'03 Tacoma 4x4 4-cyl 108k

My truck just set the P0135 code. This is a an 02 sensor code for bank1/sensor1.

I checked an on-line FSM and found that it's the O2 sensor just downstream of the exhaust manifold, upstream of the cat.

I reset the code and it returned after a couple of short trips.

Questions:
1. Besides a bad 02 sensor, are there any other known causes for this code?
2. How harmful is it to drive the truck for a few hundred miles with the code set?

 

Have been told truck will run lean, and can be driven. but dont drive it like you stole it.

If you put off replacing sensor and it can damage cat and even rear sensor.

Use OEM replacement

 

Hmm. I would think it would run rich. Running rich seems like it would be reason that the cat and 2nd sensor would be damaged over time.

I have found that Denso is the OE supplier. They also sell sensors that appear to be "right". The part numbers I have found are 234-9001 and 234-9002, the only difference being the length of the harness. Does anyone know if these are the same as the sensors Toyota buys from Denso?