I have a "new" 04 Discovery that has (had?) a P0455 code (large leak evap emissions). First thing I checked was the gas cap, and indeed the cap was loose. My first question is what is required to reset the code (x number of restarts W/O fault, X elapsed time W/O fault, manual reset, other)?

Second question is why is that code not mentioned in the Service Manual?

Rod
55 MGTF
67 Jag EType OTS
00 Disco
04 Disco

 

I suspect using your code scanner to reset will be required other than brute force battery disconnect, which gets other codes that may be lurking. Some parts stores won't do clear codes anymore, but some loan/rent the code reader and you can DIY. If wanting to have your own the Ultra Gauge at $70 is worth a look, it reads and resets codes, and displays live data like accurate coolant temp.

Here are some pages from the Rover/Bosch ECU manual, which cover that code. The whole ECU manual can be had in sections in my signature.

 

Or, you might leave it alone for awhile cause if I remember right, it may reset itself for that particular code. If not got to use a scanner and do not try to get rid of it by disconnecting the battery, as Buzz mentioned it will just cause you to possibly throw other codes and or loose some of your adaptive memory.

 

i got tired of waiting for the Service Engine light to go out so
i tried disconnecting the battery, which did reset the light. I was not worried about possible problems from disconnecting the battery as
i do it frequently when towing behind a motorhome.

Rod