i have 03 taco x cab 2.7L truck. i got a code PO136 O2 sensor circut malfunction 1/2. would this be the sensor before cat or after?

second issue with my headlights on i turn on left turn signal and the rear blinker,back up light,tail and brakelight all blink only when head lights are on and only that side. i swapped the blinker bulb with the rightside and still no change.

any idea's on what is causing this?

 

i fixed the light issue the culprit was a bad ground, still looking for the answer for the o2 sensor though

 

1/2
bank one/sensor 2 thanx for your help