P0420 repair ecm wiring.

[PastorRiverofL]

Hi everyone,

I'm new on this forum and I need help please on my 2000 Chevy Tahoe. It has a P0420 code on it and the check engine light is on, but I was told to check the ecm engine control module. The problem is I cannot locate let alone know where to find the ecm. I was also told to check the wiring for the ecm, can someone please help with this problem, thank you and God bless!!!

Need help.

 

[sumo]

P0420 is a catalyst below threshold/efficiency code. There are a few things that could cause this or a combination of. You have a 02 sensor before the cat and after the cat on each side. It's throwing that code because the pcm is not reading the specific value after the cat.
You could have a clogged cat, bad 02 or maybe even both.

 

[Rocket Man]

This ^^^^^^ I'm betting on the cat.

 

[jaywoo65]

P0420 is more specifically for the drivers side after cat sensor. If you are into a little wrenching, the easiest thing to do would be to swap the passenger side after cat O2 sensor and the driver's side sensor. Take it to autozone and have them clear the code(unless you can do it of course). If it comes back as a P0430 (Bank 2 sensor) you know it's a bad O2 sensor. If it comes back as a P0420, you most likely have a bad cat.

 

[rockola1971]

Your PCM--Powertrain control module which controls engine AND transmission (they havent called them ECMs in decades) The ECMs back in those days only controlled the engine.

Your post cat O2 sensors only purpose in life is to "monitor" the cats. The pre cat O2 sensors purpose in life is to measure the O2 in the exhaust which is used to determine lean/rich conditions and the PCM uses that info to regulate the fuel injection to lean or enrichen the fuel/air mixture in cylinders to get a target value programmed in the PCM for any given load/RPM/Throttle Position.
You sure you dont have any other codes?

Have a look here for some ideas of cause: https://www.obd-codes.com/p0420

 

[Rocket Man]

BTW your vehicle has a PCM , powertrain control module which controls both the transmission and engine. ECM's are found in later model vehicles. Beginning with the NNBS (07-14) for instance GM separated the transmission computer from the engine computers so they have an Engine Control Module (ECM) as well as a Transmission Control Module (TCM). Beware of people who would say otherwise. Lmao.

 

[LastGas]

Or... it might not have anything to do with the O2 sensors or the cat converter.
It could be related to incorrect fuel air mixture, such as when there is an air leak between the throttle body and the MAF (mass airflow sensor). A loose hose clamp could be the culprit.