So I've had a check engine light on my 03 HCH for a while, and it's been the p0420 code. My state doesn't do inspections so I don't really care, but I don't want the check engine light on. I decided to space the o2 sensor and clear the code hoping that this would solve my problem. Much to my surprise, it did not. My questions are these: (1) Does the car adjust fueling based on the rear o2 sensor, or is this solely to measure the efficiency of the catalytic converter? (2) Will the car throw a code only if the catalytic converter is letting too many particles through, or will it throw the code if it's clogged as well? (3) Can the code be thrown if there is a problem with the actual o2 sensor? I fully believe that the catalytic converter is bad, but I can't believe that the spacer didn't fix it, which is the only reason I'm thinking it's possible the o2 sensor is bad as well. Thanks for any help!

 

Cat system below threshold, Bank 1. I had the same code checked yesterday at Advance Auto.

 

Think about what you did for a minute. The P0420 code is set when the convertor is operating below minimums (not converting CO and Nitrous oxides to water vapor and H2O. You replaced a non working convertor with a non working spacer pipe and you expected it to somehow magically fix itself?

Put a convertor on the car and clear the code if the is the ONLY code that was thrown and if you don't mind taking a little risk. If you want to eliminate the risk of not fixing it by replacing the convertor only, there are procedural tests to verify and find out a few other problems that might throw that code before replacing the convertor. You will need a shop manual and some diagnostic tools for those tests.

 

Not to be a jerk, but you obviously didn't read my post.

I think you're confused about what I did. I spaced just the o2 sensor. This is a really common "fix" for bad catalytic converters. I don't care even the slightest bit about the amount of emissions the car is producing, I just don't want the check engine light. If you space the o2 sensor so it is farther from the exhaust stream it will usually read lower levels of emissions.

 

That is a heated sensor, once you are out of a closed loop on O2 circuit (up to temp), you sensor will keep dropping below temp due to being out of the exhaust stream and still set a code. Why not just fix it right and be done with it? Your P0420 code indicates the upstream catalytic convertor is bad (combined with the exhaust manifold) and they would run about $300 to $325 plus about 1 to 2 hours of your time to correct the problem.

By the way, that code WILL affect your short and long term fuel trims as well as the timing on the engine as the system thinks it is running too rich. If it leans out too much trying to correct the issue, you can wind up with a hole burned into the top of the pistons.

Your money, your choice......