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Rear Drive Unit Failure DI_w126 Alert

On 9/11/21, I was driving my '16 Signature Model X P90D (~31,000 miles) about 50 mph on a country road a mile from my home. No heavy acceleration, just cruising along. My X started lurching and I got a DI_w126 Alert: "Reduce Power. Service Required." The car became unresponsive to the throttle, and I was lucky to limp home (through a busy 4-way intersection) with minimal throttle control. The car died in my driveway. Two days later, I was able to back it onto the street for towing, where it died again in the middle of the street with a "Rear Drive Unit Failure" alert.

I took a 400 mile round-trip two weeks before the failure with no issues at all. The car then sat in the garage for a week with one or two 2-mile round trips. Then, a fatal failure on the RDU out of nowhere under gentle driving conditions.

My X was towed to the Vallejo, CA SC on 9/13. (The tow truck arranged by Tesla showed up with a flat tire on the dolly carrying the rear wheels of my X. Another unhappy story.)

After several days of "customer engagement by tweets" through the app (and no other way to discuss the problem) the SC determined that there was "a low megohm reading" in the rear drive unit (RDU), the car's controller caught it and disabled the RDU, and it had to be replaced under warranty. After 17 days in the SC, the work was done (waiting for parts, as usual) and I picked up my X. No details on the failure that cost me 19 days without a car.

I realize that the SC probably has neither the time nor the expertise to diagnose failures like this. But, I would like to know what happened inside the RDU and if it is a common or very rare failure. "Low megohms" is not a satisfactory explanation. I suspect an internal short, but how could that happen? I used to think that almost nothing on an automobile is more reliable than an AC Induction Motor.

Does anyone know what happened?
 

vangogh

Member
Sep 4, 2015
371
199
Sunnyvale, Ca
I have a signature 2016 X (65k miles) and a couple weeks ago, I got a warning "car may not restart/service required" and "max acceleration and speed reduced". I called Tesla service and they said it was likely a battery issue, but after a week of diagnostics, they said I need to have my rear drive unit replaced. I searched the web and found a number of interesting videos on early S rear drive train issues, Seems to be many causes for the failures... One was a degradation/breakdown of a Cu gasket in the drive unit that normally allows a current path. Don't know if this is what happened to your (or my) unit. I will inquire about the specific failure on my X when I pick it up and post if they give me any additional info....
 
Thanks vangogh. I think we corresponded in ‘16 when we got our Signature Xs and maybe met at the intro in Fremont in ‘15.
I never got any explanation from the Service Center. Just complete RDU replacement inter the powertrain warranty. That you had a similar problem makes me wonder if it was a design flaw affecting low VIN Xs.
With this failure, and the collapse of the left front suspension due to a fracture of a linkage (an issue the NTSB is tracking), I decided to trade in my signature and get a new long range X. Sometime in April. Hopefully it will be free of some of the low VIN failures many of us have experienced. No regrets, because it’s been a joy to drive.
 

vangogh

Member
Sep 4, 2015
371
199
Sunnyvale, Ca
Thanks vangogh. I think we corresponded in ‘16 when we got our Signature Xs and maybe met at the intro in Fremont in ‘15.
I never got any explanation from the Service Center. Just complete RDU replacement inter the powertrain warranty. That you had a similar problem makes me wonder if it was a design flaw affecting low VIN Xs.
With this failure, and the collapse of the left front suspension due to a fracture of a linkage (an issue the NTSB is tracking), I decided to trade in my signature and get a new long range X. Sometime in April. Hopefully it will be free of some of the low VIN failures many of us have experienced. No regrets, because it’s been a joy to drive.
I am now thinking of a trade in option when my extended warranty is close to expiring. I was really hoping that a fully autonomous (no steering wheel) capable car would be available before trade in but that is looking like wishful thinking....
 
I have a 2017 100D X which I took into SC for work on the axle due to issues when I accelerate. While there they discovered a “leak” in the front Drive unit. I hadn‘t gotten any error notices. The SC said they happened to have a unit on site and could replace right away. I was told that “all drive units are OEM remanufacutred and fully tested But the half shaft is new”. Opinions on getting a refurbished unit? Shouldn’t the replacement be new? I have an extended warranty that expires in 2025 or 45,000 more miles which ever comes first. TIA
 
Check the warranty to see if Tesla can replace your FDU with remanufactured parts at their discretion. If so, you may not have a choice.

I’d like to believe that a remanufactured unit is as good as new if all parts having damage or wear are replaced and the unit is tested to original specs. It all depends on the quality control processes at the remanufacturer.

Of course, these are expensive vehicles and we like to think that all the parts are of the highest quality. Unless others have had bad experiences, I’d be content that I got a perfectly good replacement part.
 

vangogh

Member
Sep 4, 2015
371
199
Sunnyvale, Ca
Got my X back with a new rear drive unit. They just said it was a failure of "communication between the RDU and the HV battery". Don't know exactly what that means, but the new drive unit is working well....Unfortunately, they did not look at the clicking noise I'm hearing during acceleration (started at around 45k miles and has gotten progressively worse - at 65kmiles). (see video). Seems like it may be an issue with the LH Front Drive Unit Clevis Mount and Both Front Halfshafts (apparently there is a service bulletin out on this). Now I have another appointment later this week...

 
The RDU problem might be different than mine. An internal short was suspected. What bugs me is that an RDU failure disables the car.

I had the same front end noise issues at maybe 20K miles. Both halfshafts were replaced with upgraded units. I also noticed that there was more noise when they were cold.
 

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