3406E jakes will not engage

codes 31 and 36 are loss of wheel based vehicle speed and invalid wheel based vehicle speed signal respectively and 34 is primary engine speed loss of signal. Perhaps the ECM thinks the truck is not moving so it won't engage the Jakes???.

 

If the solinoid is energizing and the soiniod clicks the ECM is activating the Jake's, it is an oil, or assembly problem

 

By pushing down on the center of the solenoid you should be able to activate jake brake for two corresponding cylinders.. If you push and nothing happens the problem is mechanical not electrical

 

Check the rocker shafts, are they installed with the flat side up? Seen them installed upside down causing lack of oil supply to jake due to massive leak.......