U300FIgnition Input Accessory
- Generic OBD-II code · Network
- How the car detects it
- U300F refers to the accessory input, the line that powers comfort loads such as audio or power windows when the key is in accessory. In GM's 2012 pickup wiring manual this accessory voltage circuit is active in accessory and run but switched off in crank and in both off positions. A module stores U300F when that pattern breaks: voltage on the accessory input with the key out, or none while the body controller broadcasts accessory or run. No manufacturer documents U300F publicly. Since the accessory feed is often routed through a relay and shared by many consumers, a stuck relay can leave radio and windows working with the key removed and slowly flatten the battery, whereas an open feed simply kills those functions; checking which of the two applies is the first step.
- What you may notice
- Radio, windows or sockets dead in accessory, or still on with the key out
- Battery drained after parking when the feed stays live
- Likely causes
- PossibleAccessory relay sticking closed or not pulling in
- PossibleBlown accessory fuse or open feed wire
- PossibleWorn accessory contact in the ignition switch
- RareAftermarket equipment backfeeding the accessory line
- Repair
- Easy · Often possible to do yourself.Typical cost: €10 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.