Hello i'm a new member and toyota owner.My question is I have a 97 4 runner,with a 3.4 v6 and i'm getting a code p0136 sensor circuit malf. bank 1 sensor 2,downstream heated o2 sensor circuit "low voltage". The truck doesnt seem to run any different and when i erase the codes it didnt repeat for about 3 weeks.I need to know if anyone has had this problem, and did replacing the sensor cure the problem.The two times i got the check eng light it was pretty cold and within the first 5 minutes of running.Also if i do replace it should i stick with yota sensor or are aftermarkets ok.Thanx in advanced for your help,and this a great site,you've already been a big help in my rear axle seal and bearing change.

 

That trouble code gives me P0136 O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)
So this means the O2 sensor behind the converter is bad and needs to be replaced.
I would use an OEM Toyota sensor (get them for $80 from TOR, member on Yotatech).
...or you can get them from http://www.sparkplugs.com (at the top menu).

A new sensor will definately stop that CEL (I had the same thing happen on mine)!

 

thanks for the help,just wanted to be sure the sensor would fix it.just called my buddy ,who is a parts guy at a local yota dealer "sweet ".Thanx again for the help.