p0420 p0430?

DareDog · August 20, 2018

2005 1500 5.3 L. 135k miles. First got P0430 code, then got both 430 and 420 code. light comes back on at 220 miles. now have p0420 code and p0446 code. thinking of replacing the 02 sensors to start with. is that good place to start?

tbarn · August 20, 2018

With very rare exception, p0423/430 will need converters.

swathdiver · August 20, 2018

When the sensors go bad, they have their own codes. Your cats have gone bad. P0446 is Vent system performance, a restricted or blocked path such as from the Evap Canister filter.

DareDog · August 29, 2018

The truck seems to run fine. code came back on twice at 75 miles each time now for 0430 code. turned it off and its been close to 250 miles and no light on. I did get bottle of cataclean and ran that through it. now going to fill up with premium for a tank.

Supreme Pizza · August 29, 2018

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

https://www.obd-codes.com/p0430

I recommend reading the information in both of those links.

swathdiver · August 30, 2018

4 hours ago, DareDog said:

The truck seems to run fine. code came back on twice at 75 miles each time now for 0430 code. turned it off and its been close to 250 miles and no light on. I did get bottle of cataclean and ran that through it. now going to fill up with premium for a tank.

I nursed mine along for months, truck ran great, even drag raced it, even after light was coming on every time out. Put a new Magnaflow Y-pipe and cats on it and no more lights and mileage restored. That was the only sign that something was wrong other than the CEL, the mileage was dropping slowly but steadily.

carnau · August 30, 2018

On 8/20/2018 at 10:26 AM, DareDog said:

2005 1500 5.3 L. 135k miles. First got P0430 code, then got both 430 and 420 code. light comes back on at 220 miles. now have p0420 code and p0446 code. thinking of replacing the 02 sensors to start with. is that good place to start?

Hello Daredog. Let me see if I can give you a little information on your truck.

DTC P0420 Catalyst System Low Efficiency Bank 1
DTC P0430 Catalyst System Low Efficiency Bank 2

A P0420 and a P0430 are Catalytic converter codes. Normally this means they are getting restricted and are going to need to be replaced soon. You could check them by using a back pressure gauge if you would like. They are fairly inexpensive and easy to use. You remove the oxygen sensor before the converter and install the tool. It has a gauge that's easy to read. If it is in the red, it is bad.

The good thing about this is they are easy to change (if you have a way to life the vehicle, ramps will work fine if you don't have a lift) and they have come down in price so much over the last few years. I remember spending 1000 on a Y pipe replacement for my 2006 Avalanche.Now you can get the whole system with all the gaskets for $200! So why wouldn't you replace them? It will increase the power of your vehicle and increase your fuel mileage! I would recommend soaking the nuts, bolts and O2 sensors in a good penetrating oil like JB 80 ( https://amzn.to/2wuHPts ) It is a little more expensive then PB blaster but I believe it work 10000 times better.

Catalytic Converters - https://amzn.to/2PQc7yT

On your P0446 DTC. That's actually a totally different problem that has nothing to do with the converters.

DTC P0446 Evaporative Emission (EVAP) Vent System Performance

A P0446 is actually a performance code. It still could be a vent solenoid leaking, but this code is not a failure code for the vent. Even though I will say it is 9/10 probably a bad vent. Lol. This is another easy fix. The vent solenoid for your vehicle is located right under the frame on the drivers side. If you got out the drivers door laid down and looked under the vehicle. That's where it would be. It is very easy to replace as well. I have a video doing one on a tahoe (which is in a different spot) but will give you an idea of what is involved. Repairing this will also help with your fuel mileage by helping your vehicle not let the fuel evaporate. I will list the part you need below.

Vent solenoid - https://amzn.to/2N3l0Xj

I hope this helps, And if you need anything else just quote something on here and I will get back to you asap.

carnau · August 30, 2018

Like I said this is on a Tahoe but will give you an idea of what you're going to have to do.

DareDog · September 28, 2018

So are the cats finally bad? Now CEL comes on after sitting idling at a stop light. Both codes. Tired the cat cleaner and light went off for 600 miles before came back on.

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DareDog · November 5, 2018

Update on this. Put o2 extender on it. Now Got a o2 sensor code instead of the normal 430 code. Just put a new o2 sensor in it today. Hopefully that fixes it.

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sempersteelers_43 · November 8, 2018

I started noticing the same thing on my 08 Silverado 5.3 about a year ago. Ran the codes and got p0420/p0430 and tried to replace just the oxygen sensors, but that did nothing to solve the issue. Next step will be to replace the Cats and see what happens, but dealer wanted $1500 just for the part. Still looking around for a more economical solution, but want to get something that will be a step up from OE. Cheapest I found was from a local place (Allied Exhaust Systems) for about $500. Keep us posted on your solution.

sefiroxx · November 8, 2018

When researching cat replacements, be careful of cheaper cats as they likely have less palladium/rhodium on the coating.

Also, no guarantees, but consider if the mfg provides a California version of the cat. CA requires an extended warranty period. A cat would have to be better constructed and more metals to withstand lumber period. For some mfg, they use the same cat as other 49 states, but charge more in order to backfill the insurance to cover the replacement. They would have to have confidence in the product to warranty it in CA.

swathdiver · November 10, 2018

On 11/4/2018 at 9:23 PM, DareDog said:

Update on this. Put o2 extender on it. Now Got a o2 sensor code instead of the normal 430 code. Just put a new o2 sensor in it today. Hopefully that fixes it.

No, I think you just kicked the can down the road, tricked the computer but the cat is still bad.

DareDog · November 10, 2018

No, I think you just kicked the can down the road, tricked the computer but the cat is still bad.

if it is plugged wouldn’t it be down on power? Or I could hear that it is bad?

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swathdiver · November 11, 2018

4 hours ago, DareDog said:

if it is plugged wouldn’t it be down on power? Or I could hear that it is bad?

You cannot always hear a bad cat, they don't all fall apart and rattle around. Yes, you would be down on power some but could you feel it? I couldn't, even raced my truck at the track and still ran decent times. Besides the code popping up, the only other tell-tale signs were the drop in gas mileage and watching O2 sensors on Tech2..