SES light has been on for quite some time. It first only had the O2 sensor code to which i replaced the front O2 sensor. The SES light never went off and has been on for about 1 yr or so. The other day i was driving on the interstate and the SES light started blinking at me. So i went back and had the codes read again and i have 2 codes stored: P0131 & P0137, which show Heated O2 sensor bank 1 and 2. Do i need to change out both O2 sensors or does someone know another reason why these errors display? Any input would be greatly appreciated.