Oxygen sensors failure

1st time posting - my 2012 just threw a CEL at 36,900 miles = lean fuel mixture. The dealer says both oxygen sensors need to be replaced. Anyone have any information/theories as to why both sensors would fail? Truthfully I've never been thrilled with the way the engine runs in general. There's quite a bit of hesitation & knocking & it's been that way since day 1.

 

Has it been in to them since "day 1" when it was knocking and sluggish?

A paper trail is a good thing to have on your side.

These trucks are pretty quick IMHO, so something's been off for a long time with urs.

What have u done to it so far?

Air filters, exhaust, intakes? Anything?

What grade of gas do u run?

 

Typically these trucks also run richer than Bill Gates

 

I use Mobil 1/MOA & 93 octane. I found that 93 octane greatly reduces the tick/knocking upon acceleration. I just can't wrap my head around both oxygen sensors failing at the same time. I haven't made any modifications since I bought it.

 

Fuel trim is read and controlled by the A/F sensor in the front. The rear sensor's job is to simply monitor the efficiency of the cat. Don't see how a bad rear sensor would have ANYTHING to do with performance.

 

Oxygen sensors are always replaced in pairs. It's because the new one will read differently than the old one that's in there and throw the computer off by telling it one bank is running richer or leaner than the other. Auto mechanics 101: replace oxygen sensors in pairs.

 

I dont think its the Cat because of how new the truck is but if the problem isnt fixed with the sensors you better make sure they replace it under warranty, IDK what the rules are in virginia but where I live you have to get the factory cat (which is about 2500 not including labor) just to keep it legal.

The only reason I think it could be is cause the same happened to my old truck but I ran it to the ground like that.

 

It is a common problem on ALL Toyota 6 band O2 sensors. It sounds like you have had a bad sensor since day one, one reads rich and leans the truck out. This is usually caused by a fouled plug over a long period, generally a broken electrode on the plug causing poor spark. Replacing the sensors is not an issue and who does the work should be directly relevant to your powertrain warranty. My 05 cost me $200 for both and i changed them in 20 minutes. The plugs were slightly more...

 

Not true. You only replace a part if it is defective. I only replace the ones that are bad. As a auto repair shop, one would be doing their customer wrong by replacing a part that is not defective, thus overcharging them. As expensive as an O2 sensor is, there is no need to replace both unless they both are bad. What needs to be done is a proper diagnosis and an answer to the OP from the dealership as to WHY they say both sensors need to be replaced. I would say that 95% of the time if you get a lean code and BOTH sensors are reading lean, you have a different problem. It is rare for both to fail at same time (but not unheard of obviously) I am not sure where you went to take your Auto Mechanics 101 class, but I would ask for my money back. (This is being said sarcastically, and in jest)

What can be confusing is why they said both oxygen sensors need replacement for a lean condition. If there is a lean condition, then the sensors are doing what they are supposed to be doing: Telling you the A/F ratio is lean. The key would be to run the engine off-idle and see what the A/F sensors are reading (I call them A/F sensors because Toyota does not actually USE oxygen sensors to monitor fuel trim in the traditional sense. They use A/F sensors for that, which measure the exhaust totally different.)

OP, I would be curious what the fuel trim is at? Are we talking 10% decrease requested? 15%? 20%? Did they verify fuel pressure? I would be asking more questions if they said I needed to replace BOTH of the sensors.