I replaced the catalytic and flex pipe on a 2008 HHR with NAPA part, now have "CATALYST ERROR" code

What exact code number is it giving and was the tubing and cat you installed the same inside diameter as the stock setup?

Sorry, it's my son's car and he can't remember the number, but the description was "Catalyst Error". Pipe size is same, NAPA replacement pipe has 1 catalyst and OEM has two catalyst. Dealer said it has to have two to reduce flow. Did I get the wrong part from NAPA?

When I try to look the part up on NAPA's site there are no parts found. So I have no clue what part they sold you. The exhaust diagram I found only show a single cat setup. There is a resonator after the cat they dealer could be mistaken for a second cat by the dealer though.

Found the code: PO420 "Catalyst System Low Efficiency. Only dealer has the right part.

After finally locating a factory diagram I found the OEM part number. That model with the 2.2 does use a two cat system with the o2 sensors before and after the first one. I imagine the single cat is affecting the flow to the second sensor making the computer think the cat is bad. I did find an oem pipe at a dealer online for around $500 if the dealer wants to much to replace it.

I'm an electrical guy, my question on the 2nd sensor is, can I add a resistor to change the voltage to the circuit to fool the computer in thinking all is well? and if yes, do you know what the resistance would be?

ive read about people doing/attempting it. im unsure if its possible or not. you would need to do some searching online to see how to people have tried it in the past.

eastern converter company makes an eco gm replacement for the hhr, you dont have to go to the dealer

part number is 50459

I replaced my front Cat. with an aftermarket cat and immediatly noticed that I had a ton more exhaust coming from my tailpipe. "It blows like crazy now!" I also increased my MPG by 1.5 so that is wonderful. Anyways the new Cat that I bought has less restriction on the flow so now my check engine light comes up with the same as yours the 0420 its saying that there is something wrong with possibly the cat, but most aftermarket cats you buy arent the exact same GM part thus having a different airflow through the cat. My Cat was even a bolt on but was still different design. However, you should really take time and read the article on this link before changing your cat again. I can guarentee this is the best fix for you!! Feel free to call me at 316-409-4838 I can talk to you about it if you'd like! http://www.s10forum.com/forum/f89/do-it-yourself-o2-simulator-126774/ and this option if you want to spend a bit more... but is probably not neccessary... http://www.ubertechnics.com/O2_Simulator_2.5.aspx The first link is more or less just a mechanical fix for this.. It holds the O2 sensor farther from the exhaust pipe and exhaust gases. Therefore the 02 sensor tricks the computer will be tricked into thinking that the cat converter is working because of the absence of non-treated exhaust gases! And the second fix is more litterally tricking the computer only. ..

STILL NO ANSWER 1ST OFF IF YOU HAVE MANUAL TRANS. ALL YOU NEED IS ONE CAT #50374.BUT IF YOU HAVE AUTO TRANS YOUR CAR NEED TWO CATS. I HAVE A AUTO TRANS. AND USED NEW CAT FROM EASTERN #50549 AN STILL GET CODE 420 ANYONE HAVE A GOOD ANSWER.. PLEASE HELP TOM