Just had the car off the road for a week, jacked up at the front (and battery unconnected). Just before I jacked it up, the fuel light had been on for about 20-30 miles. Anyhoo car's back on the road today and despite putting in £10 worth of diesel the fuel guage is still where it was and the fuel light still on. Any ideas please? Just wondering if I need to fill the tank to perhaps somehow free up the guage?