2000 TDI Check Eng Light ON

I have changed all four glow plugs and the relay. The light continues to come on and stay on about 20 seconds after cranking. Fuel mileage has dropped off about ten to fifteen percent. I believe the tech told me the code he gets is P080 or P030. Any suggestions?

the harness is a common failure on theese. They get loose from engine vibrations over time and cause "sporadic" glow plug faults. there about 40.00 or so new and you have to cut and butt connect the new harness on ,making sure you dont reverse the leads when you cut them. If you have a 4 wire glow plug harness theres no cutting just need to remove the battery and harness cover on the shock tower and it plugs in (and its more$$$)

Thanks for the idea!!! I was thinking along those lines too.