U300F code meaning
Ignition Input Accessory
What U300F means
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.
U300F at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyEasy, DIY possible
- Typical labor0.3 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U300F
- Radio, windows or sockets dead in accessory, or still on with the key out
- Battery drained after parking when the feed stays live
Common causes of U300F
- PossibleAccessory relay sticking closed or not pulling in
- PossibleBlown accessory fuse or open feed wire
- PossibleWorn accessory contact in the ignition switch
- Less likelyAftermarket equipment backfeeding the accessory line
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Ignition inputIgnition switchIgnition wiring
What each part of U300F means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 0F | The exact fault in that area. |
What to do next
- Note U300F and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U300F
What does U300F mean?
U300F means "Ignition Input Accessory". U300F refers to the accessory input, the line that powers comfort loads such as audio or power windows when the key is in accessory. It is a generic code, so it means the same on every make.
Is it safe to drive with U300F?
U300F does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U300F fail an emissions test?
U300F is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U300F to fix?
Difficulty: easy. A typical repair takes 0.3 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will U300F clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.