Many Tesla owners reported problems with the rear drive units on the Model Y and Model 3. A new generation of the drive unit is now installed on vehicles built at Giga Texas and possibly other gigafactories. A recent teardown shows what changed for the fourth generation.

The love-and-hate relationship many people have with Tesla is a show to watch. Many complain about multiple issues with their cars, but say they still love them. Others have quality and manufacturing problems and are annoyed by incompetent Service Center technicians, but still love the brand. And others just hate everything about Tesla without having a reason for that, probably not even owning a Tesla.

We must admit that build quality is not always solid, and many cars deliver with misaligned body panels, badly installed components, and other issues. Most of them get sorted out post-delivery. It's possible to have a poorly-assembled car and still enjoy it without issues for years. Still, poor build quality indicates bigger manufacturing issues that could cause problems down the road. One example is the dreaded rear motor failure that many Model 3 and Model Y owners have complained about.

This is an intriguing issue, considering that Tesla has been making drive units for quite some time. You'd expect to have sorted out problems by now. Still, we can't dismiss Tesla's resolution to optimize costs. Sometimes, a bad engineering decision can lead to costly repairs. That's why car recalls are not unusual. Tesla has not issued a drive unit recall yet, but we know it changed the design of its rear drive unit several times.

A teardown by Ingineerix revealed that Tesla is now installing the fourth generation of the rear drive unit in the Model Y built at Giga Texas. This should fix the problems reported with the previous units, or so we hope. At first sight, Tesla has made the new unit more efficient, easier to manufacture, and potentially cheaper. It also installed a new inverter that is more compact and efficient while baking in more safety features. Instead of temperature sensors, Tesla uses infrared sensors to measure the temperature in various inverter parts.

The first obvious thing is that the new drive unit has a new oil filter cartridge that is not user replaceable. This might indicate that it should last the car's lifetime, cleaning the cooling fluid of small debris from the unit. Opening the motor reveals the new hairpin stator that Tesla discussed during Investor Day on March 1. Besides being more efficient, the hairpin stator is much simpler to manufacture because everything can be automated. It's the opposite with fine copper wires, which must be manually wound in previous stators.

We're sure this would have been a teardown that Sandy Munro would have loved to do, but the timing wasn't right. The fourth-generation drive unit appears identical on the outside to the older units, so they can be used as replacements without problems. This indicates that the Tesla Model 3 might get the new motors soon.

Tesla recently disclosed in its Impact Report 2022 that its battery packs retain 88% capacity after 200,000 miles. Several people took that at face value and as a reassurance that they could drive an EV for a long time without issues. Having covered so many situations of battery pack failures from Tesla, I felt obliged to put what the report disclosed in the proper context – one that contradicts the BEV maker.

If battery packs only lose 12% of their capacity after 200,000 miles, why are so many of these components failing in 2012 to 2015 Model S units? Why have so many failed – even if still under warranty – in more recent vehicles? On February 7, I wrote about the BMS_u029 and got back to the subject on April 19 to discuss other errors that indicate a battery pack has reached the end of its lifespan. The Facebook group dedicated to these warnings keeps growing, and the members did not take that part of Tesla's report very lightly. They are living proof that the BEV maker should – at the very least – phrase its documents in more careful terms.

When you check that part of the Impact Report 2022 (page 39), you can see that Tesla used the Model S and Model X as examples. However, it refers to their packs as "our batteries," as if all of them were the same. They are not: the battery packs on the Model Y and Model 3 use different cells. Their battery management systems (BMSs) must also have improvements and other technical solutions. Not even the chemistry is the same on all battery packs.


Let's imagine these battery packs were all identical. If that were true, all Teslas would be subject to around "six different types of pack failures." This is what Jason Hughes – aka the Tesla Hacker – said when he commented on the water-ingress problem that has destroyed several Model S battery packs so far. Tesla never acknowledged that. Instead, the company wrote in its report that people frequently ask it if they will have to replace these components in their BEVs "at some point in the future." According to the BEV maker, "the answer is no."

If Tesla were a person, I'd dare them to say that to the face of the several customers who had to replace their battery packs – whether under warranty or from their own pockets. The list is long. Take only the Facebook group I mentioned: it had 165 members when I started writing this and already has 169. Companies were created to provide remanufactured battery packs to Teslas because the number of vehicles that would need one was relevant. How can Tesla say that "the answer is no"? Only if the question was different. But it gets worse.

The BEV maker wrote that it estimates "that a vehicle gets scrapped after approximately 200,000 miles of usage in the US and roughly 150,000 miles in Europe." It only failed to mention why that happens. Usually, it has to do with engines that die and are no longer cost-effective to repair. Besides, governments impose restrictions to keep them running because they pollute a lot more than newer ICE vehicles. None of that applies to electric cars: only safety issues would be a valid excuse to remove them from the streets.

Bear in mind that Tesla's lawyers told a German court its cars should not last more than 130,488 miles (210,000 kilometers). Elon Musk said in 2019 that "the current battery pack is about maybe 300,000 to 500,000 miles." Who should you believe? The company seems to wish that you trust it and its CEO before purchasing its cars and its lawyers after the deal is sealed. It could be the opposite: believe Tesla's lawyers before buying its vehicles and the company and Elon Musk in court.


What about believing the Impact Report 2022? Stick to its fine print. At the bottom of page 39 of the document, you can read this:

"Mileage is only one factor in battery capacity retention; battery age is also a major factor. Retention figures at lower mileages above likely reflect the impact of age, while higher mileage values, which come from high-utilization vehicles, likely reflect less influence from battery age. Performance of newer chemistries (not yet shown here) can vary, and we plan to expand disclosure once we have sufficient data."

There you have it: Tesla itself admits the Model S and Model X battery packs do not reflect the conditions that all these components made by Tesla will offer in the future. That said, there is no sense in talking about them as if they did. At best, they offer hope that the newer battery packs can perform in the same way – but that is not for sure. However, that is not the most critical part of the fine print.

The BEV maker acknowledged there that "battery age is also a major factor" in capacity retention. That said, it is only logical that a component that loses performance as it gets old will have to be replaced "at some point in the future." That's unavoidable. As I wrote on March 9, batteries are wear parts in most pieces of equipment that use them unless these gadgets are designed to last as much or a bit less than their cells, such as mobile phones. That's what Tesla seems to be saying about its cars.

Let me rephrase that in the most straightforward way possible: Tesla seems to hope that its cars will end before their batteries do. Sadly for the company and even more for its customers, that has not been the case. Whether due to mileage or age, these buyers eventually receive a hefty estimate for a battery pack replacement.

Bob Atkins is a good example. He replied to a Tesla tweet talking about the Impact Report with a compelling example. Sharing pictures of a Model S with 43,280 miles with the BMS_u029 error, he stressed that "people need to know that older Tesla cannot be judged in value based on mileage or appearance."


According to Atkins, "the vehicle can appear to be totally flawless and have low mileage and then without warning could become disabled and require a $20,000+ main (HV) battery replacement." No external signs show if a battery pack is in a good state or about to fail. The Tesla customer also shared the invoice for this Model S repair: $18,000 for a new battery pack. It also needs new bolts ($25.92) and labor ($502.25). Include taxes, and the final value to pay is $20,375.83. That's enough to buy a smaller new ICE car or a used one. According to KBB, a used 2012 Model S Performance costs between $22,235 and $25,918.

If we did like Tesla's Impact Report and only considered that battery packs age in the fine print, we'd state that these components would only lose 12% capacity after 200,000 miles. That would mean a high-utilization vehicle would confirm what the BEV maker said regarding battery pack replacements, correct? Ask Hanjörg von Gemmingen about that.

If you have not heard about this German Tesla owner, he was the man who drove a Model S for one million miles. If the capacity loss were linear, a battery pack would have lost 60% of its capacity going that much, which is well below the 70% under which most car companies pledge they will replace a battery pack under warranty. Counting once again with a linear capacity loss, Von Gemmingen would have needed two battery packs to complete one million miles – one for every 500,000 miles until they reached a minimum capacity of 70%.

The bad news for the BEV maker is that he did that with three battery packs, with the first two replaced under warranty. The first failed when the car had 290,000 km (180,197.7 miles) on the clock – below the 200,00 miles with which the battery pack would still have 88% of capacity. Von Gemmingen drove with a temporary second battery pack for 150,000 km (93,205.7 miles) until it was replaced with the third one, which has lasted almost 727,000 miles (around 1,170,000 km) so far. One battery pack contradicts Tesla, one exceeds what it promises, and the one in the middle did not have time to prove anything. Until we have more examples, we can call it a tie.


Von Gemmingen also used "11 or 12" motors, but that's another story. When the warranty ended, he purchased a Lucid Air. It would not be economically feasible to pay around $20,000 each time he had to replace the battery to keep on driving that BEV.

That puts the idea that battery pack replacements will not be necessary to rest. If you are buying an electric car with the idea of keeping it for several years, prepare yourself to eventually replace the battery pack or to keep trading it in for a newer model before the warranty expires. That's probably what Tesla expects you to do. Just don't tell me this is the most environmentally-friendly attitude to have: the answer is no.