U302B code meaning
Ignition Output Accessory/On/Start
What U302B means
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.
U302B at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U302B
- 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
Common causes of U302B
- 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
- Less likelyBlown fuse between the relay and the loads on this feed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Ignition outputIgnition relayOutput wiring
What each part of U302B means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 2B | The exact fault in that area. |
What to do next
- Note U302B 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 U302B
What does U302B mean?
U302B means "Ignition Output Accessory/On/Start". U302B belongs to the ignition outputs, i.e. It is a generic code, so it means the same on every make.
Is it safe to drive with U302B?
U302B does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U302B fail an emissions test?
U302B 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 U302B to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will U302B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.