I was attempting to improve my cold starts and ran into an issue with the ECU that required re-flashing the firmware.
I started with the ECU connected to my laptop, and it remained connected until after the issue occurred. I started the car. It started to die, so I shut it off then made some adjustments to the CLT multiplier. I did the same thing a couple more times. While trying to start again, the car would not start. I couldn’t hear the fuel pump prime and it didn’t sound like it was firing while cranking. I also lost connection to the ECU from my laptop.
I checked for the ECU in the device manager and did not see it even after disconnecting and reconnecting to the laptop. I removed the cover to inspect the status LEDs and all four LEDs next to the STM were lit up solid. I attempted to get the ECU into DFU by using the boot and reset buttons. The LEDs next to the STM remained off while doing this, but still no device was found in the device manager.
I removed the ECU from the car and went to my PC. I attempted to connect it to my PC using both the same USB cable I had originally used and a second one with no success at first. I could not see the ECU in either the device manager or the STM programmer. I tried probably 10+ more times booting into DFU using the reset button, holding boot while plugging in the USB, alternating cables. After going back to the original cable, holding the boot button, plugging the cable in and making sure the connections were firmly seated, it finally showed up as STM32 Bootloader in the device manager.
I was able to connect to it with the STM32 Programmer, and flash the latest firmware build. After disconnecting and reconnecting the USB the LEDs started behaving as expected (Yellow solid, blue flashing, others off) and I was able to connect to the ECU with TunerStudio again.
So it turns out my USB connection isn't great, possibly due to the cable, so that likely contributed to not seeing the board in DFU during some of those initial attempts.