Aygo transmission fault

Whoa, that sounds rough! Grinding noises are never good. I had something similar happen on my old Fiesta, though not a Toyota. Before you panic about the sensor, have you checked the gearbox oil level? Low oil can cause all sorts of mayhem with shifting and pressure, and might trigger the sensor.

Thanks for the suggestion. I hadn't considered the gearbox oil level. Could a low oil level really cause all those symptoms, including both engine and transmission warning lights and a stored error code for the pressure sensor?

Absolutely! A low oil level will cause the sensor to throw a code because it's not getting the correct pressure reading. The lights are just a general 'something's wrong' warning. I'd bet money that topping off the oil (or getting it done professionally) will solve most of those problems. If that doesn't fix it, then yeah, it might be the sensor itself. But rule out the simple stuff first. Although, with grinding noises, it might be best to take it to a workshop right away, so they can take a look at it.

I appreciate the advice. As you suspected, the gearbox oil level was critically low. A top-up wasn't enough because it had been running with insufficient lubrication for too long. The oil and filter were replaced, and the pressure sensor was replaced too. Total repair cost was 365€. The car is now running like new.