djpinoy

Hi all - I've got a 2004 TSX w/ 176K miles. Over the past couple years, I've intermittently gotten a Check Engine Light (CEL), which reads out the P0420 Diagnostic Trouble Code (DTC) when connecting to the OBDII port. As many of you know P0420 is "Catalyst System Efficiency Below Threshold (Bank 1)" which will fail me out of my fast approaching emissions test

I've done some homework and read lots of threads with all sorts of tips and suggestions: making sure to use Top Tier gas, inducing Seafoam directly into the engine to clean out the exhaust, changing out the spark plugs, installing a defouler, and even a YouTube video about adding lacquer thinner directly into the gas tank to clean out a clogged cat (is that really safe?)

My issue is more about diagnosing the source of the problem as at ~11 years and 176K miles, it might be possible that the cat is bad. To dig in, I used the Torque Android app to try to take a closer look.

As I would expect, the Torque app shows:
* Emissions Test for Catalyst marked as "Complete"
* DTC shows P0420 "Catalyst System Efficiency Below Threshold (Bank 1)"
* Mode $06 Test Results:
- TID:$62 CID:$04
- Max: 2,640
- Test result value: 2,891
- FAIL

From here, I try to take a look at the raw O2 sensor data (also in the Torque app) and I notice that while there's a graph for "Bank 1, Sensor 2", there's no data when I select "Bank 1, Sensor 1". My assumption for the 2004 TSX is that there are two sensors: One before the cat (Sensor 1) and one after the cat (Sensor 2), and then if the difference between the two is too low, then I fail emissions.

Questions:
* Should I be seeing data for "Bank 1, Sensor 1"?
* If there IS supposed to be data from "Bank 1, Sensor 1" (but no data is coming out), could this be the reason why it's throwing P0420? Or would it throw an O2 sensor code instead?
* Assuming it's the cat, any other tricks to pass emissions short of replacing it?


Thanks in advance!

TexasHonda

Primary (upstream of converter) sensor is an air/fuel sensor and output is different from an oxygen sensor. Equivalence ratio may be what is output from A/F sensor (by ECM) to your Torque app. It is a ratio that should be near 1 if A/F sensor is working OK. Since you don't have a code for A/F sensor, it is likely working correctly.

Bank 1/Sensor 2 is an O2 sensor and will output a voltage signal. If this signal oscillates between low (0.1-.2 V) to high (0.7-0.9V) w/ a frequency of 1-2 per second at idle, then cause for P0420 is confirmed.

You can check for exhaust leaks which can sometimes cause P0420, otherwise a new converter is likely needed.

good luck

netsx04

What happened with your car and the dreaded P0420 code? I have ~193k on my car and P0420 started popping up on my car. I reset the CEL, but it came back 500 miles later. I replaced the A/F sensor at 170k so I suppose it's possible that whatever destroyed the original A/F sensor is damaging the catalytic converter. I thought I heard an intermittent air leak, but not sure...
Also been using the Torque App and OBD reader. The A/F sensor typically runs 12-16, but jumps to 29:1. Is this normal?

netsx04

Anybody? I also have a pending state inspection...
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