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Discussion Starter · #1 ·
Hi Folks,

Me again, with some post-rebuild questions. I just finished my engine and trans rebuild, and my first full driving day (100+ deg, stop and go), I got a P0151 and P0420. The 0151 means right hand side, forward o2 sensor, right? And the P0420 means left side catalyst? So I have problems on both left and right side it seems?

I would assume having those codes would prevent me from passing emissions testing too?

Thanks for your input!
 

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Discussion Starter · #2 ·
It turns out I had a few issues. The P0151 was O2 sensor bank 2, sensor 1 circuit low. That's the front sensor on the right hand (passenger) side. Also, the P0420, which is catalyst efficiency bank 1, or left hand (driver) side. This didn't make any sense to me. Why would I have a low voltage on bank 1, and a bad catalyst on bank 2? The attached screenshot shows the culprit. The first pic is bank 2 and the second is bank 1. That readout is supposed to look like bank 2. In other words, the first sensor is reading rich and lean all over the place, and after the cat (sensor 2) is supposed to be more or less level.

So, bank 2 was looking good, bank 1 was no good at all, it looks like a bad catalytic converter. Another 500 bucks at least. But what still didn't make sense to me is why I had codes for BOTH sides. Usually, it's going to be one or the other, especially with waveforms like I had. That bank 2 looked perfectly fine. Scratching my head.

I decided to go "back to basics" and double check my work. I thought all 4 of those sensors had different connectors. It felt like that when I put em in. The front 2 may have different connectors, I don't know, but what I did find is that the back 2 do indeed have the same connectors. They're supposed to be idiot proof because one sensor's lead is supposed to be longer than the other, and you're not supposed to be able to screw it up. Both my sensors had the 18" leads, so ... it's possible to put the B2S2 sensor to the B2S1 connector. Which is exactly what I did. I didn't know that for sure until I started pulling one connector at a time and got codes for the "wrong" bank!

So, I went and got 2 new rear sensors, and connected them properly this time. I drove it for an hour and got no codes. I didn't check my voltage levels after the new parts were put in, but those codes popped up within 10 or 15 mins of driving before, so I'm certain I'm good. I probably could have just swapped connectors and been fine, but I wanted to be sure. This is a new build and I want to pass emissions. I still don't have a clear explanation for the P0151, but it went away. Maybe it just didn't play nice with B1S2.
 

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