Two-Thirds Of Early Tesla Model S Drivetrains May Fail By 60,000 miles

Survey data collected by Plug-In America from current early-model Tesla Model S owners has predicted that up to two-thirds of early model electric-drive units may fail by 60,000 miles. If their predictions are even remotely accurate, that's bad news.

Despite the all-electric Tesla Model S being so impressive, even breaking Consumer Reports' review scale, it is known that early production years of the car have had a decent share of reliability issues. This isn't too surprising, as Tesla is still a young automaker. The company reported in November a drastic reduction of these issues (by 50 percent) in their more-recent model years.

Improvements aside, those early cars still face issues that first and second-hand buyers — and ultimately Tesla — are going to have to deal with, with a recent study conducted by Plug-In America — a neutral and non-profit party — claiming up to 66 percent of earlier model-year Model S drivetrains are likely to fail by 60,000 miles based on consumer-reported data.

As reported by Green Car Reports, the sample data was run twice, taking two different approaches to the information they collected from early Model S owners. The analysis covered 327 respondents to the survey in October, or about one percent of 2012 to 2013 model year owners. 43 respondents were later model year (2014+) owners. The owners were asked about the mileage of their vehicles, their ownership experience, whether or not their car had received a drivetrain swap, and if so, the mileage at the time of the repair.

The data was then collected and processed using a Weibull statistical analysis for probability distribution, which estimates reliability lifetimes. Essentially the analysis looks at the failures and non-failures of, in this case, specific wear-and-tear components of the vehicles and produces a value for failure rate. The results map out the lifetime reliability of the components providing a probability for the survival rate for vehicle drivetrains that haven't yet failed.

The study concluded that 77 drivetrains had failed compared to 250 "suspends," or samples that haven't yet failed.
The results of the second study were based on only the final odometer reading, and not the reported reading at the time of the maintenance, for those vehicles that had received a swap. This adjusted for "transcription errors" in the data sample. The results are as follows:

The reliability engineer was careful to emphasize that the results were only valid if the data was correct, had no selection bias, and was random. While selection bias was definitely in play (only those customers who knew about the survey could choose to fill it out) the sample covered more than 1 percent of the total population of 2012 and 2013 Teslas (327 respondents for about 25,000 vehicles). Jalopnik

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