P0140, 0172; 03 Trailblazer

SlothM0311

Original poster
Member
Sep 16, 2017
2
Corning,NY
A while back I had a misfire as the coil pack stopped working. I had to drive it home on a trip and imagine it mixed my oil with the unused fuel. I have finally had the time to fix the vehicle and take some time to look it over. I have changed the oil and filter when I got the P0172 "System too Rich Bank 1". I continued to receive this code and changed the upstream O2 sensor; I got an AC Delco that is required and put it in. Now, I am receiving the same P0172 but also a P0142 "O2 Sensor Circuit No Activity Detected Bank 1 Sensor 2". I'm wondering if this is saying the downstream needs to be changed now? If it helps, these are under Pending and not Stored yet. I did purchase the downstream AC Delco O2 sensor when I got the upstream. I was just lazy and a tad hungover from the mother in-laws birthday when I changed the upstream. Any advice would be greatly appreciated.
 

Mounce

Member
Mar 29, 2014
13,667
Tuscaloosa, AL
How long did you run it with the misfire? Run strong now?

Just wondering if you might have melted the cat with the unburnt fuel and the second sensor isn't seeing expected data so computer deemed it defective. But I would also expect a p0420 for "catalyst efficiency below threshold" if the cat was cooked.

Wouldn't hurt to eyeball the #2 o2 harness as well for damage causing a disconnect.
 

SlothM0311

Original poster
Member
Sep 16, 2017
2
Corning,NY
It was maybe 30mi. It runs like a champ, good acceleration and everything now. It just spits out those 2 codes. I am changing out the downstream sensor tomorrow.
 

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