P0141 O2 sensor code, fun, fun, fun

[MTL_4runner]

Well I knew the 4runner was due for a problem or two since it had been running so flawlessly for so long. I drove home from my inlaws last night and wouldn't you know it, the CEL goes on. I looked at the engine temp immediately and shut off the radio just to be sure I wasn't missing any audible clues. Nope, drove ok, no studdering so I limped the short distance home. Checked the oil and coolant and both were fine so I went in and got my Auterra OBD code reader (that thing is a godsend!!!) to see what the deal was. Plugged it in and right away, the code popped up.

P0141 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

So since the truck was already warm I used the graphing function to just take a look and see what the front/rear O2 sensor outputs looked like back to back (the front sensor should be a nice sine wave and the rear should be fairly flat at idle near the average voltage for the first.....ie halfway between the high and lows on the sine wave). Well, the front one looked fine, good sine wave (looked to be burning just right, not too lean or rich). The rear one's voltage output was through the roof.....I mean flatline at the top of the graph (solidly over 1.25V) which means that yes, the sensor is definately TOAST. So I called up the local dealer to get a new sensor and they wanted $257 CDN for it......I almost spit out my drink......WTF, are you kidding me?! So now I need to get one shipped from the US because there ain't no way I'm dropping cash like that for an O2 sensor (maybe Evan, Phil or URD might be able to help me out on the cross border deal?!). I can't imagine how much they'd want for an A/F sensor up here, dirty buggers!

Will report once I replace and the code is gone, but I think it's gonna be pretty straight forward. The big deal is going to be getting the nuts off since I am sure they're pretty bad after a few winters up here. I'm gonna try some of the suggestions here and I'll give my verdict on what worked best from what I try.

[MTL_4runner]

I was under the vehicle today just to see how bad the nuts were on the studs that hold the O2 sensor on the flange and yep, they're bad alright. I soaked them a few times in penetrant in the hopes I can get them off with a pair of vicegrips (there's almost nothing left to use any sort of socket on).

Here's a good set of info on code P0141 in case someone has the same problem later:
http://www.4x4wire.com/toyota/4Runner/tech/O2_Sensor/

P0141 Oxygen Sensor Heater Circuit Malfunction(Bank 1 Sensor 2)
When oxygen sensor heater operates, heater current exceeds 2.35amps (2 trip detection logic)

Possible causes
1) Open or short in heated oxygen sensor circuit
2) Heated oxygen sensor (most likely)
3) Engine Control Unit

Looks like the part I need is Denso # 234-4154 which is the rear O2 sensor.
Anyone know what the Toyota part number for that is offhand?

[MTL_4runner]

Nevermind, I found it on my old sensor (no fun crawling under on my back in the snow!)
Anyway the Toyota part number is 89465-35380 for a Denso rear O2 sensor.

[MTL_4runner]

Just a word of note in talking to the dealer about O2 sensors. Evidently the part number on the sensor itself may not be the same as the Toyota part number for the sensor your looking for at the dealer (ie the P/N as written on the sensor from parts assembled at the factory may not exist when the dealer looks it up). It turns out the actual Toyota P/N is 89465-39855 for my rear O2 sensor.

[MTL_4runner]

Still waiting to get the darn part of this so I went out to the truck just to verify that the sensor was in fact toast. If you take a DMM and check the resistance on the heater circuit (when you touch two of the pins side by side, one pair should have a resistance of 11-16 Ohms) then if you find all the pin pairs indicate and open circuit (ie infinite resistance) then the O2 sensor is bad and needs to be replaced. Needless to say, mine was completely open on all pin pairs and I compared it to the front sensor just to be sure.....yep, front had the proper resistance on one pair.

I just wish it wasn't so hard to get cheap parts up here.

[MTL_4runner]

Finally got my O2 sensor from URD yesterday and went to Toyota this morning to get the nuts for attaching the sensor to the studs (because the ones on there now are rusted to oblivion). Dang dealer wanted $8 CDN for 2 friggin nuts!!!! So I bent over and pulled out the old credit card as usual.

I'm going to put it in this weekend so I'll post up how it went.

[MTL_4runner]

Ok I installed the new sensor when I got home from work and all went well. I wish I had taken a pic of the OBD reader so people could see what the sensor output looks like when the heater is bad but basically the voltage was just pegged at over 1.25V (the limit on the scale since O2 sensors should never go above 1.0V). I did take a few pics of the process for people who do this later. The nuts came off with alot of PB Blaster and a pair of vicegrips.....process was very tedious and watch your knuckles on the heatshield. Also be sure to scrape off all reminants of the old O2 gasket. This was also a major PITA and even required a heavy duty gasket scraper and a few small blows from a cold chisel (careful not to damage the metal sealing surface on the O2 sensor bung) to dislodge all the remaining gasket material. A few extra minutes here can save you alot of headaches later.

Here's the ugly mess I had to start with (sorry, bit blurry)


Here's the old sensor cut open to see the failed heating element (amazing, the element had just shattered)


Here's the old O2 and new URD sensor ready to go in (gasket was included, nuts are not!)


If you have a thread chaser set it works great for the threads on the studs (8 x 1.25 mm)


Finally, the new O2 installed and working 100% again


If you got any questions gimme a shout.

[arjan]

When I replaced my engine I bummed the pair of O2 sensors of him that came with that engine. They throw them out anyway and I got a pair of O2 sensors with 20K Kms on them.
When I put them in the nuts came of easily, I just need the socket 1 size down from what they should be.
When I used to go around that junkyard I made a habit of picking up bolts & nuts etc. laying in or around the 4Runners (or any toyota for that matter).
Also grabbed quite a few of the old 3.4, it's quite handy to have a pile of backup bolts & nuts in a bucket.

[MTL_4runner]

I wish we could reuse bolts like you guys can out west, everything out this way even if they're only low mile items, are usually in rough shape. There was really nothing left to put even a smaller socket on. I could have used a bolt extractor but a set of vicegrips worked well too. You can see what was left of the nuts in the 3rd pic down.....they were TOAST.

[Tanto]

Dang Jamie.  You were really busy occupying yourself in your own thread

It reads more like a write-up than a tech thread since you have a tendency to figure stuff out on your own!