Service engine soon light

I recently installed a block heater in my 2002 Lancer. It took a while due to the location of the freeze plug. I had to take off the exhaust manifold just to get to the freeze plug. I got it all done and the engine seems to be running fine. However, the SES light came on. I tried the disconnecting the neg terminal of the battery to reset the computer system and waited 15 minutes. I also turned the car on and let it run in idle for 15 more. There was no light but when I turned the car off and then back on the light came back on. The nearest dealer is a long ways away (297 miles). Is there a way I could fix it myself or do I need to send it to somebody to do a diagnostics?

Went and got a free diagnostics and the P0135 code came up. The guys there think it has nothing to do with the block heater but it is possible it is reading a high level of oxygen. The code is the O2 sensor Heater Circuit Malfunction Bank 1 Sensor 1. I am not sure if the sensor itself is busted or if it is from the O2 reading. Any suggestions?