There has to be 12 volts to the Engine Computer, otherwise the engine wouldn't run at all. That is not a fuse issue. There are always at least three 12-volt power supplies to the computer, and on Chrysler products, usually four. One is live all the time to maintain fuel trim data, learned sensor personalities, and any diagnostic fault codes. A second one comes from the ignition switch to turn the computer on. The computer turns on the automatic shutdown, (ASD) relay for one second when the ignition switch is turned on, then again during engine rotation, (cranking or running). That relay sends 12 volts to the injectors, ignition coil(s), fuel pump or pump relay, and a number of other places, including right back to the computer to verify it got turned on, and it can be where the voltage regulator monitors system voltage. If any of those 12 volts is missing, the engine won't run.
If your code reader worked on this truck in the past, then it speaks the correct digital language, and you may be correct that the fuse to the datal link connector is blown, however, that fuse feeds a number of other circuits, so you should have additional symptoms or dead circuits. Let me know if that is the case.
With your code reader not working, Chrysler made reading fault codes yourself much easier than any other manufacturer. Cycle the ignition switch from "off" to "run" three times within five seconds, without cranking the engine. Leave it in "run", then watch the code numbers appear in the odometer display. The shaking you mentioned is most like a misfire. On the '96 and newer models, misfires are monitored and counted, then a fault code sets to indicate which cylinder(s) are responsible. Those are fault codes P0301 through P0308, and since misfires increase emissions, those codes turn on the Check Engine light.
Once you know the fault code numbers, you can go here:
https://www.2carpros.com/trouble_codes/obd2/p0300
to see the definitions, or I can interpret them for you. You also said the "engine runs up and down". Do I take that to mean the idle speed varies up and down? If so, that is related to intermittent misfires. Idle speed will also be too low if you disconnect the battery or the Engine Computer. So low, in fact, that the engine may not start unless you hold the accelerator pedal down 1/4". It will typically stall at stop signs too. If that happens, there is an extremely simple solution, so don't waste money on random parts in an attempt to fix that.
I'll be back tomorrow, typically early evening, to see how you're doing. Let me know if you need diagrams for the 12 volts feeding the diagnostic connector. I can usually find layout drawings for fuse boxes too if you need that to know which fuses to check.
Jan 24, 2026 at 7:51 PM
