brasil

I finally picked up an OBDII scanner a couple of months ago after the CEL came on, and that revealed some codes that relate to one of the O2 sensors and sensor heater, but after much searching of the forum, google, and reading Marcus' DIY page about the topic (http://www.marcusfitzhugh.com/CLK/DIY/o2sensor.html) I was still left with questions, the main one being:

How do I map the OBDII terminology of banks and sensors ("bank 1 sensor 2" in this case) to the actual correct part I need to purchase to replace it? I was looking at Bosch O2 sensors, and depending on which sensor it is the wires may be of different lengths, and other obscure (to me) factors may be different. Unfortunately, this info about Bosch "Universal" Sensors went right over my head: http://www.marcusfitzhugh.com/CLK/DIY/o2univ.html.

There are four O2 sensors in the W208, two upstream and two downstream, right?

After clearing the codes and driving again, here's what I know:

- "P0141, Oxygen Sensor Heater Circuit Bank 1 Sensor 2" appears as a PENDING code immediately, and may or may not reach the CONFIRMED stage

- within less than 100 miles of driving, "P0136, Oxygen Sensor Circuit Bank 1 Sensor 2 (See P2270, P2271)" appears as PENDING, and not long after turns to CONFIRMED

The CEL does not turn on at this point, and I'm starting to think it only turned on after I filled up at a gas station that may be peddling crappy gas (CEL light has come on both times I filled up at this particular station).

My car just hit 94,000 miles and looking through the records it appears that the O2 sensors have never been replaced. As I'm on a really tight budget right now my goal is to fully diagnose the problem, buy the parts myself, and have my local shop here in "Da Bronx" just do the install. What's the next step on this? I'm stuck.

dlbehrns

I think bank one is the drivers side and sensor 2 would be the after cat or second sensor. Perhaps someone can confirm that. These guys are pretty reasonable http://www.autohausaz.com/search/pro...ar=1999&cid=o2 sensor@o2 sensor&gid=5132@Oxygen Sensor

rsparso

I believe that ID is correct, bank 1 drivers side, 2 downstream sensor. Certainly the downstream sensor, so try the drivers side and if that's not it the passenger side would seem a good bet.

brasil

Thanks for the replies, guys. What you're both saying makes a ton of sense, which boils down to the following:

bank 1 = driver's side
bank 2 = passenger side
sensor 1 = pre-cat (upstream)
sensor 2 = post-cat (downstream)

I hope this info helps others as well. I'll post a follow-up after i get this repaired with additional info/confirmation.

Jim_p

You can always unplug one of the sensors and see what code is set. Usually both upstreams are the same and both downstreams are the same. At 100K miles they should all really be changed anyway.

-Jim