P0420 Bank 1 Code Check Engine Light

Good afternoon,

You need a catalytic converter for bank 1. The code indicates the precious metals inside the catalytic converter are worn out.

I attached a picture of the location and the part from rock auto.

Roy

Hello,

Direct Trouble Code (DTC) P0420 is simply stating that catalytic converter, through normal wear and tear, isn't catalyzing as it should be, and needs to be replaced. Your vehicle has two Oxygen Sensors (O2) per exhaust stream, so 4 cylinders have 2, and V6's and V8's have 4 total. Each exhaust stream has an upstream and downstream O2 sensors, the upstream maintains the engines Air:Fuel ratio and the downstream O2 sensor monitors the catalytic converter for efficiency. If you wish to replace the catalytic converter we can give you step by step directions on how to do this. Please let us know.

Thanks,
Alex
2CarPros

Okay, you need to raise the car.

If you looked at the picture I sent, there are 3 attaching points that need to be released. There is one bracket that has to be released as well.

The front bottom is easy to release as it is right there. The one that attaches to the rear exhaust is the tough one. There are 2 bolts that hold it up securely.

The rear part has 2 spring bolts. They will have to be replaced when you take them off.

Spray rust remover on all connections before attempting to remove the bolts.

It should take you about 1 to 2 hours. When you have it down, you will need to remove the O2 sensor. It will be easier when it is on the ground.

Roy

You are welcome.

We are always glad to help.

Roy

With the trims on the lean side I would suspect a faulty Air Fuel Ratio sensor (upstream oxygen sensor) If you can attach the freeze frame data I would love to see bank1 sensor 2 data. If it is almost flat lining to zero then I recommend you replace the upstream sensor.

The downstream sensor should read around.450 volts. If it is varying. That indicates a bad catalytic converter. The upstream will rarely set a 420 code unless you have a gross exhaust leak.

Roy

I just did one recently. I replaced the catalytic converter almost a year ago and came back with the same code. When I saw the freeze frame data the rear oxygen sensor was close to 0 volts. But I also noticed the fuel trims were high on the lean side but not high enough to set a running lean fault.

I replaced the rear oxygen sensor thinking it was just flat lining and road test and catalyst monitor test results barely passed, and what do you know. Comes back again with same catalyst code. Freeze frame you see the rear sensor close to zero. Fuel trims a little high on the lean side but not high enough to set the check engine light. So I replaced the air fuel ratio sensor. Road test it, set catalyst monitor and test results were way higher. Vehicle has not returned since.