I purchased my 2004 Discovery II about a month ago. Had no issues during that entire time. Then today after I had driven about 15 miles in the city (engine up to full operating temp) I parked the car outside with the ambient temperature about 15 degrees (gotta love Minnesota).
After about 2 hours I came back out and started and took almost immediately. within 100 feet or so the SES light came on.
Read the codes out when I got home and found two codes: P1412 and P1417. This indicated something was not right with the secondary air injection system, so a vacuum line hunting I went....
The solution was a piece of cake. The tube leaving the air pump was simply not connected to what, for lack of proper definition (feel free to jump here and tell me the technical term), ill call an air injection manifold. see pictures.
The line was tucked behind beside the pump so it was not terribly obvious it was not supposed to be there. Had I not been such a newbie to land rovers I would have seen this. Once the line was reconnected and the codes where cleared all was right as rain.
My theory stands that just before I bought the vehicle the service records indicate the plugs and wires had been changed and for better access the mechanic had removed this line to install them and just never put it back.
I am surprised that I was able to go so long without throwing a code with this not being right. oh well.