Alert DI_w115: Drive unit internal temperature imbalance detected

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Well-known member
Supporting Member
Aug 7, 2017
Oak Harbor, Wash.
Leading with this: as of this writing, no, I don't know how to properly fix the problem associated with this Alert. You Tesla owners who find this by Googling, the below may not even apply to your Model S. I'm putting this tale out in public to provide data for others do find, but I'm not claiming it's useful.


I've eliminated rotor liquid cooling on my LDU and had this Alert come up during the first test drive. And, now it's gone. Let me explain . . .

My driveway is sloped to the garage, and the car is parked nose downhill. I partially installed the LDU including mounting it in the chassis, connecting coolant hoses & all electrical, filling with coolant, reconnecting 12v & HV. No axles installed, ball joints disconnected, etc. No brakes.

I ran the TPD 1.1.42 "Coolant Air Purge" for the prescribed 32 minutes, refilling the reservoir as needed. Turned on the car, shifted to Drive, and the axle receivers spun at "creep" speed, and no crazy noises were heard. Good time to stop, as it had been a looong day.

I completed the LDU install (axles, etc.), and drove it late in the day. Within three miles:


Ambient temperature was 55°F: cool-ish for here.

I drove another three miles home, did not turn off the car, connected the laptop and saw this (to be clear: this is a later screenshot, which is why you see multiple Alert instances):


Notice: the IC is complaining about battery temperature, but the current Alert is Drive Unit temp imbalance. That's not confusing at all!

I asked @hokiematt for a TPD screenshot of inverter temps for a non-modified LDU, and he sent this:
. . . which are pretty close to what I see on my screenshot above (taken when I could obtain the widest ΔT readings).

Back at home, I parked the car nose uphill, re-ran the Coolant Air Purge procedure, and the reservoir level didn't drop. At all.

The car sat undisturbed Thursday.

Switching to TPD 1.1.46 now, I attempted to use the Pump Tool (which was ineffective), walking front to back several times, feeling/listening to the pumps . . . and then I saw the reservoir: completely EMPTY. IDK whether it emptied over the course of the two days it sat, or when I was trying to work with the Pump Tool.

I refilled it, then played with the Pump Tool more, gave up and decided to go for a drive. I got in the car and was about to shift to Drive, but I then heard gurgling -- a noise I've heard before. I got out and checked the reservoir again: half-empty.

Refilled, drove 20 miles: no warnings about hot battery.

Got home, parked nose uphill, checked reservoir: lower, but not half empty. Topped up again.

For the moment, and until I can put more miles on it, I'm calling this "fixed". I have theories about the DI_w115, but they're just semi-educated guesses.

Reference to alflash's vid on the same Alert on another RAV4 EV.

I don't like to jump to second-guessing engineers' documentation . . . but this has the feel of a mismatch in software (for the RAV4 EV).
Based on the story you told, it's pretty clear that the coolant lines were not purged properly and that led to some thermal abnormalities. However, it's not clear from your story whether you touched the battery coolant loop or just the big one that includes the DU and charger. Clearly the dashboard warning message was being applied to all thermal events even though it clearly says "battery".

My theory is that there were bubbles moving through the inverter which intermittently overheated. The temp reading you saw is likely not the peak temp that was seen by the sensors.
The battery and powertrain loops share the radiator as a common, I think, so introducing air into the powertrain loop could also affect the battery loop.

I have theories, but not worth exploring. I did the "Toyota way" this time; next time, I'll use my vacuum purge setup, as I have for all my other cars for around 30 years. But I wanted to give the "Toyota way" a chance, because I also want to duplicate problems that other people may have in future, and have this info publicly available.

IDK why Toyota would implement a catch-all thermal event IC message that names a specific part of the drivetrain; that looks like an oversight/bad coding, rather than an intentional catch-all message.

I was watching TPD like a hawk on runs 2 & 3, and it updates frequently, so I'm doubting a "didn't see it" inverter temp spike, but without freeze-frame data, [shrug].

Someone will come across this via a Google search and possibly have more data to work with that I did.
Once when I was working with a friend to replace his failed RAV4 EV coolant recirc pump (the one that you can see and reach with the hood up, near the radiator) it was whining and not circulating coolant upon initial installation.

It turned out that there was an air bubble next to the pump and the pump was spinning uselessly in air. I loosened the clamp on one side to let the air out. The pump caught fluid immediately and began to recirculate it. My son had a similar problem on his mid 1990s Honda Civic ICE vehicle and the procedure was to “burp” the coolant line.

I wonder if you encountered some similar phenomenon where the coolant purge was prevented by some poorly located air right by a pump.

Someone will come across this via a Google search and possibly have more data to work with that I did.
A Google search* suggested a link to my video, which shows the short-term appearance of this code while RAV4EV is moving.
In this case, the inverter temperature = 40°C (104°F) and the stator temperature = 64°C (147°F).
Notes The coolant level in the vehicle is normal and the Coolant Air Purge** procedure has been performed.


**For example,
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