Hey guys I'm new to this forum because I'm looking to ask a question to anyone out there that might know and give me some help. I bought this 2.5 4 cylinder 2013 Chevy Malibu LT a while back and it needed crankshaft position sensor replacement, which I did and fixed the code it was giving me, about 4 weeks later I get a p0420 code which is currently the issue, first, I started with replacing the O2 sensors which didn't fix the issue, then I changed the coolant temperature sensors PCV valves , which also didn't fix it. So lastly, I replaced the catalytic converter with a walker non OEM catalytic converter that I got off of RockAuto and it still isn't fixing my code, I took it to a mechanic and they told me that I needed to change the exhaust past the catalytic converter as well, which he would charge me about $800 for not including his labor fees. I didn't end up going through with that because what he said didn't really make sense to me and I've been working with my car for a while to see if I couldn't fix it myself. I took it to a muffler shop to see if maybe they knew and they gave me O2 sensor spacer for the downstream O2 sensor, they explained that non OEM catalytic converters in Chevy cars almost never work and that a lot of people put a spacer on an O2 sensor to negate that. It got rid of my p0420 code but that gave me a p0138 code which is a O2 sensor over voltage code. I asked the guys at the muffler shop about it and they said chances are the Walker cat that I put in. It might not be strong enough at all and it spacer won't help it, so they recommended that I buy an OEM catalytic converter and go from there. Now I'm planning on doing that but I want to see what everyone else thinks and maybe there's just something I'm overlooking, any other information you need just ask. thanks in advance.

 

P0420 GMC code possible causes

• Faulty Three-way Catalyst Converter Bank 1
• Exhaust Tube
• Intake Air Leaks
• Faulty Oxygen (O2) Sensor
• Faulty Fuel injector(s)
• Leaking Fuel Injector (s)
• Faulty Spark plugs
• Improper Ignition Timing
• Faulty Engine Control Module (ECM)
• Dirty Air Filter

 

Got California emissions on that car? And you don't have to be in CA either as NY or NJ require it on cars sold there as some other states also. Check the under-hood label.
Only GM cats will work properly as that's how the PCM is calibrated for those cars. Been there on aftermarket cheaper cats.