Bank1 O2 sensor reading.....

I have an 01 Extracab Tacoma that has an issue resulting in a check engine light. I keep getting a P0420 code which I was told could be the front o2 sensor or the Cat Conv. When looking at my live data, I see the front sensor is reading 0.00 and the rear sensor varies around .3 or .4. What is the front sensor supposed to read? I checked my daughters car for reference and hers showed a slightly higher number for the front sensor compared to the rear. I just don't want to spend unnecessary money.

 

Front sensor should be around 3.3 I believe. Rear sensor between .1 and .9 depending on cruise vs accelerating.

I'm going off memory and could be off...so hopefully someone can verify.


Edit: You can get a new Denso sensor from Rock Auto or Amazon for reasonable. Check to make sure you don't have any leaks, especially around gaskets.

 

Front sensor should be the one bouncing from .1 to .9 cuz its going from rich to lean rich to lean trying keep afr in the sweet spot. Rear should be pretty much flat. If rear is fluctuating your cat is most likely bad.

 

I really recommend a YouTube channel called Schrodinger's Box.

Lots of pertinent info.
https://m.youtube.com/#/user/mattshadetree

 

They are about $110 for an upstream sensor and should be replaced every 75-90k miles anyways.

I just replaced both up and downstream sensors and it made a world of difference on the trucks mpg and performance, I was not throwing a code though.

$170 Denso 234-9003 Air Fuel Ratio Sensor

http://www.amazon.com/gp/product/B000C5UFU8?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00

 

More than likely it is the upstream, it is the one most apt to fail....if you shop Amazon, Ebay or RockAuto you get the best pricing, make sure to get a Denso, that is OEM, any other brand and you may have problems...

I just changed mine, I wasn't getting bad mileage, but kept getting a PO420 code, so I changed it out (very EZ to do) and no problems since...try the front O2 first, it is the most likely suspect in these trucks...

 

I'd diagnose a failure before replacing. But hey, that's my money.

 

Sorry but that is incorrect.

Only a factory mode scanner (something higher end) will be able to read direct voltage, or using an oscilloscope. Any wideband sensor like this will always operate within .25V to .45V, as they typically have a 0.5V reference. You are reading the voltage drop from between the reference and sensor cell, not actual sensor voltage. Its still doing the lean/rich waveform, but its all internal to the sensor. A brand new sensor will operate in the same way.

 

There is no set service interval for the A/F sensor, their operation falling out of range is the indicator, it wont always throw a CEL.

 

See that's what I've tried to do and although I didn't fully check the ohms readings and whatnot as I got confused, mine SEEM to be working properly according to live data. And I've been waiting for answers such as others have stated saying that even though they weren't throwing codes, or were at least throwing the p0420 code, and replaced the FRONT sensor, that it made a change and no more code... I'm wanting to suspect my front sensor is the cause of decreased performance and mileage, but didn't wanna spend the money when I wasn't 100% sure that was the cause and because I have quite a long list of other maintenance items that need tending to with a limited budget. I was convinced my dual cats were clogged. But after install of whole new system from y pipe back with a high flow cat, I still get code and I didn't really notice any gains at all. I realize there won't be a huge gain with that but paired with cai and the fact I thought cats were bad, I expected to see/feel SOME kind of gain in performance/mileage. But there seems to be NO change after I installed the system. Not in mileage or anything...

 

for $100 I was fine with replacing it since the last time it was done was 110k on the clock in july 2009.

 

OP, please check out the following.
https://www.tacomaworld.com/threads/bound-to-happen-i-finally-got-my-first-p0420-code.326408/

Our trucks are eventually going to throw P0420 for one reason or another. My CEL is on right now for one. Its simply a catalyst efficiently warning, usually a sign of a old catalytic. I drove the truck hard until it turned off then went in for a smog check a few months ago, passed fine.