Looking for some advice. My 2009 HHR 2.2L had P0420 and P0010 codes with check engine light on. Replacement of cam sensors fixed P0010 but replacement of Catalytic converter and both oxygen sensors seems to not have addressed the P0420 code. I have tried repeatedly to erase it but I cannot get if fully erased with my scanner. The code was in my scanner a number of times and I could erase all but the final one. I noted the engine will not rev over 4,000 rpm so I assume it is in limp mode. I will admit the car has 132,000 miles on it so I bought a converter and oxygen sensors on Amazon to save some dollars. The car has run for 15 minutes now since changing sensors and cat and actually the check engine light is not on, but the scan tool still reads P0420 code and I cannot rev engine over 4,000 rpm. I'm not sure where to turn next and can't seem to find anything on YouTube that targets the limp mode issue also. Any suggestions before I have to break down and take it to a dealer? Thanks in advance

 

Welcome to the site, if you’re not getting a CEL, try a battery lobotomy, disconnect only the negative cable at the battery for 15 minutes, then reconnect it, this will reboot the computer in the car.
check the coolant level and the engine coolant temperature sender.

https://www.obd-codes.com/p0420

 

Is the P0420 current, pending or historic? If historic it will stay for 100 cold starts and is just information. If the CEL is off, relax.
Do you mean it won't rev over 4,000 while in park? That is the rev limiter in the computer; i.e.: normal.

 

Thanks to all for the responses. Yes you are correct .... it is historic and I just disconnect battery for 2 hours and as soon as reconnected the 0420 code still there but what you sat makes complete sense. I did start it on the hoist and CEL is not on and no other codes. Yes it is in park when I am revving it so what you say I did not know either. I will take it for a drive in a short while as I need to also put together his left rear door first. I had it apart for a door actuator. Grandpa is trying to help him out and save some costs as he's only 17 and this is his first car. I'll let you know what I find when I drive it shortly. Thanks again!!

 

All seems to be good right now. Just drove it 25 miles and no CEL and engine revs up to red line. Fingers crossed and only more miles will tell but hopefully all is fixed and in a few weeks I'll check to see if the P0420 is out of permanent status and gone. Thanks guys for all the advice!!!

 

Double check your coolant level under the pressure cap in the upper rad hose , there shouldn’t be any air space .

 

Permanent is the same as historic.

 

Thanks alot for all the info. So far it's running great!

 

Did you check the coolant??

 

Thanks for asking...yes I did. It needed a slight top up and added some to the coolant tank also.