Hi:

Looks like age or the East Coast heat wave this week finally did-in the sensors on my RX.

Several days ago, after driving about 20 minutes after a cold start, the VSC & CEL lights came on on my '02 RX. After checking this forum (Always thankful for the knowledge here!), I reset the lights by pulling the fuse, drove some more the next day and the lights came back. Went to Auto Zone and received a readout with the following two codes:

PO136 - Heated O2 sensor - bank 1 sensor 2 (HO2S12) circuit malfunction

PO171 - System too lean - bank 1 (Cylinder number 1 denotes bank 1)

NOTE: There is no noticable change on the vehicles performance...seems to be operating normally.

From poking around previous postings here, it seems that one or more sensors may have failed. Question:

Is this problem caused by just one of three sensors that go in the exhaust path (pre-cat front, pre-cat rear or post cat)...OR...is this something else? Some members seem to indicate that replacing the sensors in the exhaust path after the engine fix the VSC/CEL problem.

Thanks for all replies. DIY work is no problem for me. Have done plenty on my car..again...thanks to this forum and have saved a ton of $$$$.

Tom-

 

Given that you don't have one of the codes for the two up front a/f sensors, this remains to be seen. The PO136 is code is an after cat (main cat below vehicle) and doesn't affect the air/fuel ratio matrix. This could have been some bad gas or other issue. I'd actually have to stick in my laptop with diagnostic software and see what kind of fuel trim readings along with the voltages on the two up front a/f sensors to see what would be going on here to trigger this. Some more advanced diagnostic software (not sure if the Autozone scanner would do this), have a freezeframe that shows the numbers at the time the CEL was triggered. I use this frequently to track down issues in my own RX. You could have some clogged injectors on that rear bank, but again I'd have to see the readings on the sensors to lock it down.