CEL Code, tag expired need help!!

[HIgH_ScHoOL]

So I have a 2003 WRX, it has full turbo back exhaust and it obviously causes the cel to come on. I bought the helix cel fix and wired it up, light went off and the car passed emissions, about a week later the light came back on. I reset the computer light stayed off for a good while. Now its time to get emissions again and the light is on again. Im not sure what it is this time, the light will not stay off, after the reset it comes back on with in 40 miles or so.

I got it scanned, the code reads:

P0546
Exhaust Gas Temp.
Sensor Circuit High
(Bank 1 Sensor 1)

Any help would be great!

[Z U L8R]

not sure if your car has a seperate exhaust temp sensor and 2 oxygen sensors, one before (sensor 1) and one after (sensor 2) the catalytic converter.

if it does then i'd start by testing/replacing the solo temp sensor. if it's built into the oxygen sensor, then you need the pre-cat/upstream oxygen sensor which will be the o2 sensor that is BEFORE the catalytic converter.
gl =]