Code 0421

eddieammerman said:

Check engine light came on code 0420. I read the posts about rear cat clogged or 02 sensors. Decided on replacing sensors. Do I need to replace upper and downstream sensors or just downstream also is this the one's on the passenger side?

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Sabertooth^2 said:

Generally it's a downstream sensor, or plugged cat on the manifold. Rear cat isn't monitored

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Sabertooth^2 said:

Cylinders 1 and 4 are bank 1, they meet on the passenger side.

Cheaper is to swap your downstream sensors left/right and see if the code moves. You must physically swap them and plug them in on the appropriate sides. Just changing plugs or just changing location will cause issues. If it does, it's a bad sensor. If it doesn't, it's a bad cat.

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dcspider said:

I will help on this thread because is a new issue I am having. (You Guys are in luck!).

If you don't who I am, well I was the crazy guy that tried to keep his car as close to stock as I possibly can as an experiment and to help figure out future issues for this forum. That said the time of my car been stock 100% has sailed long away.

YES FIRST REPLACE THE SENSORS! CHEAP ISSUE FIRST AND THEY ARE EASY TO BREAK. THAT SAID!

The catalytic converters on this vehicle are not great. the sensors are not going bad because they are reading wrong, especially around the first 100K.

Magnaflow makes a great swap kit, Or if you are technical like me I say build your own. Have fun kids.

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eddieammerman said:

Thanks dcspyder but I have a 2.4.

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