Trying to Decode my Error Code(s)

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Strange thing happened the other night. My check engine light flashed for like 5 seconds then went out. I've never seen it do that before. I parked for a while and when I got back in the truck, it was on solid - now that I have seen before.
I used to get the light on for a few days each month due to O2 sensor issues. But then that stopped for a while, a few years at least.
But back to last night, after the flashing, I was at a red light and the engine started to run really rough. It was almost like it was stalling, but the RPM wasn't going down, it was steady about 550 rpm - which is normal for warmed up idle on the 5.3.

Then I remembered my ODB thingie can read codes. So I did the diagnostic report. (attached)

Everything looks fine except: "Exhaust Gas Sensor Heater Monitor Bank 2"
What is that? The word heater in that label really confuses me.

This is the first time I read the codes myself, every other time my mechanic did it and verbally told me what it was. So I don't know if this is the same issue, or a completely different issue?

Does anyone know what all this means?
 

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  • Diagnostic Report 2023-01-30 111359.pdf
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TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
Sounds like the pre-heater on one of the O2 sensors bit the dust.. Do you happen to have the actual code?
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
I attached the report on the first post. I don't fully understand what all of it means but it looks like the codes are:

P0050
P0155
P0050
P0059
P0155

So the sensors have heating units on them? Where is that located? Is it easy to replace?
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Interesting. So the heater is just part of the sensor. So saying the heater is bad is basically the same as saying the O2 sensor is bad, from a practical, parts point of view.

Question
I looked on rock auto and it lists upstream and downstream sensors and some even list upstream left, upstream right, downstream left, downstream right. As if all 4 sensors are different. However when you go to a site like napa.com, it just lists one sensor. Are all four actually the same?

Also if I'm going to replace one of the upstream sensors due to error codes, should I just replace both upstream sensors? Given that they're not painfully expensive and they're both going to be 150,000 miles old at this point?

O2 sensor wrench, do you need one of these or can you maybe get by with a box wrench? From what I've seen in youtube videos, It looks like this little wrench would be very helpful but figured I'd ask anyway:
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
I'd follow what NTK says and use those since they used to supply ACDelco. Sometimes they are the same for both sides, just different wire lengths and some suppliers will just say to use the same number for both sides, which will have the longer wire. Nothing wrong with that except you might get a bit of extra wire.

The funny thing is that the GM one says DOWNSTREAM PRE-CONVERTER, which are totally opposite. Downstream is POST converter. Upstream is pre-converter.
 

Beacon

Member
Mar 22, 2019
445
SouthWestern PA
up stream is, different from downstream, I would buy Genuine GM, although maybe someone else could point you to a different brand of O2 sensors that work. I had trouble with using aftermarket O2 sensors in a jeep, and it left a bad taste in my mouth and wallet.
 

Beacon

Member
Mar 22, 2019
445
SouthWestern PA
The funny thing is that the GM one says DOWNSTREAM PRE-CONVERTER, which are totally opposite. Downstream is POST converter. Upstream is pre-converter.

I even looked for one from advance auto and their description says the same thing.

Exact Fit for your 2008 Chevrolet Trailblazer LT
GM Genuine Parts; Downstream; PRE CONVERTER; 2 Req.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
NTK have been good to me. I've had issues with Delphi in the past and they're not the same company they used to be. Haven't heard anything good about Walker. Haven't heard anything at all about Bosch.
 
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TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
NTK has been good for me as well. NTK used to make them for GM.

For O2 sensors, you have to replace them in pairs, at least thats what is recommended. Pre and Post on one bank should be done together.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
The post-cat ones I'd just replace the one. Those only report on cat efficiency, which we don't really care about, unlike the pre-cat where it actually affects fuel trims so there you could have an imbalance between the banks if one is lazy.
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
My report doesn't indicate any problems with my post-cat sensors though, does it? And it the pre-cat sensors are only $37 and can affect the way my engine runs, seems logical to replace both? The bad one and the other one?

The other question is, who here has a heated garage I can borrow? :biggrin:
 

TollKeeper

Supporting Donor
Member
Dec 3, 2011
8,047
Brighton, CO
I do.. But a VERY long way from you!

If I am remembering right, the V8's on these trucks make doing the O2 sensors a pain in the arse!
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Yep, bank 2 sensor 1 errors, which means passenger side upstream. That one is a bitch only for the connector, which is tucked behind the rear of the head. Undoing it isn't too bad but reconnecting it, there's only room for one hand going through the wheel well and the connector wire is short. It might be easier to first connect it and then drop the sensor down the exhaust pipe. Pre-twist the sensor's wire in opposite direction of screwing it on the exhaust pipe and screw it on.

If it's really rusty and stuck, use a 22mm 6 point deep socket. It's a little tighter than the normal 7/8 sensor socket and won't spread out because of the slit. I've actually modified a 22mm impact socket with a slit for this. Works a lot better and won't spread while reefing on it. Just use an open end wrench to torque the new one gently. Don't forget the anti-seize.
 

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
I finally had time to climb under the truck and get my eyes on these sensors. Holy shit guys, are you serious??? This is going to be a nightmare. Unless these little shits are somehow not stuck AT ALL, which seems very unlikely since they are probably original. I did spray them with some penetrating oil. I'm going to do what one youtube video said and keep spraying them periodically up until the time I actually try to remove them. I'll be ordering the new sensors very soon. I will be very glad to finally get these annoying orange lights off my dash (also going to finally buy new TPMS sensors)
 
I finally had time to climb under the truck and get my eyes on these sensors. Holy shit guys, are you serious??? This is going to be a nightmare. Unless these little shits are somehow not stuck AT ALL, which seems very unlikely since they are probably original.
Good luck. I replaced what I think were the original O2 sensors on my new-to-me '97 K2500 plow truck. I had to remove one exhaust pipe to get the sensor out. All four of them needed to have the female threads reworked with the Lisle rethreading tool.
www.amazon.com/gp/product/B000XETMW0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1


Half the reason to remove O2 sensors on a semi-regular basis is that--completely aside from the fact that they get slow "lazy" as they age--they get seized in the female threads if left too long. Even if the sensor works perfectly--and it probably doesn't at that mileage--unscrewing the thing, replacing the anti-seize, and putting it back in prevents problems later.

When it's me, I tend to not leave them in more than 80K--100K miles, and once out, they're replaced with new.

I did spray them with some penetrating oil
ABSOLUTE WASTE OF TIME. The thing is sealed gas-tight using the same sort of gaskets that sealed older spark plugs--which could hold the enormous pressure of combustion. Penetrating oil cannot get into the threads to do any good.

Penetrating oil will make a lovely puddle on the ground where it drips off.

Keep in mind that when O2 sensors are not seized, an O2 sensor wrench "can" be very handy. When they are seized, an O2 sensor wrench is as useless as penetrating oil, but even more dangerous. My limited experience with O2 sensors is that you're more likely to find seized ones than easily-removed ones; because nobody removes them on time--they're ignored until long past due. Therefore, O2 sensor wrenches are fabulous for INSTALLING sensors, and fairly worthless for taking them out. Add in the popularity of cheap-junk bottom-feeder tools from Communist China (TSOs--Tool-Shaped Objects, they're not really "tools".) and pulling O2 sensors can be an ordeal. If you round-off the corners of the wrenching surface of the sensor because your O2 sensor wrench flexes at the split for the wire harness, you'll be in real trouble.

I bought a "special tool" for doing O2 sensors that don't want to unscrew. This is a deepwell, impact socket in 1/2 drive, and what makes it special is that most deepwell impact sockets aren't broached the full depth of the socket. This one is, so the body of the O2 sensor fits inside once you clip the wire harness off. It's made by Wright, a family-owned tool company that makes quality product in the USA.

www.amazon.com/dp/B002VKBRCC/?coliid=I3QM27R5Q6EZ28&colid=2VLYZKC3HBBDO&psc=1&ref_=lv_ov_lig_dp_it


I use an impact socket for strength and rigidity, not because I use an impact wrench on the thing. A long-handle ratchet works wonderfully.

Although...sometimes you get lucky. My most-recent O2 sensor debacle was on an '05 Ford Focus, owned by a friend-of-a-friend, semi-destitute. Everything I've touched on this car has been a disaster--rear brakes had failed wheel bearings in the drums, a tire had shifted belts, the car shook like it was having an orgasm at 60 mph. Doesn't idle right. I fix all that, take it for a test-drive, and the instrument cluster goes dead every time I get to 30 mph. Comes back to life at idle. The alternator failed while I was working on the brakes, the instrument cluster would shut-down to protect itself because the alternator was throwing 17 volts when the engine revved-up. This alternator was two months old. The computer had a dozen "codes" and the O2 sensors are probably originals. I decide to replace the upsteam sensor "just because".

So I get under it, looking at the O2 sensor. I can just barely get a sensor wrench on it. And Wallah! It unscrews just like it's supposed to. It's a miracle! Praise God!

As I'm wiggling out from under the car, it occurs to me that I've just pulled the DOWNSTREAM sensor instead of the upstream like I'd intended. So back under I go, and reinstall the downstream sensor with fresh anti-seize.

The upstream sensor had to be accessed from the top side, with my Wright socket, and extensions, and a universal joint, and the longest 1/2" ratchet I own, with a cheater pipe. And harsh language. Lots and lots of harsh language.
 
Last edited:

l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Ok looks like Friday night is when it's going down. I'll be borrowing my uncles garage and hopefully all goes smooth.

Question: Planning for the worst case scenario, if either the threads in the pipe get destroyed when I unscrew one of the sensors, OR if lets say one of the sensors snaps in half leaving the threaded part stuck in the hole, will the truck still drive? With no upstream O2 sensor attached?
I know I'll have to get it fixed quick but I'll still have to drive it home Friday and then get it to a shop, if everything goes wrong.

Hopefully this is moot, hopefully this goes as well as the wheelbearing went. Actually hopefully it goes better, I do think I snapped one of the caliper bolts that day. But still, better safe than sorry.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Yes it will. The PCM will use preset parameters using the other sensors. In fact, one test we do to check for clogged cats is to remove the upstream O2 sensor and drive it.
 
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l008com

Original poster
Member
Feb 19, 2016
886
Massachusetts
Ok I got to work tonight and well..... things went spectacularly bad!

So first things first, I watched this video to make sure the sensors I was looking at, were right right sensors:

Now, I can't explain how... both are 5.3's, both appear to be 4x4, mine is an 08 and that one is an 06 I think he says, or maybe 03? I don't know but here's the thing. The sensors in that video have SIGNIFICANTLY more space around them than mine. In the video, you could easily put your hands right up to the sensors. On mine, I could barely even get the socket wrench up there without twisting it all around. Maybe the transmissions in the later models got much larger or something? I dunno but it was NOT easy accessing the sensors.

But with a lot of fighting, I was actually able to get to them. They both broke loose pretty easily and unscrewed without any real issues.... excluding the issue of the tight space and not being able to move the wrench enough to be able to reset it and crank again. It was a pain.

BUT I was able to unscrew both sensors. Once they were hanging, then it was time to find the plugs and unplug them.

This is where things went from bad, to complete failure. There's tight spaces, then theres what's going on under my truck. The best I could do is literally get one finger tip on the passenger side connector. No possible way I could unplug it, no possible way I could have put the new one on there. I tried reaching down from the hood, behind the engine. I tried reaching in from the wheel well, and I tried reaching up from underneath until almost my whole arm was up in there and I still wasn't even close! Both connectors seem to be more or less behind the engine, on top of the transmission! This is madness! These sensors could just have longer wires and the plugs could be anywhere. Why bury them making them impossible to replace?????

Unfortunately I didn't take any photos but the clearances were significantly less than anything I've seen pictures of on the 5.3 TBs.

I ended up just threading the old sensors back in so I could drive home. Without anti-sieze because I don't have any, the new sensors have it pre-applied and I don't have any more. But hopefully it's ok because I'll be taking care of this as soon as I can.

So unless anyone knows any secret way to get at these plugs, I'm probably going to end up bringing my truck to a mechanic next week.... to install the sensors I already purchased, which I know they love. Although to be honest, I don't know how a mechanic would be able to do this either. It looks like something has to be significantly disassembled, like everything on top of the motor so you can reach behind, or hell, dropping the transmission entirely. I know it sounds like I'm being overly dramatic but if theres an easy way to get at these plugs, I'm not seeing it.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
That passenger side connector is a bitch. IIRC, I unhooked mine from whatever bracket it's attached to, which gave an extra inch or so to play with. I think I pried it out. After reconnecting it, I didn't put it back on that bracket. Driver side was a little easier. I also recommend reconnecting them first and then screw them back in so you have that extra wiggle room.
 

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