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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?

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...

The A0 has no data bus to tap into for information… the only two electronic boxes onboard are the TCU and the CTIS and they are not wired together. Only a maintenance connector for the trans controller…

Baro and not boost, is it pre-turbo?

Is k26 energizing With ign on? Thats the neutral start relay controlled by the trans. K26 powers K11, K11 when energized sends power to the start switches to allow engine crank using those switches as they feed the aux start relay on the frame… trans trouble may indicate something in the...

You only get air out the rear when you turn on the trailer air control AND the park air control in the dash...

right front might be a sticking wheel valve refusing to seal. the right line goes from the dump valve thru the hub to the banjo fitting on the wheel stud. then thru a hose to the wheel valve. unscrew the banjo bolt on that wheel and confirm that it is indeed a banjo bolt and not a solid...

Disconnect the line at the PCU i mentioned earlier that feeds down to the dump valves and wheel valves, and using a blowgun on that line, give it a brief shot of 60 PSI air. That shot of air should open the wheel valves and all the tires should equalize at the same pressure. As long as you...

he said they are dumping to 10PSI... it must be mostly blocked, as the system must build enough pressure to open the wheel valves in the first place... so air is coming from some place(leaking wheel valve, leaking PCU supply solenoid). a system open to atmosphere would have trouble building...

Quick fix, on the back side of the pressure control unit under the passenger dash on the port labeled C I think, disconnect the line to the wheels. The other line is the pressure input from the wet tank. The pressure line typicallt has a T right where it comes thru the floor as that air also...

woops, missed the 1078 2000 model. cat 3126 should have an ex brake butterfly assembly connected to the turbocharger output...

What year and model truck are we talking about? On the LMTV, Not retarder, exhaust brake... The retarder is a hydraulic brake system built into Allison 3000/4000 series transmissions as an option. The MD3070 AWD trans we use is incapable of it as the transfer case occupies the space on the...

The tire lift cranes sometime get stuck in the up position, are you referring to that?

Wow, an actual bad relay! Cool, that doesn’t happen very often:)

in the drawing I attached that same 12v should also be on k10 pin 87 and is what feeds thru the relay to pin 30 when k10 energizes, to light the brake lights. it may be you have a bad connection somewhere along the source path from K6. it delivers measurable voltage unloaded and enough current...

K-30 and 31 are for feeding 24v commercial trailer lights via the 10 pin rear connector. You can remove them if you wish… pull K10 and connect a meter from pin 86 to 85(ground). You should see 12v there when you step on the pedal… You can bypass the light switch by jumping pin K to C which...

K6 is a good sign, means the switches are OK. from K6 it passes thru the light switch and activates K10. K10 switches the light output from flasher to brakes. Flashers working means K10’s de-energized contacts(30-87A) and all the rest of the light circuit is also OK. So I suspect you have...

What truck do you have? The brake circuit is different between the A0 and A1…

mine is already separated and that upper frame rail(now my floor assembly) is still light enough to be lifted… Have you sourced that part?

Could have been the PTO gears wearing in…