U300EIgnition Input On
- Generic OBD-II code · Network
- How the car detects it
- U300E deals with an ignition input that should be live only in On, without Start. Such run-only feeds exist because many loads are shed while the starter turns; GM's 2012 truck wiring manual, for instance, keeps its retained accessory power relay energized in all modes but two, crank and off-awake. If a module sees this run-only line high in Off or Accessory, or low while the network reports run, it stores U300E. A brief drop during cranking is intended and must not be judged as a fault, so a module that flags the code right after every start points more to a timing or software issue than to wiring. No manufacturer documents U300E publicly. A real wiring fault usually leaves functions on that feed dead with the engine running, which helps to separate the two cases.
- What you may notice
- Functions on the run-only feed dead with the engine running
- Code logged right after each start with no other complaint
- Likely causes
- PossibleBlown fuse or faulty run relay on the run-only feed
- PossibleInput wire open, shorted or backfed
- PossibleModule software misjudging the intended drop during cranking
- RareWorn run contact in the ignition switch
- Repair
- Medium · Often possible to do yourself.Typical cost: €20 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.