A quick google suggests a potential issue with brake fluid (but this was checked by a garage not long ago) or the sensor. Are there any checks and fixes a *complete* n00b like me would be able to do without any tools?

The issue first started when the parking brake was tightened a while ago, but got much worse since yesterday, after a stuck rear brake caliper was fixed and pads replaced. It seems that messing with the braking system has upset my old boy somehow
