Early shifting into OD. Strange readings on TunerPro RT

[yevgenievich]

This is the wiring diagram for the 4WD system. The dark blue wire on the right side of the page is going to the PCM. This would be where the 4 low signal would be sent, correct?

Any idea what the voltage should be if I'm in 2HI?

(BTW, I have noticed that the lights on the transfer case shifter (floor display) are constantly on. I am not in 4WD though.

Looks like circuit 1493 is the one that goes to PCM. Circuit 50 goes to the fuse box. Transfer case switch sends 12v to the ecm when switched.
Edit: looks like you found the full description which is consistent with the symptoms.

 

[FourEightZero]

Looks like circuit 1493 is the one that goes to PCM. Circuit 50 goes to the fuse box. Transfer case switch sends 12v to the ecm when switched.
Edit: looks like you found the full description which is consistant with the symptoms.

Not gonna lie... This truck is frustrating the hell outta me.

 

[yevgenievich]

Not gonna lie... This truck is frustrating the hell outta me.

From the description, it looks like ecu does not discriminate well when signal is floating. So that circuit should be verified for good gnd when in one position and good 12v when in other position.

 

[FourEightZero]

Backprobed the computer and that dark blue wire was showing zero voltage with the ignition on.

Pulled the connecter on the transfer case switch and saw plenty of exposed wire. Clipped it back to what's left of the conduit and connected the brown wire to the dark blue.

Saw voltage at the computer. Took the truck for a spin with TunerPro hooked up.

Vehicle speed matched the speedo. Tranny shifted normally. Gonna splice in new connector tomorrow and see if switch is still good.

Found the PDF of the tech bulletin if any of you need it.

 

[Schurkey]

Very good. Well-done.