i30 Gear Shift Indicator Failure

Sounds nasty! Does the error code refer to any specific part of the transmission, like a solenoid or sensor? An incorrect signal from a sensor (perhaps the gear selector position sensor) could explain the display issue AND the weird shifting behavior. That sensor provides data to the Transmission Control Module (TCM). If the TCM gets bogus data, it might think you're in a different gear than you actually are. Check the wiring and connections to the transmission control module, too.

Thanks for the quick reply! You mentioned the gear selector position sensor. Is that a common failure point? And is the TCM relatively easy to access on the i30, or am I looking at a major disassembly job?

While not 'super common', the gear selector position sensor does fail sometimes, especially with age and mileage. A defective control unit may also cause the described issues. The TCM's location varies, but it's often under the dash or under a seat. If you're getting those symptoms (especially the grinding), I'd seriously consider a workshop. They'll have the right diagnostic tools to pinpoint if it's the sensor, the TCM, or something else entirely. Ignoring it could cause catastrophic gearbox damage! Cost of repair will be around 1000€.

Appreciate the advice. I suspected it was beyond my DIY capabilities. I've booked it into a workshop; they've confirmed it's a defective control unit. Thanks again for pointing me in the right direction!