We have a 2013 Honda Accord that a few years back had the check engine light come on and the dealership replaced the catalytic converter under the federal warranty with a Honda part that was covered. Now two years later the light is coming on again and they are saying it's an emissions code (Code P0420) and we need to replace the exhaust pipe and muffler at a cost of $3300. Is that possible? I have never heard of the exhaust causing a check engine light. Does that make sense or could it be something else?Oh yes the dealer said the part that is the problem is the under floor converter (Part# 181505A3150) and it has an exhaust leak. Guessing a regular mechanic can replace this particular part? Or maybe at that point since the car is 10 years old (only 100k miles) we go for a full replacement of the exhaust? If so what's a guesstimate of the cost at a non-dealer?

 

Your cat should not be going bad this early unless you have a severe misfire or perhaps you have a v6 and the engine is going bad due to the VCM garbage and allowing tons of oil to get into the cat. Are there any other codes ? You should have a shop with a smoke machine do a smoke test on it to test for leaks. If you live in the northeast it's possible the exhaust system is so corroded that mechanics will not want to take on the exhaust system to just replace one part since it's going to be some work to get through the bolts if they are severely corroded. They'll just try to get you to replace it all so it's easier.

 

Okay that's very helpful. Maybe the code is (possibly) for the exhaust? Yes live in the Northeast and the tech did mention rusty bolts.

 

How much at a non-dealer is a fair cost for the full exhaust replacement btw?

 

99% sure that the underfloor converter or anything else downstream of the secondary O2 sensor will not cause a P0420.

What this code basically means- the ECU compares the values of the two O2 sensors, one before and one after the converter to determine if it's working to "clean" the exhaust as intended. If the readings are too close (both read "dirty") then it's determined that the converter is no longer working effectively.

I could imagine that things may be so badly corroded that the task of removing the old converter would make it impossible to reuse the rest of the exhaust. if that's the case, full replacement is the sensible thing to do to keep it road worthy.

$3300 installed for complete OE exhaust... is not all that wild, sadly. I would guess you could save about half the cost on the parts if an independent shop used aftermarket parts. labor may be lower too.

 

Was thinking the emission's code is bogus since the relatively new catalytic converter is passing (seemingly) clean air. We have had issues before that and have tried new gas caps and I think that caused the light to go off.. One time I had my daughter put premium in and tightened the cap and the problem went away. Should I have them replace the oxygen sensors too if I go for a new exhaust?

 

It probably needs a cat. Honda does a stored oxygen test to get to that P0420 condition. Bad sensors and exhaust leaks don't typically set a P0420 on something this modern. They have enough smarts to know if a sensor is bad vs the cat is bad.

 

This is incorrect. Honda does not use either the high or low OSC test to determine catalyst efficiency. It uses the more common switch rate ratio method.


Again some what incorrect. While a failing oxygen sensor is very unlikely to cause a false P0420 code(the criteria on that was tightened significantly around the year 2000 or so) a leaking exhaust can, and many times will, cause a false efficiency code to flag.

To the OP: unless youre burning oil,leaking coolant or driving around with a misfire occuring,it is unlikely the cat is bad and probably a leaking exhaust.

If you have a 4cyl Accord, I direct you to TSB#13-023

 

I am also have a similar problem and saw your post regarding Honda TSB #13-023. I could not find the TSB anywhere. Can you post it? Also, I saw a summary and it stated, "The MIL comes on with DTC P0420 (catalyst system efficiency below threshold). The gasket between the catalyst and exhaust pipe A may be damaged. Replace the gasket and the three self-locking nuts." Is there a way of testing the gasket to ensure its bad before I start taking it apart?

 

https://www.tsbsearch.com/Honda/13-023

 

thank you DCFIVER. Looks like my VIN is not included. Do you still think it could be the gasket? Any way to check before taking things apart?

 

It's not uncommon for a TSB to miss vin numbers. Just replace the gasket and see. You can have someone do a smoke test afterwards to test the entire system. Just make sure the car is cooled down because the cats are designed to eat up exhaust so it might not show a small leak that's there.