Life with Tesla Model S: replacing the drive unit (aka ‘the funny noise’)Life with Tesla Model S: replacing the drive unit (aka ‘the funny noise’)

Back in 2014, Tesla had a spate of problems with the drive units in early-production versions of its Model S electric sedan. 
(The drive unit is essentially the car’s power train: electric motor, inverter, and gear box.)
High-profile multiple failures occurred in long-term test cars driven by Motor Trend magazine and the automotive website Edmunds.
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Dozens of owners also  reported multiple failures; one guy says his drive unit had to be replaced five times in the first 12,000 miles.
Fortunately, my 2013 Model S, an early production model delivered the same week as the Edmunds car, had no problems.
In most cases, the drive units didn’t actually fail, but simply started making funny noises. Proactive service centers, eager to keep customers happy, were replacing drive units at the drop of a hat—in some cases unnecessarily, according to Tesla CEO Elon Musk.
Onsite service by Tesla Motor technicians on 2013 Tesla Model S, upstate NY [photo: David Noland]
Tesla quickly identified the two primary issues that were causing most of the noises and failures, corrected them, and then announced an eight-year, infinite-mile power train warranty that included both drive unit and main battery.
Since then, drive unit problems have receded into the background. 
The funny noise
But about a year ago, with 60,000 miles on my car, I started to notice a very faint humming/buzzing sound coming from the rear  whenever power was applied.
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Over the year, it seemed to grow progressively louder—to my hyper vigilant ear, at least. But the perceived increase was so gradual it was hard to tell whether it was real or imaginary. In any case, the noise was so faint that passengers rarely noticed it.
I figured the tepid buzz didn’t rate a special visit to my Tesla service center, in Paramus, New Jersey. I decided to wait till my next regularly scheduled service visit to have the noise checked out.
That happened in January, with my annual cross-country drive to California approaching and the odometer at 75,000 miles.
Tesla Model S at Supercharger site in Ventura, CA, with just one slot open [photo: David Noland]
Instant diagnosis
I brought the car in for the scheduled service and mentioned the noise to the service rep. She summoned a tech, who took the wheel as we made a quick spin around the block.
My noise, he concluded after a minute or two,  was the infamous “milling” sound that had become all too familiar to Tesla techs over the years.
“Congratulations,” he said brightly. “Looks like you’re getting a new drive unit.”
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The replacement would cost me nothing, and the car would be ready in two days.
And so it was.
More efficient?
My car is now utterly silent underway, with nary a hum, buzz, whine, whistle or any other auditory evidence that 270 kilowatts (362 horsepower) is churning away back there.
2013 Tesla Model S in Florida, during New York to Florida road trip [photo: David Noland]
Perhaps it’s my imagination, but the car seems a whisker quicker with the new drive unit.
And the new drive may also, possibly have improved my energy efficiency.
In the past, the 120-mile round trip from my home in New York’s Hudson Valley to New York City has typically used 290 to 295 watt-hours per mile in warm weather.
On a recent 60-degree day with the new drive unit, I was surprised to clock 281 for the trip.  
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That’s a promising sign, but more trips will be required to confirm this apparent efficiency gain.
In the meantime, I figure the resale value of my Model S probably just went up a little.
I’ll take it.
EDITOR’S NOTE: An earlier version of this article incorrectly said Tesla’s powertrain warranty was 10 years with unlimited mileage. The correct length is eight years, with unlimited mileage. We have corrected the article and apologize for the error.
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