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Discussion Starter #1 (Edited)
Hi all. So I got my truck inspected the other day in NYS. Wouldn't ya know it, an hour after I got my sticker, the check engine light came on. It never has before. Glad it happened AFTER, or I would have failed. I've got a 2005 Tacoma, 4 cyl. I pulled the codes with a cheap scanner, and cleared them, but the light came back on, so something is up. The code I got is a P0137. Oxygen sensor, Bank 1 sensor 2, low voltage it says. After some research, and youtube watching, it seems to be the heated o2 sensor right after the catalytic converter. I ordered a new one from the parts store. Autozone, Advance Auto, and rock auto all had several selections for the sensor. I ordered the Denso 234-4261. I ordered it because it said the Denso one was the OEM sensor on Autozone's website, vs the other choices that just said "exact fit aftermarket part". Can anyone verify this is correct? Is that REALLY the OEM sensor? I don't really trust Autozone as a source of factory parts information. I really need to get a factory service manual.

The sensor should be here soon. I have had REALLY bad luck replacing o2 sensors in the past on other vehicles. It seems like I always need to order 2, just to get 1 good one. Anyone else have this problem? Same with parts store TPS sensors. Hopefully this isn't the case this time.

Can anything else cause this code? Other than an exhaust leak, or maybe a bad catalytic converter?

Anyone have experiences to share?

Thanks,
Matt
 

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Denso 234-4261 is the correct part for Bank 1 Sensor 2. The original sensors are Denso so you're fine using Denso aftermarket rather the Toyota Denso OE (part number 89465-04290). I did the same thing.
 

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Discussion Starter #3
Soooo......I put the new sensor in today, and checked for exhaust leaks up front. No leaks. Cleared codes, took it for a drive, and engine light is back on..... Same code. Any ideas?
 

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Verify that sensor signal wire is good to PCM.
Monitor the O2 voltage while doing a few snap throttles.
Looking to see a increase from .2v to around .8v.


If so then circuit/PCM good.


Are fuel trims normal with engine load?

Engine not running lean?
No exhaust leak around rear O2 sensor?
 

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Discussion Starter #5
Verify that sensor signal wire is good to PCM.
Monitor the O2 voltage while doing a few snap throttles.
Looking to see a increase from .2v to around .8v.


If so then circuit/PCM good.


Are fuel trims normal with engine load?

Engine not running lean?
No exhaust leak around rear O2 sensor?

Thanks. I plan on scoping out the wiring tomorrow. I am aware an open wire, or bad connection could cause this. I will wiggle things, and take some readings. I will also watch the voltage and try that tomorrow and make sure its in the .2-.8 range. I don't believe the engine is running lean, no symptoms. If anything, I'm burning MORE fuel than normal. Not sure what you mean by fuel trims..... I verified there is no exhaust leak before or after the o2 sensor, anywhere close....or anywhere really.
 

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If the wiring checks out, and the new sensor checks out (it IS possible to get a bad Denso/Toyota/Japanese part out of the box), then have the battery tested.

A few years ago I was working on my accountant's '00 RAV4, which had several codes. One of which was a code for the upstream oxygen sensor; did not go away after sensor replacement with brand-new Denso. Turned out the car still had the original 17-year old OE Panasonic battery. It was cranking fine (because it doesn't take much to crank a 3S-FE), but the system voltage would drop once running due to a couple bad cells. Other than that and a massive clump of sulfate residue around the positive terminal, there was no indicator of a bad battery (no slow-crank, nothing); replacement fixed it.

Note that ceramic O2 sensors are fragile; if it has been dropped on concrete or asphalt or similar, assume it's now bad and get a warranty return. Also keep in mind that parts store employees aren't always playing with a full deck, and might drop them during restock, or otherwise treat them roughly (have literally seen this during spark plug restock at my local NAPA, then bought 4 NGK Honda plugs an hour later and found three of them cracked or broken). For every good parts store employee, there are 50 monkeys.
 

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Fuel trims are SHORT term plus long term fuel corrections as seen on scanner.
If burning more fuel than normal could be trims are in the plus 15 range.
 
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