Cat efficiency bank 1&2 and 02 Sensor 1 & 2 error codes
 

2002 X5 3.0 140k miles got error codes for

stealer is saying need to replace everything for about 3k. did some reading and not sure about changing cat yet (no odor, no noise). The dealer proposes changing all 4 O2 sensors first. I ordered all 4 sensors and the tool and will try to tackle the project myself. I searched but was unable to find pictures on the replacement - is there a DIY with detailed instructions? thanks in advance

Crawl under your truck and you will see all four o2 sensors, two before and two after the catalytic converter. I searched the same DIY, but they are just too easy to locate.

Might be easy to locate, but not the easiest to change.

$3000 for all is not too bad - I paid $2200 just to replace the cats a year or so ago at an indy mechanic.

I'm just changing the sensors right now and I have read conflicting messages on how easy they are to replace. I guess I'll find out shortly. If I cant get it, I'll take it to a local mechanic that used to work at BMW.

Please if anyone else has any pictures or more input on changing the O2 sensors, please post. thanks

Seriously all you need is an open wrench (not sure what size, maybe 22mm not very common, alternatively 7/8") or a special o2 sensor socket (you may not have enough room because it is tall). I changed o2 sensors on my e39 and e46, which was more difficult coz you don't have much room to play. X5 is relatively easier and it indeed is a very easy DIY.

What codes are you getting? Catalyst inefficiency bank 1 or 2? I replaced both pre cat O2's at 110k. Took all of 30 minutes. Bought the claw foot O2 tool from Napa, bought the oem bosch O2's from Napa #13477 about $67, don't bother with post cat O2's unless you are getting fault codes for them, they are only sniffers...
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I'm getting error codes for both banks 1 and 2.

update, the front o2 sensors on the 2002 x5 3.0 are on the topside by the valve cover (on the left if you are facing the engine - passenger side). the job was very easy though space was tight. i suggest getting the sensor tool to help, also may want to unbolt the washer fluid reservoir to get more room. front done, disconnected battery for now to reset the SES light. The bottom are tough to get at without putting the car on ramps. will leave for another day.

And the downstreams sensors are the ones that monitor the cats, so if it is cat converter efficiency faults it could be those. I've seen weird things throw the cat efficiency faults, it came up in my mothers E39 when I fixed the secondary air system and it put more air in at cold starts... cleared it and it never came back.

im not a tech but it sounds like the dealer is throwing parts and your money at a problem they can't figure out. i'd be looking for another opinion.