I have a 2007 TL-S with 116,800 miles and have been battling P0420 (Bank 1 Below Threshold) for a while. The check engine light appeared for the first time in June but only stayed on only 2 days. It reared its ugly head again last week stayed on for a day, disappeared the next morning, and now its back again.


I'm going to have a mechanic look at it this weekend. My question: If it turns out to be a bad CAT can I replace it with a XLR8 J-Pipe to resolve the issue?

This one below:
http://store.excelerateperformance.c.../i-236895.aspx

Thanks in advance for any help you guys can provide!

 

no. the jpipe has nothing to do with the cats. you have 2 primary cats. one bolted to each cylinder head. bank 1 would be the cat closest to the firewall. it could be a bad cat or a bad secondary 02 sensor. Your mechanic can run some tests to figure out which one it is

 

Oh! that's the weed code.


time to light up!

 

it'll temporarily fix your problems!!

 

Usually the P0420 is, like others have mentioned, a bad catalytic converter. It would be the cat at the rear of the engine next to the firewall. A good test would be to take an electronic laser thermometer and to test for a temperature difference between the inlet (top) and outlet (bottom) of the cat. Do you smell rotten eggs around the exhaust frequently? This usually indicates a bad catalytic converter if mixed with other symptoms (codes and such). In the past, I have noticed that some aftermarket catalytic converters may temporarily fix the problem or not last. Go with the OEM Honda unit, and no it is not that much more expensive if you find a good vendor from this website. BTW, I believe one of the driveshafts has to be removed to take it out. Best of luck.

 

It's going to be the cat. The code doesn't necessarily mean it needs to be replaced... I had an exhaust shop install a defouler/spacer on the O2 sensor and I haven't seen the CEL in months. It seems to be common on our cars for the rear cat to lose efficiency.

 

I can +1 on the defouler. Got mine from HeelToe Automotive. Shipping was quick and the product worked.