U302BIgnition Output Accessory/On/Start
- Generic OBD-II code · Network
- How the car detects it
- U302B belongs to the ignition outputs, i.e. a feed that a module switches itself instead of merely reading it. The Accessory/On/Start variant should carry voltage in every power mode except Off and, unlike most accessory feeds, should stay on while the engine cranks. The driving unit, typically a body controller or the power supply unit of a keyless start system, compares its command with what it reads back on its own pin and stores U302B when the two differ: voltage in Off, or none in accessory, run or crank. No manufacturer documents U302B publicly. Tokai Rika's patent US6900552B2 shows such a unit switching separate relay coils for accessory, two ignition stages and the starter through FET drivers. A driver stuck on or a welded relay contact on this feed can flatten the battery overnight.
- What you may notice
- Battery flat after the car has been parked
- Several loads on the feed dead although the vehicle is switched on
- Warning about the power supply or ignition system in the cluster
- Likely causes
- PossibleWelded relay contact keeping the feed live in Off
- PossibleFaulty driver stage in the switching module, stuck on or not switching
- PossibleOutput wire or a connected load shorted to ground, tripping the driver protection
- RareBlown fuse between the relay and the loads on this feed
- Repair
- Medium · Usually a job for a workshop.Typical cost: €20 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.