How To Fix The 4SNS/1/40000000: TB3T-128.000 Macbook Error

Some people have run the Apple Hardware test on their Apple computers and have run into the error message 4SNS/1/40000000: TB3T-128.000. This is especially an issue on the unibody aluminum Macbook Pros.

According to Apple this error message refers to the sensors inside the computer, specifically the battery temperature sensor.

In order to resolve this issue try one of the following fixes:

Fix #1: Reset your Mac’s NVRAM

The NVRAM in your Mac is a special type of memory that stores certain settings in order to give your computer quick access to them. Sometimes these settings may become corrupted or wrong. By resetting your NVRAM you can bring these settings back to how they were when you bought your computer.

To reset your NVRAM:

  1. Turn off the Mac.
  2. Press down the following keys: Command (⌘), Option, P, and R.
  3. While still holding down the four keys turn on the Mac.
  4. Hold the keys until the computer restarts.
  5. Release the keys.

Once the computer boots you might need to correct your timezone or screen resolution settings. Run the Apple Hardware Test again to see if the 4SNS/1/40000000: TB3T-128.000 has gone away. If it hasn’t then move onto the next fix.

Fix #2: Reset your Mac’s System Management Controller (SMC)

The System Management Controller (SMC) is a system on your Mac computer that controls various battery and system functions. Sometimes it needs to be reset in order to fix error messages like the one you’ve run into.

The process of resetting the SMC is easy however it differs depending on whether you have a macbook with a battery you can remove or a macbook with a battery you can’t. I’ve provided steps for both, choose the correct steps for your computer.

To reset the SMC for a macbook with a battery you can remove (such as the plastic Macbooks) without opening the case:

  1. Shutdown the Mac. Disconnect the power cord. Remove the battery.
  2. Press and hold down the power button for ten seconds. Then release the power button.
  3. Put the battery back in and connect the power cord. Power up your macbook.

To reset the SMC for a macbook with a battery you can’t remove (such as all the unibody Macbook Pros and Macbook Airs):

  1. Shutdown the Mac. Make sure that the power cord is connected and charging.
  2. On the Macbook’s keyboard press and hold the Shift-Control-Option keys on the left side (has to be left side) as well as the power button at the same time. Hold for five seconds.
  3. Release all keys and the power button.
  4. Turn on the Mac.

Fix #3: Have you recently replaced your battery?

If you have a unibody Macbook Pro on which you have recently replaced the battery with a new one then this error is something you can ignore according to Apple. Multiple users have reported that Apple is telling them that this error message is completely normal to have after battery replacement especially if you have a mid 2009 Macbook Pro.

You can always bring the machine to an Apple store so that Apple can their specialized software on it to make sure nothing is wrong but you can probably safely ignore the error message. Many others have. Speculation says that the error has something to do with the Macbook getting confused with a newer battery design thus producing a false positive error message. But the battery and the Macbook Pro should work fine.

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