2003 Yukon Problem

[Nyjetfan21]

So here I am again I finally got a chance to purchase a better oxygen sensor and cleared the code and now the engine light came back after driving about 3 miles. The new code is PO420. Here is a pic of the scan. Any help is greatly appreciated.

 

[HiHoeSilver]

So here I am again I finally got a chance to purchase a better oxygen sensor and cleared the code and now the engine light came back after driving about 3 miles. The new code is PO420. Here is a pic of the scan. Any help is greatly appreciated.

View attachment 228199

Ok. This code is triggered by the downstream o2 sensor on the driver side. So.... kind of the same steps we took for the other ones. You can:

Check some live data on that sensor.
Inspect wiring to the sensor.
Swap driver side to passenger and see if the code goes to bank 2.
Replace it.
If the sensor passes all checks, or is replaced by a quality one and the code reoccurs...sorry to say that you're likely looking at new cats.

@SnowDrifter concur?

 

[Nyjetfan21]

Before I go through all of that do you think if I Purchased a catalytic converter additive cleaner from my local auto parts store would that work a friend of mine told me I should give that a try or would I be wasting my time

 

[mikeyss]

I kinda remember a few years back in my old 05 Tahoe I had to replace the passenger side upstream o2 sensor. I still worked at the dealer at the time and I think there is a bulletin that you have to do an update to the computer, something about new calibrations. This was years ago so I may not be remembering correctly, but maybe this could be your issue too.

 

[Nyjetfan21]

Would an additive cat cleaner be worth trying or is it a waste of time

 

[HiHoeSilver]

I kinda remember a few years back in my old 05 Tahoe I had to replace the passenger side upstream o2 sensor. I still worked at the dealer at the time and I think there is a bulletin that you have to do an update to the computer, something about new calibrations. This was years ago so I may not be remembering correctly, but maybe this could be your issue too.

Never heard of this. Interesting.

 

[HiHoeSilver]

Would an additive cat cleaner be worth trying or is it a waste of time

I can't speak directly to this, but there are definitely additives that can do what they claim for a number of purposes.

 

[SnowDrifter]

Ok. This code is triggered by the downstream o2 sensor on the driver side. So.... kind of the same steps we took for the other ones. You can:

Check some live data on that sensor.
Inspect wiring to the sensor.
Swap driver side to passenger and see if the code goes to bank 2.
Replace it.
If the sensor passes all checks, or is replaced by a quality one and the code reoccurs...sorry to say that you're likely looking at new cats.

@SnowDrifter concur?

Concurred

Would an additive cat cleaner be worth trying or is it a waste of time

Waste of time IMO

cat cleaner would only be effective if it's Crossley soaked in oil or something and causing it not to light off. In which case, it would just get soaked again because mechanical problem

Worn away platinum coating wouldn't be replenished

Mechanical damage due to internal breakage or melting from running rich / lean won't be fixed


If there is some sort of no combustible ash or ceramic deposit on there from oil additives or something, a cat cleaner won't be able to dissolve or remove either of those

So yeah I wouldn't bother with the stuff.

 

[TheAutumnWind]

Would an additive cat cleaner be worth trying or is it a waste of time

waste of tim/money as quick fix magic additives often are.

 

[merlin1128]

I know this is an old post and one thing I learned from my mechanic is when you are having multiple problems check all your ground wires on the frame. I had the same thing happen to me which started out simple with the one under the front on the frame losing its ground slowly. My rear wiper was possessed and on super hot days in my garage starting up and pulling out it would just go on by itself with the switch off. I had to open and close the rear hatch window to get it back to the park position to stop it. this continued intermittently then I got tighten fuel cap with it, which I know was tight. Then with this going on the next thing was the air bag light went on with a message on the dash. Turning it off and restarting got it to stop, but still continued intermittently. Then one day everything started showing up on the dash... Check Engine Light, ABS, and who knows what else due to the Tahoe was popping messages and lights on the dash like no tomorrow.

Then I remembered what he told me a long time back when you start to get all kinds of stuff like this "Check Your Ground Wires" because current will follow the path or least resistance and if one thing is using whatever ground is left connecting to the frame other things will play havoc. I did just that and not sure if this is your problem, but it starts out slow as the ground is starting to be gone. That how could all these things be going wrong and then more and more.

He also told me this is something a lot of mechanics miss due to they are always reading codes off the computer with their scan tool. That the reason they are popping these codes is they do not have a good ground to the frame. Which I believe there are 3 on the Tahoe the one from the battery going down in front and then two more on the drivers side under the door bolted on too.

Did just that and guess what? The ground on the frame in the front was slowly coming off with the bolt rusting away and the ground fell off and this is the one that comes off the battery negative just hanging there.

It was a simple get out the Dremel tool and clean all that rust off the frame for a nice new contact and a stainless steel bolt to put it back on, then sprayed it with some truck bed spray to seal it up and did the same with the others.

All lights and messages instantly gone and I wondered why my fuel mileage was getting worse and that was part of just a simple ground going bad and falling off.

I decided to take a ride by him to have him put his scan tool on it to see what it showed and WOW did it have codes galore all from this. He cleared them all and said drive it for a while and said that was it for sure, but come back in a week and lets scan it again and when he did no codes at all showed up.