I have a 2003 5.9L with an overdrive problem,wont shift into overdrive.Codes are P0123 (hi TPS) and P0753 (3-4 solenoid). Looks like the overdrive selonoid is staying energized and not allowing it to shift.When looking in the motor diagnostics section the APPS volts change from 0.3v at an idle to 3.5v at full throttle.When we looked in the transmission diagnostics section the APPS voltage is failed hi at 4.98v(not changing). We disconnected the TPS and the motor APPS went to 0v with the transmission side at 4.98v. The transmission shop inst sure where to go since we were betting it was the TPS. Anyone have any suggestions on what to try? are wiring diagrams available that show how this all works? Does the TPS have 2 seperate outputs,one for the motor and one for the transmission? any help would be greatly appreciated.

Thank you
John

 

If you disconnected the APPS and turned the truck on, the ECM has to be reset. This throws the calibration off and the ECM doesn't know where the pedal is.

When you reconnect the APPS, turn the key to run and SLOWLY go through the full range of pedal movement.

Also, if it's showing full throttle, that's telling the ECM to ground the 3-4 solenoid which causes the kickdown to 3rd.

The ECM looks for several factors for the kickdown. Throttle position, speed, engine and engine load.

If you are at a slow enough speed and the ECM sees more than 75% throttle, it's going to ground the OD circuit and kickdown to, or in this case maintain, 3rd gear.

Replace the APPS and you should be good.

 

Thank you for your help,parts are on order.