AutoZone Says Codes P0135 and P0161

2002 AC Limited 4x4 4.7 L V8
After replacing all the bulbs in the instrument cluster, I discovered that the Check Engine light was on. The local AutoZone plugged in their diagnostic tool and was able to read the codes, but their computer didn't recognize the vehicle. After the AZ tech somehow manually selected the vehicle, it showed codes

P0135 (O2 Sensor Heater Bank 1 Sensor 1)
P0161 (O2 Heater Circuit Bank 2 Sensor 2)

However, now that I'm looking at their printout, I see that it describes the vehicle as "2WD" instead of "4WD". So, that makes me even less confident of the codes. My brother also has a diagnostic tool, so I'm going to plug it in tomorrow for a second opinion. If his concurs with the AZ diagnostic, I'll be ordering all 4 sensors (Denso parts) from Rock Auto as suggested here. So, my questions are:

Are the codes different between 2WD and 4WD?
Where can I find the socket sizes and torque values for upstream and downstream sensors?
Is there a recommended O2 sensor socket for upstream?

 

OBDII codes are OBDII codes. They're basically a standard, so what you see is probably going to be what it is across most makes & models. I've seen cheap scanners parse incoming output incorrectly, though, like they misinterpret what the ECU is outputting and interpret that as a totally different code (like, it sees some data from ECU and interprets its format as another code). So a doublecheck isn't unwarranted, but highly unlikely the code they pulled is wrong. However, if the ECU did report itself as being a 2WD ECU, I'd be curious if your 4WD is working. It's possible 2WD is just what the parts store computer defaults to, or what the employee manually put in.

For the wrench/socket, any clawfoot in 22mm or 7/8" will work, online and available in local stores I see OEMTOOLS 25249 or ARES 70039 as good options for under $20.

FSM has torque specs and is available for download in the new user info megathread. If you haven't downloaded a copy, what the fuck are you doing? Get on it, Hoss, they may not be available for download tomorrow.

Note that many vehicles also use a gasket with the sensor, not necessarily on our trucks, just saying, always check first in the exploded diagrams.

Note that upstream is often called "Air/fuel ratio sensor" and not "Oxygen sensor".

Note that you should replace in pars, so if your O2 upstream bank 1 and downstream bank 2 are bad, just replace all four at once.

Don't buy your parts on scAmazon or Autozone.

Only buy 'Exact fit' part found at www.densoautoparts.com, not the 'universal' (never cut your OEM harnesses for anything, radio, O2 sensors, NOTHING).

Note that sensor part numbers can vary on our trucks depending on:

• Drivetrain (2WD/4WD)
• Engine (V6/V8)
• Cab type

Always look up part numbers first. Always use the EPC-DATA site to look at your exploded diagrams to verify if you need gaskets or other extras. After you complete your VIN search at EPC-DATA site, your sensors will be under "Electrics" top level section, probably in the 1st schema as you see here.

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Okay, I feel better now, but I'll still get that second opinion. Since I borrowed the truck, I've been engaging 4HI for a long, straight stretch of road I drive into town to exercise the system. I hear and feel a distinct engagement when I depress 4HI.

Okay, my dad has a 7/8" sensor socket that I can borrow. Might pick up a 22mm just to have.

Downloaded and searched that manual already, but as I found out here I don't always get the search terms correct. I'll double back on that.

Dude, I said in the OP I was going to follow your instructions here. Cut me some slack. Admittedly, it's been a while since I did much wrenching on a vehicle. Maybe I don't fully understand how this EPC-DATA thing works. The site buried the sensor(s) under "Switch & Relay" and then tied all 4 sensors to a single line item in the parts list.


Even more interesting, is that when you click on that single number, it shows a different (more complete?) part number for each of the Front RH, Front LH, Rear RH, and Rear LH sensors.

Yet, Denso only lists 2 different OEM parts: a Rear (Downstream) sensor for 4WD (2 required) and a Front sensor for all (2 required). I did answer all of Denso's questions about my vehicle.

Also, a little searching turned up these two how-to videos. The second video leaves a little to be desired because they don't show all the mess they had to go through to remove the old downstream sensor.

 

I'll get to the other stuff in a minute, but for now ... don't bother, save your money. They're effectively the same thing, close enough you don't need an exact 22mm.

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Interesting. Yeah, there's some variation there year to year.

But that said, your truck is clearly one with gaskets too. Line item just above the one your arrow points to.

Oh, and not trying to harp on you.

Interesting. Never seen anything like that.

Stick with what Denso is telling you, since you're not buying/needing to buy Toyota's boxed iteration of Denso. I wish I had a definitive answer for you on that one, why the Toyota explodeds are different. I'm sure there's a reason, but I can't tell you what it is. Notice only the last two digits of the Toyota EPC part number changes by ten. Usually those last two digits are different when there's a slight part trait change, different shape, length, etc.

 

@Neo get under your truck and take a look at your downstream sensors and see what your fasteners look like. The nuts on mine were rusty, I've still got one of my originals on because it was such a pain to try and remove. Do this just so you can figure out how long of a job you'll be in for.

 

Dropped by my brother's house today and he ran his OBD2 tool on the 2002. It pulled the exact same codes as AZ. So, headed over to RockAuto.com to order the parts shortly. The downstream sensors from RA include gaskets. So, I just need to pick up 4 of the 90179-08059 nuts from the local dealer.

 

You can just go to the hardware store and get M8 x 1.0 Stainless Steel hex nuts (I don't remember if you need lock washers)

 

Don’t forget the antiseize

 

We did a little exploratory work as suggested by @NickB_01TRD. The nuts on the downstream looked pretty good. Seems like those little shields may have kept a lot of road crud from getting to them. I applied Kroil, waited a while, and the nuts broke free with just a 1/4" drive socket wrench! Tightened them back up until the parts arrive later this week. I also checked the fit of the sensor sockets we have. The longer one seems to work better, but I was working mostly by touch. The fit may be better after the electrical cord is unplugged. I think we're ready to go for Thursday. Here's the Dynamic Duo of Gen 1s I'm helping to maintain. The left is the 02 AC LTD 4x4 4.7 owned by my brother and currently on loan to me. The other is my dad's 03 AC SR5 4x4 4.7.

 

Awesome! Interested in feedback, if this solves things for you.

And just echoing what @bfunke said: Don't forget the anti-sieze on the threads of your sensors, just don't get it on or in the perforated cap part. I prefer Permatex's anti-sieze over CRC.

 

Will definitely post feedback once the new sensors are installed. I've got torque specs and anti-seize in hand.

In a twist, the package just arrived from RockAuto. The upstream sensors are what I expected. However, the downstream sensors did not include the flange or the gasket despite being advertised as such. Didn't see a phone number for them, so I sent email to their preferred help address. We'll see what happens.

 

I've been given shit on here in the past about recommending Summit Racing over RockAuto, but what you just described is the main reason I usually try to push people toward SummitRacing. They have a verified supply chain, killer customer service, and typically have identical prices +/- 2-5%, and faster 2-day free shipping. It's honestly a better deal. But I also realize I'm biased, I have a brick and mortar for them 30mins from my house so I can often pick up same-day if I want.

But yeah. That's my main rub with RockAuto, and why I will always recommend Summit over them.

 

They responded pretty quickly by email and directed me towards their "Help with Existing Orders" page. I was walking through the complaint process and decided to double check the sensors in the boxes. I only opened one upstream and one downstream box to check at first, so I though I'd open the other downstream box. Much to my surprise, it had a flange and a gasket. I went back to the box I'd already opened and that one had a flange and a gasket, too. In my defense, I've been sick for over a week. Finally got to the doc yesterday and I'm beginning to wonder if the prescription they gave me is having some side effects. Don't worry, I'll have adult supervision when doing the work on Thursday.

Thanks for the tip on Summit Racing and apologies for the false alarm on Rock Auto. I gotta get some sleep.

 

We got the 02 up on ramps today and the downstream sensors were a relative breeze. Even the gaskets came off in one piece. Both the upstream sensors were pains in their own special ways, but we got those swapped out as well. Disconnected the battery for a few minutes, reconnected it, and fired it up. There was no sign of the Check Engine light. Drove it about 12 miles from my dad's place to my home and still no sign of the Check Engine light. @shifty` you asked for an update and so far this appears to have solved the problem. Oh, and the doc did swap out my meds. Feeling straight now.

P.S. I didn't forget the anti-seize!

 

Now go enjoy problem-free sensor operation for another 22 years

In all seriousness, if anything on the exhaust/emissions side of things comes up again, I'd be hunting for leaks or wiring. And on a proactive note, 22 years is a long time for rubber, so do consider updating some of the many rubber vacuum lines around the engine bay.