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wrote:

IT IS A BIOS FLAW! WHAT THEY NEED IS A BIOS FIX

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Excellent English.  :smileyvery-happy:

Wow, it was un-wanted, but now I can really see the irony behind it. Laughing for the unexpected amusement ;)

I guess that updating to the fan control mechanism by lifting up the thresholds would benefit everybody. It would surely help you people using the discrete GPU when docking. Lenovo, why you never tried it? I would gladly volunteer using a BIOS with higher thresholds as a beta-tester, my warranty is almost over so you don't have to worry about complaints. Can we have an EC with higher thresholds? Why is it so difficult? Why nobody answers? At least say no, we think it's dangerous. In such case users will know that somebody there is still alive!

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wrote:
No it doesn't rule out the GPU.

One group of us has their fan constantly stuck at 4000 rpm event at low temperatures.

The other group, myself included, only has the high fan noise issue when using the dock and/ or connected to an external monitor using dvi/ dp where the idle temperature can't go lower than 47C due to the nvidia chip being on 100%.

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Sorry X2222.  I was hoping something finally got ruled out.  My bad.

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wrote:
Since it appears that there are a few different problems with the T420s fan noise, perhaps it would help Lenovo if one person put together one post with the different types of fan issues that users are experiencing.

The issues that people are experiencing are almost identical and reproducible. Perhaps it would help to have one post that makes this clear to Lenovo. Any volunteers to organize this info?

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You are correct that there are two distinct subgroups of users experiencing the fan noise problem. One subgroup has the nVidia GPU and experiences fan noise along with high temperatures while the GPU is busy, while the other subgroup (my subgroup) goes through long periods where the fan is on full-speed constantly, even with low (<33C) CPU temps. The latter subgroup may benefit from a BIOS fix; the former subgroup is probably out of luck because the fan is simply underpowered for their configuration. In both subgroups, the vacuum-like fan sound of the T420s -- much worse than any other Thinkpad I've ever used -- makes the problem unbearable. (If the T420s fan sounded like an X40 or T61 fan, we wouldn't be having this discussion).

Unfortunately, the issues are not completely reproducible. :-( At least with the latter subgroup (without the nVidia GPU), the system will randomly go through periods where the fan works as intended, and then go through periods where it's at 4000RPM regardless of system activity. Lenovo engineers have failed to describe the intended behavior of the fan to us (temperature inputs and thresholds), so we're unable to devise a testcase that would determine if there's a reproducible bug.

TPFanControl helps, but it causes other problems with the system. It's incompatible with the Lenovo power manager, and if you uninstall the power manager, the battery meter starts going haywire.

Some users report that the problems worsened with a recent BIOS update. This is because there was a third fan noise problem ("pulsing" fan sound and/or frequent fan speed changes), and it seems that Lenovo fixed this one by making the fan blow at a higher (but more constant) speed. This also explains why some BIOS revisions were labeled as fan speed fixes but didn't fix the problem.

I assumed the Lenovo engineers were ignoring this issue because the T420s is an old model by now, but I looked at the Lenovo store today and discovered that Lenovo is still selling this system (!!!!) I wonder if anyone at IBM is annoyed by this problem -- back when I worked at IBM, we all had Thinkpads. Our best bet might be for an IBMer to get annoyed enough to harass someone on the Thinkpad team via Sametime and get some solid troubleshooting tips...

Just for reference -- out of nearly 1000 posts on this thread, here's the only information we've gotten from engineering (post 703) regarding the desired fan behavior:

1. System idling at desktop on AC or battery - will usually run fan speeds between 0 and 2k RPM - this is base on several thermal sensor placed on the system board.

2. When the system is attached to an external monitor and LCD - this causes increased graphic processing from the system video chips and will cause the fan to run at constant higher speeds - ranging between 2K and 4K RPM

3. When using with two external monitors - the increased video requirements push the thermal profile to keep the fans spinning at highest RPM.

It seems that G560 and G570 users are also experiencing the fan speed problem, which makes sense, considering they share some (or all?) BIOS code:

http://forums.lenovo.com/t5/Lenovo-3000-and-Essential/Lenovo-G560-problem-with-fans/td-p/295622

http://forums.lenovo.com/t5/Lenovo-3000-and-Essential/Replacing-G570-fan/td-p/406891

Having just received my new T420s a few weeks ago (replaced an X301) AND having already had the fan error, whcih required an escalated, on-site repair to get Lenovo attention, I looked at this forum first when the constantly running fan feature became apparent.  Seeing that there are 900+ entries, it looks as if Lenovo has no intentions of delivering a fix.

My experience with vendors is that unless there is a financial impact upon them, not much can be expected, so i suggest we start hitting the other forums and magazine sites.  It's unfortunate as the T420s is a really nice product, but lack of attention to an obvious bug deserves more aggressive behavior.

After months of waiting for BIOS or software fixes I called in Lenovo NBD service this week and told them about the problem. In my case the fan starts spinning at 4K when performing low load operations (browsing, checking mails) and when I start a game, it the temparature goes up to +90 degress and the fan spinning at 4500rpm (almost can't cool the CPU down). They sent a service engineer to replace the fan and the thermal paste. When the engineer opened the T420s I asked him if he could find any reason why the CPU gets so hot when the fan is spinning at max. speed. He said that the thermal paste was applied correctly and even the fan was mounted properly (maybe a little bit too loose, but still OK). So now the only thing left could be BIOS or bad design. Considering that this thread is almost one year old, I guess the last one applies.

I sent in my T420s and it was returned on February 29th. Informative updates from Mark_lenovo were:

"""We have it and have made a bit of progress. We pulled out the Linux drive and set aside for safe keeping and installed a Win 7 factory preload drive. Initially all was well, but after applying all Windows updates and applicable Lenovo updates, we are seeing the system CPU temp increase while idle and then the fan ramp up and run at higher speed, and then would settle back down. The engineers are still testing. """

and:

"""The engineer has ordered a replacement system board and fan and will change them out on your system so we can return it this week. We can then keep the parts. """

My T420s with new system board and fan has actually been performing better, though it is not fixed.

On battery, the fan will modulate up and down, though it can still get stuck at 4000 rpms after a while. However, it used to shoot straight to 4000 rather promptly, so it is an improvement. I do see ~3600 rpms some times.

On AC, the fan is still apt to get stuck at 4000 rpms.

Has anyone noticed that even at 4000 rpms, the air is not blowing particularly strongly?

Interestingly, last night I ran powertop and it listed the fan (at 4000 rpms) as the biggest power draw. Since the return of the laptop, I investigated some Linux powersaving options mentioned earlier in the thread. I was not scientific about it, so I don't know if that was a factor in improving the fan on battery. Mainly, I think I just installed tlp and updated to a 3.2.9 kernel with the ASPM fix. They helped extend the battery life, so I am more likely to run off battery. That made me wonder if the power consumption rate is a factor in the BIOS fan control. Prior to improving the battery life, I was more likely to run off AC which did the 4000 rpm thing.

FYI, my T420s has integrated graphics.  BIOS version 1.30. It was originally manufactured in April/May 2011, but I am not sure of the replacement system board and fan dates.