I was sitting in my truck, minding my own business, when the check engine light came on. P1389 "No Auto shutdown voltage". I have no idea what that means. The truck continued to run fine, over the next week or so, I used it for several hours, and it ran fine. I checked the alternator, and it was fine. I checked the ASD relay, and it was fine. The wires going to the computer seemed to be sending the right voltage. Everyone I talked to said it had to be a bad PCM. Ok, I bought a PCM and plugged it in, and the error was gone. I drove a few miles and the error came back. I drove a few more miles, and the computer literally blew up. So, now I'm a little frightened to put another computer in it.

Has anyone experienced this? any idea what could cause the error when it all tests ok? what could have caused the computer to explode? None of the mechanics I have talked to have ever experienced a computer exploding or had to work on a car where that happened; They all assured me there's no way it could happen from a wire short or bad (external to the computer) component, that it had to be something in the computer. That could explain the blowing up, but not the repeated P1389.

 

Not a computer problem.... ASD relay supplies power to the coil, injectors, and a few other twelve volt tidbits, so, if it wasn't working, the engine wouldn't be running. The PCM gets a 12 volt feed from the ASD relay, would have to consult wiring diagrams to see just which wire it is.

You can download the factory service manual for your truck from here. Wiring diagrams are in section 8W.