I have an 03 Discovery HSE that has had a rough idle for a week. Now it is getting much worse and the check engine light came on. I ran the diagnostic and have the above codes showing a misfire in number 4 cylinder and also a high voltage detection in the bank 1 02 sensor 1.

I would love any suggestions on where to start.

Thanks.

 

Use
http://enginecodemaster.com

You have a short in your O2 sensor.
+12 heater wire is hitting the sensor input wire.
Replace the sensor.
Look for burned wiring.

Your #4 cylinder is misfiring.
Change the plug.
Change the wire to the plug.
the boot on the plug is probably cracked or melted.

Worst case - you may have a valve sticking - but I doubt it.

Summary:
change O2 sensor - get one from Amazon.
Change spark plug.
Change spark plug wire.
Everyone says use 8MM wire.