P0138 Oxygen Sensor High Voltage requires ECM replacement?

I have not replaced the front/upstream sensor in bank 1. Good to know that it's best practice to replace both sensors in the bank at the same time. It looks like it's part 89467-0C010 which is ~$200, or

$124 Denso 234-9051 Right-Bank Upstream with 4-Wire 8.5” Option Air Fuel Ratio Oxygen Sensor

Denso 234-9051 at ~$100, and it's the same part in both banks.

I just measured the resistance according to the manual and it seems reasonable (3.0Ω at 85°F). I guess I should measure the other bank as well for a comparison. Maybe I could swap them to see if it makes a difference before I throw more money into this.

 

While I agree that's a good reading for the heater element of the sensor, pins 3 and 4(AF+/AF-) are the money makers when it comes to sensing the oxygen.

If that has not been mentioned already, that is very good way to tell if it moves code to other side....result should be P0156

 

Ah, good point. So swapping is the only way of testing the sensor. I ordered one of those special Oxygen Sensor wrenches with the swivel head and bent handle. I have a trip coming up so will probably try this out in a few weeks. Sounds promising.

 

Finally got around to swapping sensor 1 in the two banks. Man, bank 1 (driver side) is very difficult to get at, even with the specialty wrench. And it was super loose, barely finger tight. Maybe because of the limited access. Bank 2 is much easier to access. Anyway, after several days of driving like that I finally got a code, P0158, same error, other side. So that tells me the sensor needs to be replaced. At least it's on the easier side now.

Is this a part where I should stick with a Toyota original, or is Denso going to be fine here? And what's the general consensus about Amazon, can it be trusted for Denso parts? If not then at Autozone the Denso is about the same price as the original, so I'd just buy from the dealership at that point.

 

Denso from Rockauto (not A-mazon or e-Bay or Wally-mart .com) is the consensus

 

Yup ^^

Denso. Use the part finder at their site to find the part number by plugging in your truck info or VIN and choosing 'Sensors' checkbox: https://www.densoautoparts.com/

Don't get confused with the output. They always list at least one "Universal" sensor in the lot. Pay attention to which is upstream or downstream in the part details.

Sometimes they also have further details like "for manual transmission trucks..." or "for 4WD" for example. If you need a sanity check, reply back in here.

Take the part number and plug it in at Rockauto or Summit Racing or your preferred non-fleaBay, non-scAmazon, non-WallyWurld vendor's wwebsite and order it up.

Glad the swap-between-banks test worked out for you. Great way to save a buck.

 

Thanks for the parts house recommendations.

In going back through the Service Manual I notice that sensor 1 is only mentioned in the V6 section. Didn't see that before.



It's not there in the V8 section.



I also missed shifty's suggestion about sensor 1 the first time around.

 

It's all good. My brain is a mess the last few weeks and I dunno why. I keep little details on here, and made a few invalid statements because my brain isn't functioning or I'm thinking of the wrong shit (which I pretty consistently do anyway, but it's at peak here lately). Lack of sleep? Sjogrens maybe flaring up again? Tend to be in a fog when it does. I often can't keep up with who has what, I should probably read back to the beginning on every thread

I'm thankful there's others on here like @BubbaW and @Aerindel to chime in.

But anyway, I looked it up, this is what Denso is listing for you - looks like 4WD and 2WD are different, where your 4WD has a different downstream sensor bank 1 vs 2:

​

 

As you suggested it was a pre cat sensor that was causing my friends p0138. Same as OP, local shop was saying it was ecu.

 

If it's not a shop that focuses on Toyota, this is why I don't recommend to shops that don't advertise as Toyota specific.

There are a few quirky things about Toyotas I've learned over the last decade or so of driving and working on them, which don't match the primarily GM, Honda, and VW vehicles I owned prior. While I wouldn't necessarily say this is one of them, the code (to me) screams "replace the front (and ideally the rear simultaneously) O2 for this bank", I can see why others would look at other stuff.

There've been a couple times on here where the ECU legitimately was a problem. I haven't seen it yet with this code though.