU via a Red/Yellow wire. Toyota service manual says replace cooling control unit first and then main ECU if still not working. Since I don’t have a way to test RF signals from the main ECU I ohmed out the red/yellow wire that runs from the cooling fan control unit back to the main car ECU plug, it ohmed out good. Only thing left from my calculations was the main car ECU. Replaced main car ECU with the same make, model, and year from ebay and did the “handshake” method to flash the main car ECU by shorting the TC and CG on OBD port for 30 min, per Toyota directions for replacing ECU with used one. New (used from ebay) main ECU now runs the car just fine after the flash, but still no radiator fans with engine temp sensors disconnected or up to temp. I have the Toyota TIS system on an old laptop, it throws no codes and everything tests fine related to radiators and fan system.The only thing I can guess is the used cooling fan computer, or used main ECU is bad. Bamboozled and befuddled I am out of ideas. I have no idea what else to check to make the cooling fans run. I have wiring diagrams for everything
Customer: replied 1 year ago.
Sorry for all the info after you answered. I entered it when it asked me "what else I had done" but I guess you didn't get that info before you replied.
Expert:  Your Toyota Guy replied 1 year ago.
Reading everything..
Expert:  Your Toyota Guy replied 1 year ago.
Check the red/yellow wire for voltage, specifically 5volt reference.
Expert:  Your Toyota Guy replied 1 year ago.
When the fans should be running of course.
Customer: replied 1 year ago.
I remember checking that also when I was the testing of that section on the cooling fan on vehicle inspection. From what I recall it seemed normal but I will check it again in the morning.
Expert:  Your Toyota Guy replied 1 year ago.
Just let me know what you find.
Customer: replied 1 year ago.
I do remember checking this before I replaced the cooling fan computer and it was part of the reason I actually replaced the cooling fan computer first, but I just checked it again. 5.5 volts with a warm car running but under temp, 6.12 volts with AC running, 9.09 with temp sensor disconnected. The varied rates make me still think the cooling fan computer was bad. The book does not say anything about the voltage going up but it makes sense and I tested it several times and the rates were about the same each time.
Expert:  Your Toyota Guy replied 1 year ago.
Yes, that shows the correct signal from the ECM, you have a bad cooling fan controller.
Expert:  Your Toyota Guy replied 1 year ago.
Did you get the A/C running?
Customer: replied 1 year ago.
replacing the fan control unit, with a 3rd unit did not fix the issue. Still same problems and same symptoms. What is next?
Customer: replied 1 year ago.
Update: I contacted the ebay seller that sold me the original used fan controller (#2) , he sent me another one at no additional charge (#3). The probability of having all three fan ECUs bad is EXTREMELY, EXTREMELY low, as its not a common fail point and statistics would suggest it's nearly impossible. After I put in the new ecu control unit (#3) and it still didn't work i decided to check the red/yellow wire from the main ECU. At the time I believe it was still showing reference voltage like before but still no fans under any circumstance. My wife had complained that there was a high pinched almost non existing ringing noise coming from the computer area ever since I replaced it. Even thought the main ECU I had purchased from ebay was also from a 2008 Toyota sienna SE and it had run fine for the past two weeks I plugged back in the original main ECU and flashed it for 30 min with the "handshake method". The car started fine on the original main ECU but still no cooling fans.Convinced it must be something else I pulled the main power supply plug that goes to the fan ecu control unit and manually plugged each wire into the contacts on the fan ECU, ensuring they were all touching the contacts on the cooling ECU. This actually caused the new unit (#3) to turn on one of the cooling fans (passenger side) whenever I turn on the key to the aux position, even if the AC is off and the temp sensor is plugged in. This is the first I have seen any cooling fans work since this started. The car was cold (67C) however so no fans should have turned on at all. The fan stayed on even if I ran the car for several minutes. I tried the other cooling fan computer (#2) and the same symptoms, just passenger side fan with key to aux. I checked the voltage on the main ECU yellow and red wire, no voltage, even with AC on or Temp Sensor disconnected, now no changes in reference voltage, just zero all the time. I am guessing that when there is no voltage on yellow/red wire the cooling fan computer default is to turn on at least one fan. Figuring that maybe I had blown the AC fuse that was by the main ECU (behind glove box) I checked it, it was fine. I had previously replaced the main Fan relay with a brand new one, but figuring that maybe it was stuck closed I checked it. It was fine. I even switched it out with the original one, and the fan would still turn on whenever I turned on the key. Figuring maybe the #2 fan ECU computer was bad I just put fan controller #1 (original) back in for testing...this time BOTH fans turn on at full blast when I turn on the key with a cold car and no ac and a normal temp sensor plugged in. I seem to have gotten the fans to both work now but now they just stay turned on all the time the key is on.I know what your thinking if you work at a Toyota dealership....why am I using used parts off Ebay? Simple the replacement (Fan ECU #2) was just $35 dollars, and the second one (#3) was free from the original seller. The probability of TWO bad used parts in a row is Extremely low, and now I am not getting any reference voltage so I am not convinced that if I replace the fan ECU at this point with a new dealer one ($300) it will solve the problem.Next I ran a full health check with TOYOTA TIS system to see if I could find anything else. This time TIS it put an asterisk next to the AC system after the test, indicating it could not find the AC system or that something was wrong but did not give more details.Is there anything (fuse/relay) between the main ECU and the red/yellow wire that would cause the wire to have no voltage now? Is there anything else besides a faulty main fan relay (that I already tested/replaced) that would cause both fans to run at full speed as soon as I turn the key to Aux regardless of normal temp/no AC/connected temp sensor? What would cause the red/yellow wire to have no voltage?
Customer: replied 1 year ago.
No reply after two days, that last fix did not solve the problem? If you don't want to answer the questions then please transfer it to someone else as I am nearly 2 weeks into the question....and I don't have a solution yet.
Expert:  Your Toyota Guy replied 1 year ago.
Sorry, internet was down. If the CAN bus could not communicate with the ECU and your signal wire (red/yellow) isn't shorted to ground then the ECU is just not responded and needs to be replaced.
Customer: replied 1 year ago.
Neither computer, the original, or the replacement, is sending signal to the red/yellow wire and both fans turn on full speed as soon as I turn the car to first position. I have looked at all the wiring diagrams and there is only one wire from the ECU to the fan controller computer and it ohms out fine. When the car is running the red/yellow wire almost ohms out to ground (0.2). I can try and replace the ECU with another one as they are only 20-40 bucks on ebay but two computers....and still no signal from red/yellow wire I am wondering if there is something outside the main computer, that signals the main computer to then send signal to the red/yellow wire. I know I can only flash the immobilizer so many times before I run into big there anything besides replacing the main ECU again that would cause the red/yellow wire to send signal? I have checked every fues that is at all related and they are all fine....

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