From Ross-Tech Wiki
17911/P1503 - Load signal from Alternator Term. DF: Range/Performance / Implausible Signal
- Alternator faulty
- Voltage Regulator faulty
- Wiring and/or connections faulty
- Check / Replace Alternator
- Check / Replace Voltage Regulator
- Check wiring and connections
- Check the fuse box that is in the battery tray, it might be burnt, the fuse or the complete plastic box (pretty common failure on Sharan because it carries so much electrical load). If so, change the complete fuse box, it is not too expensive fix if this is the cause.
- When found on the BEW engine, check MVB 16, Field 1. In most cases values will be between 15% to 30% at idle. 0% could indicate a failed or incorrect alternator.