Service engine light came on the other day, had it scanned at the local parts store, P0156, bank2 sensor2.
OK, so I buy one (Bosch) and replace it, cleared the code. Driving home from friends garage I stopped to eat, upon leaving the SES light was on again and sure enough, same code, same sensor. WTF?!?!?! Darn thing shouldn't have gone bad in under 20 miles (but I suppose anything is possible).
Two questions, is this something that happens on these vehicles where the problem is something OTHER then the O2????
Or............<insert suspenseful music here> did we swap out the wrong sensor? The printout from AutoZones website as you can see below is rather generic looking(also looks like a transverse mounted engine) shows bank1 as drivers side, sensor1 is in the manifold and bank1 sensor2 is AFTER the Y pipe junction. On the passenger side it shows bank2 sensor1 also in the manifold but the next one downstream is the previously mentioned bank1 sensor2 and the next one (after the cat) is bank1 sensor3.
The one I replaced was passenger side right after the manifold to downpipe flange, with the doghouse off it was right there basically next to the bellhousing close to a passengers left heal. Got my fingers crossed that diagram is wrong and bank 2 is the drivers side. Did a quick search and found many diagrams, some as crappy as this one, MOST show (for Fords) bank 2 as drivers side. <fingers crossed>
TIA

 

Bank 2 is indeed the drivers side.

I'd NOT trust those parts stores cats advising replacement of a sensor based only upon a DTC----its just as common for a sensor to throw a code based upon other circumstances than the part itself failing. For example the Actron Code Lookup site shows this info about your DTC: P0156 Oxygen Sensor Circuit Bank 2 Sensor 2. There's not much to say the sensor has failed---it simply says its conditions are outside of its acceptable operating range, further diagnosis is in order.

Not sure what to advise about making repairs or tracking down your DTC but be careful of parts sellers who know nothing about repairing vehicles.

 

Bank 1 is passenger
Bank 2 driver side
Bank 1 sensor 1 is before cat
Bank 1 sensor 2 is after cat
Bank 2 sensor 1 is before cat
Bank 2 sensor 2 is after cat

And yes you installed the O2 sensor on the wrong side.
I've seen critters chew on them wires so give a good visual.

 

Thanks. We looked up and found the error of that diagram and swapped out the correct sensor. SES light was off for two days and popped back on again this afternoon. Same exact code. F&#$%!*@k

JWA, you mentioned some other issue could cause the sensor to read bad...what possibly could cause that without throwing codes on other O2 sensors or throwing other components codes?

 

The sensor is bad---IIRC Bosch is not advised for Ford applications---or some issue within the intake/exhaust system is creating a condition that will cause the sensor to send the DTC. Unfortunately I'm not that familiar with the O2 sensors and their proper operation so can't be more specific. I do know an advanced level scanner will read each sensor while its operating and can then extrapolate what might be the root cause of the DTC.

FWIW a friends '06 E350 w/5.4 suddenly developed a huge reduction in MPG's and it tracked back to a single O2 sensor. We replaced all 4 as the others were on the thresh hold of triggering DTC's so he opted to spend the money---Motorcraft BTW---to increase reliability. If you go that route get the correct Motorcraft part number from RockAuto and go shopping online--we needed ours in a rush so had them next day through the dealer. Without a doubt better prices can be found with a bit of looking around.

Good luck with this and sorry I can't be more specific or helpful.