2012 Seat Ibiza 5DR 1.2 TDI CR REF SE 4 4DR

Brand new front tyres
Brakes done in march, all still really good
Serviced every 10xxx-15xxx kms
Test out Aug - booked and paid for already for new owner, should fly through
Tax 09/25 - cheap tax € ... 190 for the year

Check engine light on dash, confirmed this is for exhaust gas temperature sensor, changed the sensor and cleared the code but the light stays consistent, nothing is actually wrong just needs a better diagnostic tool to clear the code.