On my way home from work today my gti seems to have developed a fault. It's now not firing on all cylinders and when scanned showed the error message ' 00768 Rear Heater Core Temp Sensor (G154)' any ideas? Looking on Google it would seem to be coil pack problem but one guy had this and it was a melted piston! Its under warranty but would it be safe to drive back the 20 miles to the garage i got it from?