Repeating O2 sensor codes :(

View of the carnage, or all CEL codes for the past four years related to the header nuts coming loose and causing an exhaust leak. Entirely solved by installing new factory exhaust manifold studs, nuts and securing with home depot lock washers.

While diagnosing the issue I easily replaced both upstream o2 sensors six times per side. In addition, for at least 24 months I would remove the o2 sensors and soak in gasoline overnight to "clean."

I believe the stud nuts coming loose is the issue because when I put on lock washers the CEL goes away. Even on a different engine, when there are no lock washers the same CEL comes back on.

 

I'm sure you've checked this already, but did you replace your gas cap yet? (or using a non-manufacturer one)
Just an easy check/replacement to try.

 

Yessir, replaced the gas cap at least three times. Issue did not arise until I installed the JBA long tube headers. The remainder of my troubleshooting should be listed in previous postings.

I thought I had the issue resolved when I discovered the ecu relay was shot using the fog light test.

However until I began gagging on exhaust fumes in the cab I did not think to look for exhaust leaks. I found the leaks by getting under the truck and looking for holes.

I am, right now, reading a variety of hotrod forums about their using lock washers on their header studs ...

 

Update to my earlier replies, dealer kinda gave a hook up with 4 free sensors, and an exhaust gasket. Problem was only fixed once I told them the problem occurred after I dropped the transmission and replaced the clutch. The issue was some messed up wiring around the transmission area... bottom line I lucked out with a $500 price tag.

 

Did you ever find out what that "messed up" wiring was? Just had my transmission out and now I'm having the same problem.

 

Never did find out exactly, but after being in the industry for so long there is alot of agreement that certain lights come on with certain codes and they can only be shut off by a dealer and along with that usually the code is never related to the actual problem. Mostly a money grab thing for the dealer to try and sell you something for a quick buck. If you know what your talking about and the service manager realizes this than you might luck out with a lower price tag. Again this is a theory if you will but lots of techs and retired mechs agree on this for certain dealers.

 

Maybe you switched o2 sensor harnesses..

 

Good point. However, I have the URD harness's and I checked those.
I addressed following additional points of failure in my quest to get rid of that CEL. Each had moderate to good results in mitigating:
1. All the connections in my URD purchased, Doug Thorley exhaust, and headers needed attention on multiple occasions.
2. URD's gaskets, 10.9 grade bolts and nuts, and Nordlock lock washers fixed the leaks in my Doug Thorley Y pipe connections.
3. Although I did have to adapt the exhaust hangers so that they did not put undue flex on the joints.
4. The rear O ring leaks and the most recent fix included:
A. 10.9 grade bolts and nuts from either tractor supply and/or autozone;
B. Nordlock lock washers;
C. I am planning to try the newer permatex right stuff gasket maker should it leak again.
D. In addition, the bolt holes in my URD performance exhaust are beginning to break out. So I can see having a stronger flange welded on at some point.
5. Replaced the brake booster. Although simply replacing the front gasket would likely have accomplished the same.
6. Repaired mulitple leaks in the vacuum lines.
7. Doubled up the JBA-063-2035 Toyota 4.0L Header Gaskets gaskets on my URD headers.
A. Meaning, I put two Header Gaskets on each Header.
B. Even with having had the Headers planed down by my local hot rod shop, they still sit at such an angle they required a second gasket in order to seal.
C. I doubled up the header gaskets because I am not proficient enough in using RTV to realistically have sealed my headers that way.
D. I swapped out the header bolts with stainless ARP studs, ARP nuts, and tightened with Nordlock lock washers.
8. Regularly cleaned the MAF sensor.
9. Sealed the Maf sensor port in my URD TACI.
10. Replaced the gaskets in my valve covers and intake phylum.
11. Sealed the previously sealed areas in the valve covers with additional FIPG.
Before my engine catastrophically failed this spring, I want to say the CEL had come back? Usually, it comes back when one or more of the joints in the exhaust and headers has loosened enough to begin leaking. When completing any and all of the above fixes, it seemed the CEL would stay banished for a week or three, but then invariably return.

 

Definitely was not the O2 sensors as those rarely fail. I spent over $1,500 replacing those before I decided I was throwing money away on that as a fix.

 

In my whole career I have only replaced about 2 o2 sensors. One, was physically damage and one had a bad wire, so close to the sensor that I couldn’t solder. Before changing anything, do proper diagnostics, the purpose of the sensors is to trigger a code if the A/F ratio is not within parameters. this could be to a lean or a rich mix. Sometimes something as simple as a vacuum leak pass the MAF could trigger a snowball effect. All components have testing means for you to test resistance, continuity, etc. In conclusion, act as a technician, not a part changer. Cheers!