Thanks for getting the code, we have seen this numerous times on the forum, it is P1A15. There are no trouble codes that start with a "T", but they sound the same. Here are troubleshooting notes for this code taken from the Factory Service Manual, which calls the MCU the EMCU.
P1A15 is High-Voltage System Error #1
Description of how the system operates:
The high-voltage circuit activation and shutdown are controlled by the EV-ECU. The EV-ECU also monitors the voltage of the smoothing condenser [a big black capacitor] in the EMCU via the CAN communication.
How does this code get set?
If the charging time of the smoothing condenser in the EMCU exceeds a specified time, the diagnosis code No. P1A15 will be set. That is to say, if it is taking too long for the capacitor to charge up to the full level, which is equal to the voltage of the pack. Or if the measurement value reported by the sensing circuit indicates that the the capacitor voltage is taking too long, then it will throw this code.
Probable Causes in the service manual include:
1. Damaged wiring harness or connector(s)
2. Malfunction of the high-voltage fuse No.1 (Main, 280A) (inside the main battery assembly, accessible)
3. Malfunction of the main battery assembly (possibly damaged contacts of main relays, aka contactors)
4. Malfunction of the EMCU
As you can see they don't list a 5th cause, a weak, old or worn out 12V battery, but we have seen that code appear due to 12V battery issues. That is why i recommend to check and verify the 12V first to rule it out.
There are several threads about the P1A15 code that go into technical detail about repairing the circuit board or replacing the MCU with a salvaged unit for much le$$. You can find those by searching "P1A15" if you are interested and have time to read.
Since your car runs and drives with the code cleared, then it means your MCU is not permanently damaged--electronics don't heal themselves when broken. But it could have some degraded components, especially since you mentioned that high ambient temperatures were involved. One member had this code occur and found it was related to temperature.
That code does not permanently disable starting the car, if you re-try to start after removing the key and the capacitor value reaches the expected value, then the car will go to READY and the HV (!) light will go out.
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