02 Yukon Denali PO420 Code

[Redfire Metallic]

Anybody have any suggestions as to what it could be??

 

[OR VietVet]

That's your bank 1, cylinder 1 side, cat efficiency. Likely have a catalytic converter going bad or oxygen sensors problems. How old is the cats and sensors?

 

[PNWYukon]

I had a similar issue and it was bank 1 sensor2 O2 sensor. Truck ran poorly until that was fixed. Pulled it out and it was just blacker than night, replaced it and all was good.

 

[Rocket Man]

It could be the sensor or the cat. To check the sensor you can swap it to the other side. Bank 1 is the driver side. This would be downstream sensors, the ones after the cats. Swap those sensors side-to-side and see if the code follows the sensor and now shows a DTC for bank 2. If so, it’s a bad sensor. If it still shows a code for bank 1, it’s the cat.

 

[PNWYukon]

What are the Possible Causes of the P0420 Code?
A faulty catalytic converter is the most frequent cause of a P0420 trouble code. Common issues that can cause this OBD-II code include:

• A failed catalytic converter
• A faulty oxygen sensor
• Circuit problems, such as damaged wiring and loose connections
• An exhaust leak

The odds of CAT being bad are pretty slim, but without diagnostic testing it is hard to say.

HO2S Bank 1 Sensor 1: This parameter displays the voltage from the signal produced by the heated oxygen sensor used to monitor fuel trim for cylinder bank 1. The scan tool will display a low voltage reading when that cylinder bank is running lean. The scan tool will display a high voltage reading when that cylinder bank is running rich.

HO2S Bank 1 Sensor 2: This parameter displays the voltage from the signal produced by the heated oxygen sensor used to monitor catalyst efficiency for cylinder bank 1. The scan tool will display a low voltage reading when that cylinder bank is running lean. The scan tool will display a high voltage reading when that cylinder bank is running rich.

 

[malmed]

To check the sensor you can swap it to the other side. Bank 1 is the driver side. This would be downstream sensors, the ones after the cats. Swap those sensors side-to-side and see if the code follows the sensor and now shows a DTC for bank 2. If so, it’s a bad sensor. If it still shows a code for bank 1, it’s the cat.

Thanks, brilliant idea, that will save me from buying unneeded stuff... I keep getting and clearing p0420 code, thats all I get is that code... so your idea oughta work!

 

[swathdiver]

Thanks, brilliant idea, that will save me from buying unneeded stuff... I keep getting and clearing p0420 code, thats all I get is that code... so your idea oughta work!

Trust your computer. If your O2 sensors were bad, the computer would throw O2 sensor codes. Your Bank 1 catalyst is bad. A fouled plug or leaking injector can kill a cat, not to mention a blown or leaky head gasket.

Cheap Chicom cats last less than a year generally speaking. Been down this road before and went Magnaflow through GotExhaust on here. @GotExhaust.com

 

[Rocket Man]

Any update? Did you swap the sensor to the other side? Curious if it’s the cat or sensor.

 

[malmed]

Any update? Did you swap the sensor to the other side? Curious if it’s the cat or sensor.

Not yet... I will do it this weekend...

 

[malmed]

Well, I took a chance and cleaned the MAF and new air filter... and so far (80 miles) no codes... I was getting them every 30 miles or so, maybe that did it? I'll update in a few more miles.... A friend suggested it might be that and/or loose conncections at the MAF, so I tighened and cleaned everything.... so far so good, I'll see... $350 to replace CAT.