The problem with the heat pump leading Tesla owners to lose heat in extreme cold and the subsequent software fix that Tesla issued has now been revealed in more detail in the new NHTSA recall.

Last month, Electrek reported on Tesla owners losing heat in extreme cold as some heat pumps were failing.

As we explained, it’s a problem that first emerged last winter with Tesla vehicles equipped with the automaker’s new heat pump system, first introduced in the Model Y and added to an updated version of Model 3.

It was the first full winter for both vehicles.

At the time, Tesla said that it fixed the issue with a software update, but it is now resurfacing a year later in a big way as extreme cold waves are hitting several parts of the world.

Many Tesla owners complained that they are losing heat in extreme cold and several owners who brought their cars to the service center had their whole heat pump system replaced.

A week later, CEO Elon Musk said that a software update to recalibrate a valve in the heat pump system is being released and should fix the issue.

The update appears to have reduced the problem, but there are still some reports of Tesla owners suddenly losing heat.

Now the software update mentioned by Musk is explained in more detail through a safety recall, since the NHTSA determined that the issue was a safety risk due to reduced windshield defrosting:

“Windshield defrost performance that does not fully comply with FMVSS 103 may cause reduced windshield visibility in certain conditions, which may increase the risk of a collision. Tesla is not aware of any crashes, injuries or fatalities related to this condition.”

NHTSA explains the problem in detail in the new recall notice:

“In vehicles built with heat pump, the Electronic Expansion Valve (EXV) may experience controller communication interruptions, after which the EXV driver may attempt to realign the EXV rotor by rotating it in a small increment toward the open direction. When heat pump vehicles delivered with firmware release 2021.44 through 2021.44.30.6 experience such interruptions, the vehicle software does not close the valve, and the accumulation of interruptions and subsequent realignments over extended periods where the vehicle is awake may result in an unintended valve opening event. This, in turn, may trap refrigerant inside the evaporator and may deplete the refrigerant from the active components in the system. The depletion may result in fail-safe compressor stoppage, and cause loss of cabin heating, particularly in temperatures –10 C or colder. While the windshield defrost system continues to operate with the condition present, defrost performance may not fully comply with FMVSS 103.”

The problem apparently only affects more recent vehicles with the heat pump that were delivered with specific versions of the software:

“The recall population includes certain new Model Year (“MY”) 2021-22 Model 3, Model Y, Model S and Model X vehicles built with heat pump and running firmware release 2021.44 through 2021.44.30.6 at the time of customer delivery.”

As previously discussed, Tesla has already started pushing the software fix.

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