O2 sensor code

Had the converters stolen and a local shop replaced with ca compliant ones as well as the downstream o2 sensors with napa replacements.

now there is a o2 sensor code. Not sure if it’s the non oem cats or o2 sensor or ??

also, on a side note, would love to find a set of 4 oem cats if anyone has a set!

 

OP, Posting the actual codes would be helpful to your cause...

 

It’s a P1057

thanks for helping!

 

Please confirm P0157 vs P1057... the later is not related to CAT replacement.

 

Ah good catch. It is p0157.

 

So, that code seems to indicate low voltage return from the O2 sensor over a prescribed timeframe.

In O2 sensor world, low voltage means lots of O2 and high voltage means very little O2. If the voltage is going (and staying) low, then the sensor THINKS that it's seeing excess oxygen.

As a start, I'd humbly recommend checking for exhaust leaks. If there is a leak at the flange (or a poor quality weld) not only does exhaust get out, but air gets in.

If that checks out (i.e. no leaks), I'd recommend getting a scan tool and watching the live data coming from each sensor. That will tell you more about what's going on. For example, the upstream sensors should read a sinusoidal wave as the truck's computer varies the fuel trim. Downstream will be much flatter response (no waves) when the cat warms up and does its job.

 

@jfryjfry

Not sure if you've resolved your issue yet, but I went back and grabbed some screen captures from when I had a similar error on an SC430 we have. It was showing a code P0430 (different code than yours, yes) which is catalyst efficiency. In our case, that resulted in a long-term low voltage on the downstream O2 sensor on that bank. That low voltage is what made me think it might be related to what you are seeing. See the screen capture below.

 

In that previous post, the red line is the pre-cat O2 sensor. It's wiggling as the car tries to vary the air/fuel mix to get it right. Note that the after cat sensor is flatter (which it should be), but stays near zero. That means it's lean (too much air). In my case, a small pinhole leak in the pipe (from rust) was allowing it to suck in air.

Below, is the other bank that was peforming normally. Note that the before O2 sensor is still a sine wave, and the after cat O2 sensor is still pretty flat, but it comes up from baseline to the "desired" O2 reading and stays as the cat heats up.

In short, if you can get a closer look at what your O2 sensors are doing real-time, it might help determine the issue. If BOTH lines go sinusoidal and wavy (before and after), it usually means that the cat itself is shot.