Macbook Pro: Fix 4SNS/1/40000000 TsOP by replacing Palm Rest Sensor (fixes fan constantly at 100%)

I recently replaced the keyboard in my MacbookPro 2,1 (this is relevant for most older MBPs, not just the 2,1) by following the steps in this great video:

After I put everything back together the keyboard worked like a champ but after two minutes of uptime my fans would suddenly peg at 6,000 RPM. I tried resetting the SMC controller ( and when that failed I ran the Hardware Test which I would encourage anybody experiencing hardware troubles to do.

The hardware test came back with: 4SNS/1/40000000 TsOP
I expected to find a nice description of this string online, similar to OBD-2 trouble codes in a car or POST errors provided by any PC manufacturer. To my great dismay this list is either not publicly available, well hidden, or I failed. After some Googling I was able to piece together that the 4SNS indicates a sensor failure and TsOP is the palm rest sensor. Read the bottom of this post for a list of other sensors.

Palm Rest Sensor
If you can open up the laptop and find this sensor on your own then you are more clever than I. After some failure the Internet explained the sensor is built into the keyboard/touchpad connector. I’ve used a picture taken from to demonstrate the cable:

This connector doubles as the Palm Rest Temperature Sensor
. This connector is usually taped down onto the motherboard and when I peeled the tape off I accidentally pulled a little bit of the sensor off of it. Resulting in this situation:
The temp sensor has been ripped off the connector

To fix this, the entre connector needs to be replaced. To do this remove the palm rest + keyboard assembly (use the steps in the video above). You will likely have to break some Warranty tape. However, if your laptop is still under warranty you probably wouldn’t be reading this to begin with. Make note of the keyboard backlight connector.

Remember to reconnect this.

If you fail to reconnect this the keyboard backlight won’t work which is probably not so bad but OS X will detect the keyboard as being a newer mac keyboard with different function key layout. So volume up will go from f5 to f12! This mistake had me scratching my head for quite some time.

The final area of caution is the connectors for the power button and magnetic lid sensor. It is glued on to the underside of the speaker grille and shouldn’t be ripped off because it will make installing the new one harder. Instead, pull it up while sliding something under it to break the glue seal.

Be gentle here to avoid damaging the plastic?/rubber? underneath the grille

Installation is the opposite of removal and none of the pictures I took were especially interesting.

Hope this helps.

List of Other Sensors (taken from this list:

  • TB0T Battery TS_MAX Temp
  • TB1T Battery TS1 Temp
  • TB2T Battery TS2 Temp
  • TB3T Battery Temp
  • TC0D CPU 0 Die Temp
  • TC0P CPU 0 Proximity Temp
  • TG0D GPU Die – Digital
  • TG0P GPU 0 Proximity Temp
  • TG0T GPU 0 Die – Analog Temp
  • TG0H Left Heat Pipe/Fin Stack Proximity Temp
  • TG1H Left Heat Pipe/Fin Stack Proximity Temp
  • TN0P MCP Proximity
  • TN0D MCP Digital
  • Th2H Right Fin Stack Proximity Temp
  • Tm0P Battery Charger Proximity Temp
  • Ts0P Palm Rest Temp
Macbook Pro: Fix 4SNS/1/40000000 TsOP by replacing Palm Rest Sensor (fixes fan constantly at 100%)

5 thoughts on “Macbook Pro: Fix 4SNS/1/40000000 TsOP by replacing Palm Rest Sensor (fixes fan constantly at 100%)

  1. Chris says:

    Hi Henry,

    You’d be surprised how insightful this blog post of yours is for Macbook Pro DIY techie newbies! So thank you for sharing.

    I am in exactly the same position you were in with the same error, I too have ripped part of the sensor out.

    Now I know how to repair it I was wondering how or where you got the replacement cable from? Is there a specific part number?

    Thank you.



    1. Hi Chris,

      Unfortunately to my knowledge it isn’t possible to get replacement parts without being an Apple authorized repair shop. I bought a used, broken macbook keyboard on Craig’s list and used the cable from there.

      — Henry


  2. Nikko says:

    I’ve bought mine on ebay. My situation was different as I replaced the old, scratched palmrest of my A1212 with a new-looking palmrest from A1297 thinking they are identical. But after installing the fans went up to 6000RPM with laptop being cold. I ran diagnostics and the palm rest error came up. I was blaming connector, but it turned out that A1297 palmrest was different. So I ended bying the right one off ebay – only fixed the issue where Apple geniuses were helpless, they did not know where the sensor is. Thank you


  3. Martin says:

    Hi Henry,

    thanks a lot for sharing this very helpful information. Had the same problem and replacing the flex cable solved it. Many know what Ts0P stands for but I found no other source describing where the palm rest temp (L) is placed and what to do if a hardware test gives this error information when your mbp fan is running at 6000rpm.
    You can get the cable in some online shops. If you have an early 2008 look for a1260 top case flex cable. I paid 39 euros.



  4. Jorge says:

    Hi Henry,

    For me its clearer than all of that. I got the error of 4SNS/1/40000000:TsOP-128.000 after running the hardware test and after searching the web and following your advice (referred from another pages as well) I though about the trackpad. I have a late 2008 Macbook. Luckily I had another trackpad from a 2009 Macbook Pro, and although the trackpad does not fit in my 2008 Macbook, it has the same connector. I tried to pass again the hardware test, and surprisingly the error was still there. Then I just remembered that I had recently switched my old HD for a new brand SSD, and I changed back again the disc to my old HD. With the old HD I ran again the hardware test and voila! the error has been gone.

    Therefore, the conclusion is that such sensor is somehow installed within the HD hardware, and that’s the reason why everyone who has replaced the HD by a non-Apple SSD is unable to read the SSD temperature with any software (iStat or whatever…).


Comments Disabled

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s