The internet is truly amazing. I just had the exact same problem with my 2003 montero limited. I brought this one to the dealer because of a service engine soon light being on and they came up with:

po155 b2s1 sensor --Bad heater circuit (according to invoice for diagnostics)


I paid $115.50 just for the code and they want $310.15 for the part and and they want another $84 to put the sensor in after they get it in (they did not have the part on hand)


If you could, let me know how your DIY replacement goes and I might just go down the same road and save $$

I PM'd you my email.

 

I don't think PM is working- Drop me a line - jshanerobinson@verizon.net- The part was $215, and I won't get it until 12-27. Should get it in by the 4th or 5th of Jan.

 

I've got an '03 with the same code that just came up yesterday. Went to autozone and they pulled the code for me. I've got 55,000 miles with an extended warrenty from the dealer. Isn't this part supposed to be covered under the powertrain warrenty? Emissions control falls under the warrenty doesn't it? I'm going to take the car back to the dealer and see if they'll fix it under warrenty or the extended warrenty.
First post by the way.

Jae

 

At first thought I would say that it isn't covered, although it doesn't hurt to ask...especially if you just got it. I have an extended warranty on my MS(through a third party, not the dealer) and it doesn't indicate 02 sensors in the contract so I haven't tried.

The 02 sensor is a "maintenance item" like brake pads so you may be SOL.

Oh, and Welcome to the forums!

 

Just got back from the dealer. The O2 sensor was covered under my extended warrenty. They picked up close to 400, and I paid my 100 deductible. This is the first time I used the extended warrenty, not a bad experience. The dealer had to call them to see if the part was covered.

Jae

 

Got it done today- first thing is to disconnect the battery, then disconnect the 02 sensor where it plugs in up top under the hood, right near the oil and tranny dipsticks. If you don't unplug the sensor before you start loosening the nut underneath, the wire will get all bound up from turning, and you won't be able to get the nut loose enough to take it out of the exhaust. Don't ask how I know.


Go underneath, get your 7/8 or 22 MM wrench and have at it. It is on the drivers side- if you're underneath the truck, and you look at the exhaust as it comes off the motor, it is the one furthest up. The two closest to you plug in underneath the truck, so you'll know they aren't the ones you need.

http://www.flickr.com/photos/4063657...7603677478985/

You'll likely have to keep the battery disconnected for a couple hours so the Check engine light will reset.

I got the Sensor from http://www.autopartswarehouse.com/
Part Number: BS15599. (Bosch).

Old sensor was a Denso.

 

Thanks for posting the replacement information/pics! I am going to try to have my 02 sensor fixed under warranty like hawkgt since I am covered for another 4k+ miles, but it is nice to know that the process isn't totally crazy.

One question, you didn't say anthing about a special 02 sensor socket...I am guessing that the open-ended wrench did the trick?

 

Yep- Theres plenty of room for a wrench in there.

Regarding the other two sensors underneath the truck, I guess they will be sensor #s 2and 3. I'm wondering though if they'll both show up as Bank 2, as one of them is right in the middle of the engine.......maybe since it plugs in on the drivers side it'll be bank 2.

 

Thanks for posting this. I got the warning around the same time and the code pulled at my local autoshop was P0155 02 Heater B2S1. Checked with Dealer and it is not under warranty anymore (3 yr./36K http://www.mitsucars.com/media/owner...ry_booklet.pdf) The dealer wanted $400/450 plus labor to replace it. Also said they couldn't guarantee that would be the problem without seeing it themselves. I think I'm going to have a try at fixing it myself so the advice is helpful!


Seems to me that there is a bit of a chronic problem with these in the Monteros after a little web searching.

 

I think the problem is more with the Denso Sensors, I expect to get more out of the Bosch.

It took me all of 45 minutes to do this, no way should it be $450 + Labor. I'll bet the dealer has a special socket that goes right over it and a nice short handled air ratchet that blasts it off in 10 seconds.

The wrench cost me $8.00 at a local tractor supply store.