As of a few days ago, the A3 c-code I was getting reset itself.

Also in the past few days, I have cleared the codes because the CEL keeps coming on. Sometimes it will go back off and others it stays on. Each time readings are slightly different.

Cleared codes - then when CEL comes back on I got:

P0300 Engine Random Misfire Detected

Cleared codes again - then when CEL comes back on I got:

P0300 Engine Random Misfire Detected
P0151 Oxygen O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)

Cleared codes again - then when CEL comes back on I got:

P0522 Engine Oil Pressure Sensor/Switch Circuit Low Voltage
P0151 Oxygen O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)

Cleared codes again - then when CEL comes back on I got:

P0151 Oxygen O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)

Cleared codes again - then when CEL comes back on I got:

P0300 Engine Random Misfire Detected
P0151 Oxygen O2 Sensor Circuit Low Voltage (Bank 2, Sensor 1)

Strange thing is, the truck is running great and when I check the I/M on the scanner it states that the "OS is OK", yet I seem to keep getting on the same scan the P0151 code. I did have a couple mechanics check this a few times when my CEL would come on when it rained and go off the next sunny day and they told me not to worry about it. But the sensor might be getting worse now.

If the P0151 code can also trigger a P0300 code, then the OS B2 S1 might be the culprit.

Suggestions before I start spending money and time?

 

How old is the sensor? (bank 2, sensor 1, that'll be the front O2 sensor on the passenger side.) That may be the root of some of your codes.

Not sure about the low voltage on the OPS though.... Bad connection? It isn't by any chance fed on the same circuit is that O2 sensor is it?

 

I would bust out the wiring diagram for your truck and find the oil pressure switch and the 02 sensor in question, then trace out the grounds for those two items. Do they travel through the same harness at some point? Share the same ground?

Since rain has such a heavy influence over what's going on, I would assume there's a grounding issue or corrosion in a connector. This will be a PITA to fix, but at some point you will likely unplug a connector and find a bunch of green corrosion that needs to be scraped out, or you'll find a ground connection that's nearly broken, badly corroded, or loose.

As you work through the harness plugs, I would add a little insulating grease before you plug them back in just to keep the water out.

I suspect that when you resolve the issue causing the 02/oil pressure codes, the misfire code will also go away.

 

In doing this I am using a new OBDII scanner that only cost $35.00 but had good reviews.

The O2 sensors (4) on the truck are all original and never been replaced, so I'm not surprised that they would be on their way out with close to 275k miles on the 2004 truck. YIKES ... The connectors and wiring under the truck may very well be damaged/corroded.

 

Yup, I can agree this will be one of those PITA jobs and I only wish I had a decent place to do the work. In 6 weeks the truck needs to get inspected and that's my rush. I need to pinpoint the problem and get it fixed.

Shared grounds may be an issue, but what I find mostly strange is, with all these various codes, the truck runs great and no dash gauges show any coinciding warnings or problems other than the CEL playing games with me. Since I did have an A3 c-code that eventually reset itself, I'm wondering if the FCM or fuse box may be triggering of some of these codes.

 

I don't think either of the sensors runs thru the fuse box though, except maybe the heater circuit for the O2...... for the sensor side, they are fed by the PCM, and signal returns right back to it.

 

Oh yeah, they don't last forever! You can use a scope or a much better scan tool to look more closely at the 02 sensor data, or you can just gamble and put new ones in.