Sonic Transmission Oil Pressure Sensor Fault

I've experienced something similar with my Sonic, though I can't recall the exact mileage. The transmission oil pressure sensor can be quite sensitive. A drop in oil level, even a slight one, can trigger the sensor and throw the system into limp mode to protect itself. Have you checked the transmission fluid level recently? If it's low, that's definitely the first thing to address. Be sure to use the correct type of fluid as specified in your owner's manual; using the wrong fluid can cause all sorts of problems with modern transmissions.

Regarding the transmission fluid level, what specific symptoms did you have? Were they like the grinding noises I've described? Was the fault directly from the low oil level, or were there other factors, like sensor malfunction?

The grinding noises weren't as pronounced in my case, but the slipping and unclean shifts were definitely there. And yes, after topping off the transmission fluid to the correct level, the issues disappeared, and the error codes cleared after a reset. However, given the grinding noises you're experiencing, I'd strongly recommend having a qualified technician inspect the transmission. It's possible that the low oil level caused some damage, and it's best to catch any potential problems early on.

Following your advice, I went to a service center. They found a transmission oil pressure sensor fault from low gearbox oil. Replenishing the oil and replacing the sensor cost 365€. Your guidance helped speed up the diagnosis and prevent worse problems. Thanks!