Had the oil changed and truck left me stranded an hour later. Had the truck towed home, starter wouldn't turn, and relay 203 was buzzing, found fuse 34 blown. Replaced it and as soon as I turned the ignition to accessory position, fuse blew again and relay started buzzing again. Removed relay while key still on and put it back in and did not buzz, left blown fuse, turned key and starter turned but no start, then relay buzzed again. Fuse 34 says, PCM, fuel injectors, idle air control and mass air flow sensor. I unplugged all of those and fuse still blew. I unplugged the PCM and fuse did not blow. Left key on and reconnected PCM leads one at a time. Fuse blew after the lead to the left was plugged in. What could they have possibly done? They obviously were under the hood and under the truck to change the filter and remove the oil plug.

 

Probably pure coincidence. If they accidently damaged something, I doubt you would have been able to get one hour of use out of your vehicle before the fuse blew. You could do some visual examination of the underhood wiring harnesses for any obvious damage causing a short to ground.

You could have a damaged PCM with an internal short to ground from what you have described so far.If you are to go further, you really need a manual having a schematic of the wiring in and out of the PCM.