Posting this in case it helps somebody else down the line. I've been chasing down an intermittent P0420 code since I purchased my 05 a couple months ago. Thinking maybe this was the last straw that caused the PO to trade it in which is fine by me.
There are a whole bunch of threads on this code but it can be caused by so many different things that I figured I'd let you know how I approached it, using Techstream and some common sense. Techstream is pretty crucial for troubleshooting on this issue, otherwise you'll be flying blind.
This code basically says that the Bank 1 (driver's side) Catalytic Converter is operating below the pre-established efficiency threshold. As I understand it that can mean 3 things: 1)Cat is actually bad, huge expense 2)Post-Cat 02 sensor wonky 3)Something upstream is out of whack and giving the cat a situation that it can't deal with (running excessively rich, etc.)
Using Techstream's live engine data feed I was able to determine a couple things, and luckily I only had the Bank 1 code so I had Bank 2 as a "control" to compare against (this is key).
1. Fuel trims were consistent between banks and seemed normal
2. Pre-cat 02 sensor voltages were pretty consistent between banks
3. Bank 2 post-cat sensor was dead steady but the Bank 1 post-cat sensor was all over the place
Then, the visual inspection of the post-cat B1 sensor and replacement. I had a feeling it might be a brutal process due to rust-belt corrosion but it wasn't that bad. Both nuts that secure the sensor flange to the bung on the pipe were completely dissolved, just dust. All that remained on the studs was some remnant threading which I cleaned off using a M8x1.25 die. The sensor was actually loose in the housing and what was the old gasket for it was basically dissolved. Clearly the sensor was, itself, an air leak and my guess is that threw off the readings. I picked up the Denso sensor at Napa, it was in stock for $89 and included the gasket. With no rust, replacing the sensor would have taken 10 mins. It took me an hour to clean off the flange mating surface, upside down under the car using a mirror to check progress since the bung is at the 12:00 position on the pipe. Rust raining down onto my eyes, all that good stuff.
After replacement Techstream reported the post-cat B1 sensor voltage as dead steady and consistent with the B2 side. Pretty sure I solved the problem, but time will tell. My guess is that based on how my old sensor was so rusty that it was its own air leak, I'm not the only one who will come across this at some point.
There are a whole bunch of threads on this code but it can be caused by so many different things that I figured I'd let you know how I approached it, using Techstream and some common sense. Techstream is pretty crucial for troubleshooting on this issue, otherwise you'll be flying blind.
This code basically says that the Bank 1 (driver's side) Catalytic Converter is operating below the pre-established efficiency threshold. As I understand it that can mean 3 things: 1)Cat is actually bad, huge expense 2)Post-Cat 02 sensor wonky 3)Something upstream is out of whack and giving the cat a situation that it can't deal with (running excessively rich, etc.)
Using Techstream's live engine data feed I was able to determine a couple things, and luckily I only had the Bank 1 code so I had Bank 2 as a "control" to compare against (this is key).
1. Fuel trims were consistent between banks and seemed normal
2. Pre-cat 02 sensor voltages were pretty consistent between banks
3. Bank 2 post-cat sensor was dead steady but the Bank 1 post-cat sensor was all over the place
Then, the visual inspection of the post-cat B1 sensor and replacement. I had a feeling it might be a brutal process due to rust-belt corrosion but it wasn't that bad. Both nuts that secure the sensor flange to the bung on the pipe were completely dissolved, just dust. All that remained on the studs was some remnant threading which I cleaned off using a M8x1.25 die. The sensor was actually loose in the housing and what was the old gasket for it was basically dissolved. Clearly the sensor was, itself, an air leak and my guess is that threw off the readings. I picked up the Denso sensor at Napa, it was in stock for $89 and included the gasket. With no rust, replacing the sensor would have taken 10 mins. It took me an hour to clean off the flange mating surface, upside down under the car using a mirror to check progress since the bung is at the 12:00 position on the pipe. Rust raining down onto my eyes, all that good stuff.
After replacement Techstream reported the post-cat B1 sensor voltage as dead steady and consistent with the B2 side. Pretty sure I solved the problem, but time will tell. My guess is that based on how my old sensor was so rusty that it was its own air leak, I'm not the only one who will come across this at some point.
