Chasing Code issues 2015 Tahoe (P0430 and Tighten Gas Cap)

[bonedog]

Update: replaced both O2 sensors on the passenger side. After driving for a bit, two codes were thrown: P014A and P0158. Just to test what's happening, I cleared the codes and the only one that's shown back up is P0158. That seems odd that a new electrical code would show with the OEM O2 sensor installed. Any suggestions?
As of now, my thoughts are to go back under and check the wiring/plug and make sure I got it on tight. Or remove the new sensor and put the old one back in. Note that the "old" sensor was only 6 months old...

 

[Doubeleive]

Update: replaced both O2 sensors on the passenger side. After driving for a bit, two codes were thrown: P014A and P0158. Just to test what's happening, I cleared the codes and the only one that's shown back up is P0158. That seems odd that a new electrical code would show with the OEM O2 sensor installed. Any suggestions?
As of now, my thoughts are to go back under and check the wiring/plug and make sure I got it on tight. Or remove the new sensor and put the old one back in. Note that the "old" sensor was only 6 months old...

swap the questionable 02 sensor to the other side and see if the code follows the sensor or remains in the same location
keep it simple
as for "tighten gas cap" technically that is a "small evap leak" regardless if it throws a code or not. if you replaced the gas cap with a oem cap and the message remains then you have some other evap leak, either one of the solenoids (usually the front one for a small leak) and/or rear one & the canister. if it is a issue it's usually cheaper, easier and faster to just shotgun it and replace all 3 and call it day.
I was under the impression the 15+ had no gas cap, my 18 does not.

 

[bonedog]

So...came home and took out the "new" O2 sensor from Rock Auto and put the old one back in. Codes are gone so i'm having Rock Auto refund the part.
Now.....I'm back to checking to see if the original Catalytic code comes back on. Here's hoping it was just the upstream O2 sensor...

 

[bonedog]

And I spoke too soon. P0158 code came back up repeatedly. I can’t tell any pins being bad in the harness connector but I can tell you it was a bear to originally separate the connector.
Anyone know what it takes to possibly replace the connector from the harness (not from the sensor)?

 

[Fless]

Swap the sensors side to side to see if the code follows.

 

[bonedog]

It does not follow. Isolated to the one downstream bank on passenger side. Two sensors tried and both are good on driver side and both bad on passenger side.

 

[Doubeleive]

It does not follow. Isolated to the one downstream bank on passenger side. Two sensors tried and both are good on driver side and both bad on passenger side.

then next up is a ohm test on the wiring harness, I am not sure what the specs should be but if you suspect the connector check one pin and then go up the wire harness a bit and probe the wire from the wire to the pin it should read zero on each side that will tell you if it's in the connector or not or if it's up higher somewhere, if nothing pans out there then check the harness ohm's and see if they match factory specs, maybe @swathdiver has that info.

 

[BlackandChrome]

I'm getting "Tighten gas cap" on some of my start ups on my 2015 Yukon. I haven't had a CEL or code.

Looks like I'll try and swap the gas cap and see if it fixes it.

 

[THarber]

I want to remember that the tighten gas cap message only reads when the tank is at 1/4 full. Also replace it with a GM cap, not china.

I think the OP is in early stages of a bad cat. When the truck is started up initially, it will read high voltage but then as the cat warms up, voltage should drop. You should see readings 0f .45 to .50 volts. If the volts do not change at all, its a wiring issue. You might even have a bad MAP sensor, vacuum leak of bad MAF.

 

[Fless]

I want to remember that the tighten gas cap message only reads when the tank is at 1/4 full. Also replace it with a GM cap, not china.

I think the OP is in early stages of a bad cat. When the truck is started up initially, it will read high voltage but then as the cat warms up, voltage should drop. You should see readings 0f .45 to .50 volts. If the volts do not change at all, its a wiring issue. You might even have a bad MAP sensor, vacuum leak of bad MAF.

Partially correct. The evap test is what triggers the leak code, and that test is done with the fuel tank level between 1/8 and 7/8 (some say 1/4 to 3/4, but you get the idea). There are other conditions like the ambient temp vs the coolant temp (must be within x°) so typically on a cold start.