In this video I have a look at a Chevy Trailblazer that is having some problems with the electronic viscous fan clutch. Seems like a silly design for a cooling fan but it is pretty easy to diagnose once you know how it works. -Enjoy!
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49 thoughts on “Chevy trailblazer: electric fan clutch failure”
  1. Avataaar/Circle Created with python_avatars DanChasingTheGlobe says:

    The MIL code also might have been "P0495 Powertrain". I have a 2003 Trailblazer with this issue: "cooling fan stuck in high speed throwing P0495 no matter what the Chevy dealership service department tries to do." This issue is very frustrating. You'd think the brand's own dealership service department would be able to fix this issue. But so far, no luck there. And it is all luck at this time.

  2. Avataaar/Circle Created with python_avatars andrew Wiebel says:

    Great video. I have a 03 trailblazer no crank no start. Code say cam and crank shaft sensors and also throws a code for this. Can this cause the trailblazer not to start. Hope all is well stay safe

  3. Avataaar/Circle Created with python_avatars THE BOOGYMAN says:

    I jus replace it.. if it needs it, I use hayden fan clutch better then OEM 🤷🏻‍♂️

  4. Avataaar/Circle Created with python_avatars Bill Keeton says:

    Will that unplugged cause it to not accerate

  5. Avataaar/Circle Created with python_avatars Brad Hatt says:

    What kind of scan tool do you need to do this test? Are there any affordable scan tools that can do this? $500 or less area

  6. Avataaar/Circle Created with python_avatars Antonio Figuera says:

    Mi hermano soy de VENEZUELA, mi ventilador despues que se retiro el radiador para su reparacio y coloco nuevamente el fan cluch al inicio prende normal pero llega el tiempo que se apaga, se queda parado, no gira y el carro me sube la temperatur, que puede ser? gracias

  7. Avataaar/Circle Created with python_avatars Isshman Garcia says:

    Great video as usual. Per GM service info: The desired RPM vs the actual RPM will NOT always be identical. It states that as long as they are within 800 rpm of each other, that is normal. Also code for this diag would be P0526 Fan Speed Sensor Circuit.

  8. Avataaar/Circle Created with python_avatars Matthew Sewap says:

    Hey ERIC O.
    This is a radiator fan related issue. The question is, I do not have any communication with the ECM on a 2004 Nissan Altima. Scan tool didn’t work. Was able to read data stream for the related part. Everything seems normal. Until I did my checks. When I disconnected the ECM relay. The radiator fan would go on automatically on its own. Key on.. but no power on ECM related components. I’m thinking is it a short? Ohh!! Aftermarket security/auto start has been added. Seen two open wires hanging from the obd2 connector from aftermarket splice. Help would be greatly appreciated 👍🏼

  9. Avataaar/Circle Created with python_avatars 2002 6 cylinder TB LS says:

    So is the desired speed and actual speed suppose to always match?

  10. Avataaar/Circle Created with python_avatars JUELZ G DO says:


  11. Avataaar/Circle Created with python_avatars 10 bears says:

    I have a 2003 Chevy TrailBlazer 4.2 I'm adding electric fans out of a 2010 Chevy Impala. I would love to hook it up to the factory harness that controls the fans is it possible to do so??? Please let me know ASAP. Thank you

  12. Avataaar/Circle Created with python_avatars Lucan Ericksen says:

    You still didn't show me how to replace install the circuit fan speed sensor.

  13. Avataaar/Circle Created with python_avatars Quaker Wacker says:

    this is my go to guy defiantly has basic sense thanks for real\

  14. Avataaar/Circle Created with python_avatars Bob Smith says:

    Practical symptom: When you drive the car, it sounds like the transmission is failing to upshift, and the engine is racing. Check the fan clutch before sending it to a transmission shop. Most of them will rebuild the transmission even if it's good.

  15. Avataaar/Circle Created with python_avatars fat jack says:

    Hi I got a 2003 blazer an I change the fan clutch every 6 months it goes out sometime my end side lights will flash 3 times when I'm in side sometime what u think. . Joe

  16. Avataaar/Circle Created with python_avatars Robert Threm says:

    If you unplug that wire should that fan run full speed?? It's a new clutch .. but it could be junk they bought it on line

  17. Avataaar/Circle Created with python_avatars Callie Stahl says:

    How do i fix the fan sensor on my trailblazer?

  18. Avataaar/Circle Created with python_avatars Josue Martinez says:

    So how do you fix the problem with the speed sensor?

  19. Avataaar/Circle Created with python_avatars z says:

    how is the car driving when the fan is doing this? my fan is doing this and i have almost no acceleration. if i go up a hill i will either stay the same speed or lose speed. if the transmission downshifts to grab a lower gear at about 50 mph and above, the rpms increase to accommodate the lower gear, but rpms do not increase with throttle, and speed does not increase. the only thing that happens when it downshifts is i lose miles per gallon.

    again, i would love to know how the car is behaving when you know that this fan is bad because i am tired of driving with my hazards on everywhere.

  20. Avataaar/Circle Created with python_avatars Shane Harrison says:

    I've seen those fans many times didnt think they put them in the trailblazers

  21. Avataaar/Circle Created with python_avatars Erika Yates says:

    When do you fix it???,

  22. Avataaar/Circle Created with python_avatars Julio Luna says:

    my 2002 trailblazer just got a new fan clutch 3 days ago, but it only kicks in when my temp gauge is at 3/4 then it comes back down, exactly just like the prior fanclutch, so im guessing is not the fan clutch at all, also , weird thing no trouble codes detected, but when it kicks in at 3/4 temp comes down fast, what could it be? what else can i test? new water pump, new fan clutch, clean radiator , the only thing I have not replaced is the coolant temp sensor

  23. Avataaar/Circle Created with python_avatars Ted Crawford says:

    Eric can you put up that operation of the fan clutch system so I can have a copy of it ?

  24. Avataaar/Circle Created with python_avatars Notcha Grandpa says:

    Eric's the man, if he can't diagnose your vehicle's problem, well chances are you don't have a vehicle.

  25. Avataaar/Circle Created with python_avatars William Smith says:

    After you replace the Electro hydraulic fan clutch assembly you have to update the PCM with new software for it. Do the reprogram. You have to do the reprogram

  26. Avataaar/Circle Created with python_avatars Joe Vreeland says:

    Since I "retired" in 2004, and I only run into these problems by accident (I actually own a gifted-to-me-by-son really neat-o '05 Trailblazer) – I wonder if I could just go right to the signal from the Hall Effect Unit on my scoping handheld from years ago?
    It has the ability to show digital and analog pulses/voltages – and it should be able to do what you can do with a Snap-On multi-channel unit — right? I was contracted with Chilton Repair until I retired too, but I've downloaded every schematic I could find from various sources and I THINK I'm somewhat armed for whatever comes my way.
    I have nothing bad to say about Snap-On – but I'm 75 years old and I cannot see a new handheld paying for itself for another 5-6 years even if I went back to work full-time (which I am NOT going to do!). I've still got my Snap-On MT2500 Brick and up till now it was fine!
    Hmmmmm – I wonder if something like Torque Pro would be a good investment? Not sure it's bi-directional except for code redacting – but I'm kinda leery about CAN and The Brick getting along and playing nicely.
    BTW – I have sub'd your site and I follow everything that I think I MIGHT run into —–> when the trout aren't calling that is.

  27. Avataaar/Circle Created with python_avatars Robert Threm says:

    Tell me if I unplug the fan should it be stuck in high. It's a new clutch fan the other had a bad bearing

  28. Avataaar/Circle Created with python_avatars QQTrick1QQ says:

    Thanks Eric O, the right video at the right time for my situation,

  29. Avataaar/Circle Created with python_avatars Vick G says:

    So what did you replace?

  30. Avataaar/Circle Created with python_avatars Otis says:

    Fantastic! 😉

  31. Avataaar/Circle Created with python_avatars David Nguyen says:

    Bruh, where is the intro Mozart music?

  32. Avataaar/Circle Created with python_avatars Robert Kohut says:


  33. Avataaar/Circle Created with python_avatars Jay Beezy says:

    Nice title. Whitty you know. Great stuff. I watch from palmbeach florida. No cold here though ever. Iguanas all over

  34. Avataaar/Circle Created with python_avatars Michael Wilder says:

    My local shotgun mechanics would have just changed the Fan Clutch with no testing at all! Your testing causes minimal comebacks at South Main Auto!

  35. Avataaar/Circle Created with python_avatars Abdullah Yahyai says:

    Thanks for that video , I’m currently having the same problem on a 2006 LR3 with code P0480 . Replaced the fan but no improvement. Hooked my original fan on to another LR3 and the fan ok . So now I now the problem if not from the fan but it will somewhere from the connector at the fan to the ECU . And here where I’m lost . I got the wiring diagram for the fan , but I don’t have a scope to check the wave form , I’m using a maxisys P809 as scantool and a good multimeter. Any tips Will be much appreciated .

  36. Avataaar/Circle Created with python_avatars Mister Mechanic says:

    Eric, So many comments… Own a 2002 TB with 160K trying to keep it operational for few $. I would just like to convert the damn thing to a bi-metal fan clutch like on my 2000 s10 with 4.3 v6. They attach to water pump similarly. or maybe remove it all to together and add an electric fan. any consequences to vehicle operation other than the check engine light? Thank you. If I must replace this with new, do you recommend a certain manufacturer of replacement parts?

  37. Avataaar/Circle Created with python_avatars William Smith says:

    When I was working for Chevrolet at the dealer level, we saw so many of these coming in and the customers were complaining that it was a transmission issue . It sounded like a jet airplane thought that because of the fan noise would increase with the speed of the car, like direct drive, but we knew we had to put a new electric mechanical fan clutch assembly on it and also reprogram the PCM for the new fan clutch assembly. I believe there was a TSB on this.

  38. Avataaar/Circle Created with python_avatars Michael Mankowski says:

    Very interesting. Didn't know that there was such a thing. Great video.

  39. Avataaar/Circle Created with python_avatars big27man2009 says:

    My 05 envoy with 115,000 miles is throwing a code for the fan as well. Gonna show this video to my mechanic and tell him if he can do it you can do it

  40. Avataaar/Circle Created with python_avatars Master Debater says:

    Well that fuel pump is toast now! Who brings a vehicle to the mechanic with no fuel in it…

  41. Avataaar/Circle Created with python_avatars Art Mont says:

    Makes it way easier to change that fan clutch with that demolished fan shroud

  42. Avataaar/Circle Created with python_avatars Lackey DeHackey says:

    Just like PWM on the HVAC blower only with a sensor instead of human and knob. BTW Eric, the sensor on that fan works like the one in the reformatted hard drive PC. 3 wires, 5V ground and a PWM output to see if the fan is working. Had to reprogram one when they changed fan models.