CEL Turned off now I have Knock Senor Code...
 

I've had my CEL on for almost a year (havn't driven it everyday tho) since I installed my Testpipes (96' TT 2nd set of o2 sensors installed into bungs in testpipes) code P0141 O2 Heater Circuit (Bank 1, Sensor 2)

Today I was driving to work and I noticed an orange light dissapear behind my hand sure enough my CEL turned off. I turned on and off the car a few times and it didn't come on. So I checked my ECU for codes and pulled PO325 Hock Sensor 1 Circuit (Bank 1)

I'm confused why my o2 code would dissapear aswell as my CEL light and now this code is stored in my ECU? I cleared it to see if it would bring back my old code and the light and it didn't the Knock Sensor code came back...

Any ideas?

Tim