I have a 2000 5.9 magnum 1500 with 150k miles on it. It was my first vehicle and drove it everyday until it started acting up and I couldn’t fix it so I’ve come here for help.The truck won’t start now unless the OBD2 reader is plugged in and even then it runs rough,and if you unplug the scan tool the truck will die and won’t start back up.

 

Does your scan tool show any codes? Or pending codes?

 

The scan tool doesn’t show a code

 

Verify you are getting spark, and fuel pressure.

 

Start with the basics, power and more likely grounds. The data link connector has two pins (4 & 5) that connect to different grounds in the vehicle. The ground on pin 5 is the same that the PCM uses, might be the scan tool connects the two pins internally and provides a temporary (and crappy) ground. Pin 5 goes to G105 on the front of the engine, black/tan wire. .