p0137 and p0158 at the same time.

New here and new to working on cars but I’m trying to learn. Anyways, just got a 2006 tundra with 108k miles. Its very rusty but is in ok shape otherwise, i suppose.

My state requires e-checks so I was doing the recommended driving pattern to get the system diagnostics to run. I was greeted by the check engine light coming on and codes p0137 and p0158. I don’t have a scanner, I just used the report from the e-check station.

I’ve been looking at the official mechanics manual online and some of it makes sense but I’m a little lost as to where I should begin looking for problems. It seems odd that both sensors would be bad at the same time with opposite voltage codes, so I’m assuming the problem stems from upstream of the downstream sensors?

 

First off, both codes point to issues with your O2 sensors, and they're related to voltage high or low, so it could be that the wiring is fine (or not), but the sensor is shot, or someone used a non-OEM brand, lesser-quality sensor, or spliced your wiring to install a non-OEM sensor, or some other event happened to trigger this.

O2 sensors are one of those parts where you only want to buy OEM (Denso/Toyota) brand. And whatever you do, you DO NOT want to buy auto parts off scAmazon or fleaBay, you may get counterfeit parts, it's a legit concern, it's happened to members here and continues to happen more often these days.

Second, any local auto parts store chain will scan codes for you for free. If it's a major chain, they'll often print off a report for you. Use that to your advantage.

That said, in checking this information thread I recommend reading if you haven't already, I see you have a V6, the newer VVTi version, the 1GR-FE. I see the codes you listed, are:

• P0137 => Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)
• P0158 => Oxygen Sensor Circuit High Voltage (Bank 2 Sensor 2)

Basically, codes can't always be taken at face value, sometimes the ECU (on-board computer) gets it wrong. But those two codes suggest both of your rear O2 sensors are having issues. If this just popped up out of the blue, that's weird for both to suddenly have an issue, unless a shared ground or something went bad, or ... I'd ask you ... did someone steal your cats in the not-so-distant past and you had someone replace them? Like, maybe they cut the rear harnesses, or took the rears completely with them? It's hard to miss the sensors (see video below, which also explains all the 'bank' and 'sensor' number stuff. Since you want to learn, this video will give you a rundown of what you're up against, but I'm not telling you to watch this and suddenly feel empowered to tackle the problem - hang out, talk to us, let's talk through things. Start by giving us some pics of the sensors and wiring.

https://www.youtube.com/watch?v=UJ-tqfqztd8​

 

PS - the thread I linked above, in one of the 1st couple paragraphs, has links to the OEM service manual. This is taken from it, and it does a decent job of (Toyota) explaining why someone would see these codes, and gives a technician the places to start investigating. This isn't in plain English, and again, some interpretation/prior knowledge is probably helpful if not actually required, but ... Just so you can maybe grasp things a tad more. And FYI, you'll want to download a copy of that manual and store it somewhere safe.

If this was a P0137 and P0138 (I assume you didn't typo things right?) this code would make a lot more sense to me.... Did you typo things? If so, you should be able to resolve easily by popping in new O2 sensors on bank 1. Always best to replace in pairs, and if rust is common in your area, expect to have a fight on your hands.

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Hi, thanks for responding, and thank you for the resources, I will be sure to look through them.

Unfortunately, I did not make a typo, I have p0137 and p0158. Also I’m not sure if the catalytic converters were stolen as I just got the truck a month ago from a private seller, however, the rusting on the cats and the exhaust pipes seem to match.

Visually, the situation looks about the same on both downstream sensors. The sensors themselves seem to look ok to me, but the exhaust pipe connections to the cats look rough. In the first picture I included you can see that a bolt appears to have rusted off when comparing it to the passenger side cat connection (second picture). Another thing to maybe consider is that the wiring harnesses seem to have rusted out of their brackets identically on both sensors, not sure if that could be causing a grounding issue or something similar?

 

The one observsation I'd make is the 1st pic, you can definitely see is a DENSO part, it's screened on the side. The 2nd pic looks it, but definitely looks older. Then when you get to that last pic, very clearly, look at the age difference between those two connectors. I presume that's the same as the 1st picture with 'DENSO' clearly visible. If you look high up in the 2nd pic, you can see Sensor 1 for that bank (see below).

All that to say ... again, you said you want to learn, so I feel like me and anyone else on here can chip in with their thoughts.

If it were me, my one commonality between these two, other than the fact they're both O2 sensors, is both codes point to wiring faults of some sort. So that's probaby where I'd start testing, if it were my truck.

That thread I linked above also has links to the EWD / Electrical Wiring Diagrams for these trucks. I suck at reading them, but I'd probably crack them open to try to understand how the rear O2 are wired and if they share a common circuit. Just because they're a PITA for me to personally read, I can't expect you to read them. However, I know @Tundra2 had some issues with his O2 wiring, not sure if he ever asked Bruce how he troubleshot it or figured it out. I swear I've seen @BubbaW help someone break down O2 wiring (he's 100x better than me w/EWD), I also wonder if @RainMan_PNW may also be good at EWD breakdown? Are the rear O2 linked? Is there a common plug that may've corroded OP can check?

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Just a quick note before going out to dinner.

As shown in the chart above, P0137 Bank 1 can also be "Gas leakage from exhaust system" and I bring that up because the below quote alluding to an exhaust leak due to bolt issue Bank 1 ? If understanding OP correctly.

 

Yup, only reason I didn't go there is because there wasn't similar cause on the other side. It's plausible there's two different sources for these codes, but (only with my luck) it'd be unusual for it to pop up suddenly - it's possible this issue existed when OP bought it, though, one of them, but wasn't dealt with, and the 2nd was natural?

But those are really the two big avenues I see to try chasing this down: The fact this is impacting both rear O2 sensors is totally related, or totally unrelated.

If it's totally related, I'm chasing wiring. If it's totally unrelated, my first suspect is exhaust leak on the bank with the new sensor, and a bad rear sensor on the other bank.

 

Busier than a cat covering up shit at the moment, but i might have some time later tonight or this weekend to read through this and see what I can share

 

Not sure if you guys are still following, but I found the vehicles e-check testing history which could potentially shed some light on things.


All of the 2023 testings were done by me, the rest were done by the previous owner. As you can see p0137 and p0158 have a history with the vehicle. I think this could help narrow some of the troubleshooting down but let me know what you guys think?

 

I think all extra info possible is good info. Big question is: Why are those two codes popping up?

Especially confusing is, clearly the previous owner took at least one of the codes (interpreted literally) and changed one of the post-cat O2, just wish the source of that part was known. Thing is with taking it literally, sometimes, with some emissions codes, like when the post-cat O2 gets flagged, it's actually problems with the pre-cat O2 that triggers the ECU to blame the post-cat sensors.

But as @BubbaW pointed out, there's a few of potential causes here. Could be related to wiring/ground or corrosion in a connector upstream from the O2 sensors. Depending on how the VVTi V6 is wired, could be a problem with the front O2 sensors is triggering issues with the rear sensors. Could be a combo of one bad post-cat O2 (P0158) and, say, an exhaust leak (P0137) from the mangled side w/new post-cat O2 sensor, the former owner just took the code literally. A few questions for you:

What state are the pre-cat O2 sensors in, when you look at their body, look at their wires and plastic connector, do they look original? (take the existing 2 pictured above; note the differences; use the clearly-new one as a reference)

How willing to work on this are you, what tools do you have, what are you capable of?

How much money do you have to throw at this? Like ... for example, is taking the truck to an exhaust shop to replace and/or repair everything from the cats to the muffler an option? Is replacing the O2 sensors which clearly AREN'T as new as that newest one an option, financially, buying from RockAuto and not from a known-counterfeit-risk-source like scAmazon/fleaBay?

Note: Not saying an 'exhaust system leak', which could very well be the cause of P0137 has to be caused by that one bad joint, but the fact the code trigger is the post-cat O2, and the flange RIGHT BEFORE that post-cat O2 is pretty FUBAR ... it leaves me thinking that just cleaning that up and re-gasketing it could potentially clean that code up. "Could" being operative term. No reason it couldn't be a manifold leak, causing the system to get weird results.

 

Hello to those who might still see this thread.

Its been a while and a little progress has been made but not much.

Ended up taking the truck to a trusted and reliable mechanic and they ended up replacing both downstream O2 sensors. Initially, the check engine light was off when I drove the truck home but it came back on later in the day after taking a 2 minute trip on the freeway.

It seemed odd for the CEL to come on so quickly since the conditions were definitely not met for the O2 diagnostic driving pattern (10 mins between speeds of 40-70 mph). The manual also states that the diagnostics would not run for the O2’s again until the CEL was turned off. I verified that the CEL was on again for the same DTC’s

Today, I ended up taking the truck to oreilly’s to get the CEL cleared, and took it on the freeway to complete the driving pattern. I immediately went to the e check station and finally passed the emissions test!

Unfortunately, the CEL came back on while I was driving back from the license bureau (again weird because I wasn’t driving fast enough for the O2 diagnostic monitoring to occur). While its still possible, perhaps even probable, that there is another issue causing the codes; could it be possible that these codes are considered permanent in the computer’s memory? Is there a way to clear the computer’s memory without a scanner? Can I unplug the battery to give it a fresh wipe? I’m trying to ensure that there is indeed still a problem causing the DTC’s and not just some old codes thats are kicking around.

EDIT: Mechanic did mention that he checked the wiring for the O2’s all the way up to the PCM for any issues and found none.

 

No chance the codes are stored persistent.

I think you should change the upstream sensors if not already done (I'm not going to read thru all the text above). It's generally frowned upon to replace one per bank. If the downstream fails, replace downstream (after-cat) and upstream (before cat) on that bank.

 

Not sure if anyone is still following this, but I ended up swapping the lower O2 sensor harness plugs from one to the other some months ago. My CEL never came back on after that. I initially learned of this from the Tacomas forum, which makes sense, bc it seems like my truck has a lot more in common with tacomas than other tundras since it has the same engine and manual tranny (1GR and RA60) that was used in some Tacomas.

Just wanted to add a conclusion to this thread just in case someone should have a similar problem in the future.

 

When you say you swapped the downstream plugs, you mean you unplugged the passenger downstream, and plugged that to the driver downstream sensor and vice-versa?

 

correct

 

Is it possible someone swapped them prior to be on the wrong bank? In looking at mine, seems it would be a stretch to swap. But I’m not under the truck, just using pics.

 

Yeah it was a bit of a stretch. I considered attempting this fix when I initially started trying to diagnose the problem but figured it was unlikely because one harness appeared slightly shorter than the other and wouldn’t be long enough to stretch to the other side.

I don’t know if this fix works by another mechanism or if it was just swapped on accident beforehand. Not sure what someone could have been doing that would require unplugging them. Maybe transmission work ¯\_(ツ)_/¯