LMTV 3126B Barometric pressure sensor fault code and location

[Keith Knight]

I’m getting a fault code 108 3 Barometric pressure. Voltage above normal or shorted to high source.
I was planning on replacing the sensor but cannot verify the location of this sensor any know where it is? I believe the boost pressure sensor is the same part and I don’t want to replace the wrong sensor.

 

[Keith Knight]

I unplugged what I believed to be the barometric pressure sensor and the I got another trouble code that was boost related and had the same description “ voltage above normal or shorted to high”
So it definitely sounds like a bad or disconnected barometric pressure sensor. But where the heck is it?
Actually it can’t be disconnected because I’m getting a barometric pressure reading of 29 which is correct for Florida.
This is the boost pressure sensor.

 

[Ronmar]

Baro and not boost, is it pre-turbo?

 

[simp5782]

.

 

[Keith Knight]

I’m looking for barometric pressure sensor.

 

[Keith Knight]

Cat 3126b is turbo. I found the boost sensor but still can’t find the barometric pressure sensor.

 

[Keith Knight]

Baro and not boost, is it pre-turbo?

Not sure what you’re saying.

 

[Ronmar]

Not sure what you’re saying.

Well anything in the manifold after the turbo would be altered/boosted. If this is sensing barometric pressure as a reference, it could be just about anywhere

This diagram says it is forward and inboard of the boost sensor… looking at the diagrams it says that sensor is optional/only used for certain ratings…

 

[Keith Knight]

Great picture! I just found a different picture showing it in the technical manual. Focus on item numbers 15 & 19.
19 I’m assuming manifold absolute pressure or commonly called MAP sensor which could also be call barometric pressure sensor.
Problem I’m coming across is I don’t have item number 15 but I’m getting barometric and boost data on my Bluefire. I’m only getting the barometric trouble code under normal operating conditions. I unplugged item 19 and the I got a boost trouble code plug it back in and boost trouble code goes away. Can that sensor show boost and barometric pressure?
It’s not making sense!!!!!

 

[Keith Knight]

Also the part numbers are only one number different.
And why does it say resistor thermal, atmospheric sensor and not barometric?

 

[hike]

Great picture! I just found a different picture showing it in the technical manual. View attachment 931555View attachment 931557View attachment 931556Focus on item numbers 15 & 19.
19 I’m assuming manifold absolute pressure or commonly called MAP sensor which could also be call barometric pressure sensor.
Problem I’m coming across is I don’t have item number 15 but I’m getting barometric and boost data on my Bluefire. I’m only getting the barometric trouble code under normal operating conditions. I unplugged item 19 and the I got a boost trouble code plug it back in and boost trouble code goes away. Can that sensor show boost and barometric pressure?
It’s not making sense!!!!!

As I recall, if you don't have 15, ECM has a default static barometric pressure.

If you recently reprogrammed ECM it is looking for sensor and not finding it, (error code), though still using statice default pressure—

Also the part numbers are only one number different.
And why does it say resistor thermal, atmospheric sensor and not barometric?

I believe the CAT part numbers are one number different—

 

[Keith Knight]

That would explain a lot. But this trouble code did not show up years ago after I replaced the ECM with a new one from cat. There is an empty plug in the harness that is in the location of where that sensor should be.

 

[Ronmar]

Wonder if it is supposed to have some sort of plug/cap that perhaps holds the electrical circuit in a particular state, like the data bus end resistors? Or perhaps something shorted it?

 

[Keith Knight]

What do yall see on your trucks? Do you have this sensor? Do you have this trouble code? If you don’t have it then why?

 

[hike]

What do yall see on your trucks? Do you have this sensor? Do you have this trouble code? If you don’t have it then why?

Our 3126b originally configured at 275hp does not have the barometric pressure sensor. My casual studies suggest a 330hp 3126b does. The code in our unit showed after flashing the ECM for 330hp. The pressure reading is unchanging.

Perhaps we had the code before, though I am pretty sure not. We had codes related to voltage we worked through and resolved before reflashing. I beleive when we add our missing sensor the code will go away—

 

[GeneralDisorder]

The 275 HP 3126b does not have the barometric sensor. The 330 HP flash wants it but doesn't complain with a check engine light. The fault codes is only there if you scan the codes.

Barometric Sensor part number for the 3126b is 194-6722

You need to replace the boost pressure transducer also. They fail and limp mode for that one REALLY sucks. It's about 10-20 mph tops.

 

[Keith Knight]

After my original ECM died and I purchased a new one from cat and they flashed it to 330 hp I never had it connected to something that could read codes until the other day at cat when they changed my speedometer pulses for the eco hubs.

Thanks guys, So that mystery solved!

Now for a solution. If I put 194-6722 atmospheric pressure sensor on, would the trouble code go away? Would it be recognized by the ECM? Would the ECM like it or confuse it because of the static barometric pressure is programmed in there?
The biggest question is would the engine benefit at all by doing this?

 

[Keith Knight]

oops

 

[Keith Knight]

Looking at both of these sensors pricing, typically I’m all about original Cat parts but they are each $260 from cat and after market are around $50.
Anyone can add there 2 cents about which is better the same etc.

 

[GeneralDisorder]

I had one customer that bought an Amazon one and his truck wouldn't even drive after installing it. Had to get one from CAT. Beware anything aftermarket.

I have not noticed any difference in performance. But it's there for a reason I assume.

Installing the sensor will clear the code. You don't have to do anything.