So on my 08 6.7, I have 2 aluminum lines that used to hook to my dpf system. They go from the system to a sensor @ the top of the tranny. Was wondering what these are for? My 4wheel drive flashes on 4 low when I try to use it and 4wheel high makes the truck feel like it is sinking even on dry land. Help please! Thanks

 

The sensor on the transmission is a differential pressure sensor for the DPF to tell the ECM when the DPF is full and needs to be regenend. If you are using a SMARTY programmer the Differential pressure sensor is left open to atmosphere per the SAMRTY instructions. My Al tubes and hoses are tied wrap to the DPF and stored with the DPF still connected to the sensors in the DPF.

As far as your four wheel drive problem there may be another sensor or controller that has failed. I would also check to see if the electrical wiring is still intact and connected.

Jim W.

 

Thanks jim. I wonder which sensor it is, I was on the beach in south texas and it felt like when I switched it to 4wheel drive just to be sure. It felt like it was sinking. Turned off 4wheel drive and it felt fine.

 

That is strange. I have had both of those lines plugged off for 2.5 years and no troubles. Running Smarty JR on the fuel economy setting.

 

I'd think that either open to the atmoshphere or plugged that the pressure would be the same inside the sensor and it would see no differential... Hence, no issues plugged or left open...

 

Did you lower the air pressure in the tires when you tried 4 wheel drive? On sand when the truck is in four wheel drive the truck will be more aggressive and dig into the sand easier. By lowering the air pressure in your tires this will spread out the mass of the truck over a larger foot print. Similar to a track type tractor with larger tracks on the tractor this provides a lower ground pressure for floatation of the tractor.
This is also an old 4-wheeler trick from my days when running on the Michigan sand dunes in Silver Lake Michigan.
Jim W.

 

I just followed the Smarty instructions that said to leave the differential pressure switch open to the atmosphere. I have been this way since March of 09. I think the reason Mad’s suggest to do this is to prevent a leak from a closed line affecting the switch, if both stay air tight then you should not have an issue.
Jim W.

 

I think the lines I'm referring too Is the vaccuum lines that go in with the dpf which I guess have nothing to do with the transfer case. But why would my 4wheel low flash on the turn *** switch and never go to 4wheel low?

 

Did you come to a complete stop before trying to put the truck into 4-wheel low? I believe that in order for the transfer case to go into 4-wheel low you must come to a complete stop then engage the 4-wheel low feature. When shifting out of 4-wheel low you again need to come to a complete stop, shift out than continue on.
I am going from memory so do not crucify me if I am wrong in operation of the 4-wheel low feature, operating manual is in the truck.
Jim W.

 

Yes sir,came to a complete stop. Even put it in park and tryed it. Tryed it in N. It still just flashes.

 

well, maybe the selector motor or mechanism is internally failed.