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@Dionysus thanks for the pic. Since there are 4 codes that point to Bank 1 (O2 sensor, knock sensor, charge air sensor) there may be an issue with the wiring harness/plug leading from Bank 1 to the ECU. Perhaps a coolant leak got into the plug somewhere in the rear of the engine. @TravisBekk Can you Black Light that area in total darkness to see if there is any coolant leaks?
That's a solid theory you have. With an only one-time visit to this valley on the V6, I wasn't very impressed with the harness to the knock sensors; not the best quality. The main harness junction behind the engine was bulky and overly difficult to maneuver...like wrestling with an alligator. Harnesses usually fail at connectors or pinched wires, both of which can be intermittent (most of the time it works; once in a while it fails, then back to working). I say this too, BC my experience with knock sensors, they rarely fail.
Back to your theory, if all of the banks sensors are fed with a common +v and it is pinched somewhere...I can see that. Same with a common ground.
BTW, I can see, in a couple of places, if there is coolant sitting in the valley on a V6 fully assembled. A bore scope can get there too, but I didn't really have to use it. No connectors other than the two at the knock sensors would/could end up under coolant water. The two harness connectors to the knock sensors definitely could get under water. You can see from my pic the harnesses lay at the very bottom of the valley. In fact, there are cable clamps using the screws of the oil cooler to hold them down there.
One clue is the P0054-00 bank1 (right side) sensor 2 (in the cat) or the cat itself may be failing:
You could swap the bank 1 sensor with bank 2 and see if the code changes. Then just replace the bad O2 sensor and see if the other codes disappear. If not then check the wiring to the knock sensor and charge cooler sensor to see if there are any disconnects.
If it was an injector you would likely smell gas or get some weird smoke from the exhaust with a specific misfire code.
Recording real-time fuel trims using your OBD2 scanner is helpful too.
Good luck - Can you report back on your findings?
Just to follow up. I ordered some spark plugs and an O2 sensor from Rockauto, they should arrive in about 2 weeks and I will change those out. Today I did an intake clean using some CRC cleaner because I was able to find that locally. I used some instructions that were posted here for the BG method inserting it into the large vacuum port just behimd the throttle body (possibly PCV port?). I ran about a can and a half through but I was getting nervous because it was getting hot and I didnt like the sounds it was making. I let it soak for about 15 minutes and then took it for a drive, slowly working my way up to running it pretty hard. Once I started really getting on it, it was dumping quite a bit of carbon and black smoke out the exhaust, but eventually cleared up after about 2 minutes. It drove great after a few minutes but seemed to have had slightly less "break the tires loose" power. That could be due to the wet roads and my nerves. When I pulled into the driveway, the engine seems to be running smoother but there is still something slightly not right. I pulled the codes again after that drive and I am still getting the charge air temp code but nothing else. I am still trying to figure out if there are 2 charge air sensors or only one. I see the one on the left side that is a Volvo part, but I can't determine if there is one for bank 1.
@TravisBekk It would be helpful to know which codes were active and historical (permanent) when your CEL went on. Some OBD2 readers will give actual dates for each code. The Venn Diagram for your 4 codes is a tough putt to figure out.
Also recommend collecting some real-time fuel trim data while you are doing your OBD2 scan. If the engine is rough this may be a way to diagnose any subtle fuel/air mismatches that are not yet producing a CEL.
With your aviation background it would be interesting to see the results and your interpretation.
