So I have an OBDII code P0138 O2 Sensor Circuit High Voltage.
Our 5.9 only has 2 O2 sensors and both are B1's (S1 & S2) Pre cat and post cat.
Both are OEM NTK Branded, so they are overdue for replacement anyway
There are other misc ODBII codes to indicate the O2 status, as in ...... being sluggish or slow to respond, the heater in it has failed or malfunction detected, ect.
In light of How many codes I could get, I am not even sure the O2 is my badguy to begin with.

I need to figure this out quickly because the state inspection renewal is due soon.
So to get things up to speed after the AT issues were cleared and the truck was cleared for going back to being a fulltime DD, I did some much needed exhaust work.

The OE twin tailpipes were long gone before we got the thing so the shell of what used to be a muffler was echoing off of the undercarriage making it sound bigger,badder, and almost like dual straights with glass, and of course more importantly made the gas gauge drop faster than it should.
A 15-20 mile round trip should not consume just over 1/4 of a 26 gallon tank of fuel.

Factory MPG reads as the 5.9 Magnum 360 gets 11 City/17 Highway/13 combined ( @16 yo I do not expect to get OE est MPG)

After a refuel the tripOD was reset.... With the New muffler,bad flanges and small leaks, it reads that 50.4 miles has used the same 1/4 tank that a 15-20 mile one did.

So the OE Muffler LOOKED LIKE THIS ONE but not stainless and a bit rusty

I am not sure if the if the code is being thrown due to a leak in the exhaust line, or maybe up top in the vac lines, but I do know that the manifold flanges are shot, and in the splicing of the new muffler I have 2 small leaks.

If it is in fact an exhaust leak making the code appear (i doubt at this point), I dunno if the cat is intact/clogged/or banged out, but I am wondering

#1 with the shot flanges how the hell is S1 not throwing a code,
#2 why the hell would proper backpressure make it go buggy with bad flanges and 2 post cat/o2 leaks if incorrect backpressure with the same bad flanges but no post cat/o2 leaks and a lot less pipes did not

What would be the most likely issue I have (aside from a dead O2) of the code simply being a passed on side effect of something completely unrelated?

This is the replacement I put on instead since a "Y" into 1 into 2 system is for more for curb appeal at the bumper and not for any beneficial purposes at all.

IS this one

 

Clear the codes, and see how quickly they come back. If your O2's are original, it sure wouldn't hurt to replace them in any event...... Disconnect the battery while you do so, let the PCM learn the new sensors.

 

See, I know about clearing the PCM and all that jazz. I had a ghost code to clear from the CPS going out, and before that the was one for the shaft output sensor......So I cleared those together and left it alone for a week.

The tranny proved itself fit for full service--No codes for ANYTHING.
Then I removed what was left of the OE resonator pipe (cut the rusty U-bolt/slit the pipe and pulled it off ) to make room for the New muffler to fit.

The day after install is when it decided to go CEL on me, Which is why I automatically assumed the exhaust changes were just to much for it.

To totally clear the PCM of both it's CEL codes, and LEarned sensory responses How long should I leave the Batt disconnected?

I am into small/home electronics repair on a level enough I understand the whole residual charge crap, and that is why I ask.

I know with a desktop PC the safest fastest way to discharge the residual charge in the system is to try to turn it on after it has been disconnected from the wall outlet. Since it doesn't realise it it has been unplugged from the wall due to the residual, in an attempt to start booting it will instantly consume ALL remaining residual charge.

I could technically duplicate the same effect simply by turning on the headlights, or turning the key to the full to start.

 

How many miles on the truck? Cats don't last forever either. I put on a magnaflow cat some years ago. Just touch the battery terminals together, This will clear any memory out and you don't have to wait.

 

Speaking of...

That would be more of a mileage (engine hours) type of thing than age, right?

If I had a bad plenum and some oil/cr@p got into the cat but not enough to plug it, would it eventually burn itself off and out of the cat?

I had a bad plenum with unknown number of miles of it (before I got the truck) before I replaced it. I pulled the o2 sensor and it did not seem to make any difference. I am just new to these trucks and I am not clear what a "clean" cat and Dodge power should feel like. It has plenty of power, to me. Only 70k mikes on the truck. I just want to make sure it's not strangling the power.

 

I Disconnected, turned the key full over, and waited 20 minute to reconnect.
the Cel came back on in 10mi. I edited my sig to include mileage, and I was suspecting the cat more than the O2 to begin with......I am planning on getting an OE direct fit with the crossover pipe and lower flange collars all included.
I will get one of the Laminate flange kits I mentioned before, split it and pick up a pair of G8 bolts-n-hardware.
(one kit does one side and usually 4 laminated flange halves, 2 bolts, 4 washers, 2 lock washers, 2 nuts)

 

Just an update, after clearing the CEL, and having the it come back on.... I decided to pop a fuc*itol, and ignore it until I am able to get the cat ordered and put on to procede.

Well We were out making rounds and running errands and it went off ON IT'S OWN!??!?

It seemed too good to be true, and apparently was because after being home for a few hours another run was needed......it came back on.

 

So for the most part the Cel idiot light stays out....

It generally only comes back on if the truck has been ran to operating temp for a while, shut down and run again.
Pretty much the typical trip of going to the store, shopping and going home.
It usually comes on within 5-10 minutes.

At this point even though the O2's are OEM NTK-Heated, and the Cat is Also OEM, meaning both are 15/16 years old.....I am not truly convinced that they are the issue right now.

If there is anyone that has dealt with and solved the same issue and would be so kind to pipe up with what they did, would be greatly appreciated.

 

Sensors don't last forever.

 

No need for all the guessing games. Pull the O2 plugs and check resistance across the white wires, it is supposed to be 4-7 ohms. If you get infinity (which 99.9% you will) then the sensor is shot and you replace it. This is per the FSM