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DTC codes / U30xx · Network wiring and bus faults / U302F

U302FIgnition Output Accessory

U302F is a generic network code indicating that a control module has detected a fault on the ignition output accessory circuit, which is the switched power feed that enables accessory components only when the ignition is in the accessory or run position. The computer monitors this circuit for abnormal voltage or current and sets the code when the expected signal is missing or out of range.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork wiring and bus faults

Symptoms you may notice

  • The warning light (check engine or service vehicle soon) illuminates on the dashboard.
  • Accessory devices such as the radio, power outlets, or interior lighting may not work when the ignition is in the accessory position.
  • Intermittent operation of accessories, especially over bumps or when turning the key.
  • The vehicle may fail to start or have a no-crank condition if the ignition switch output is completely dead.
  • Often no symptoms besides the warning light, especially if the fault is intermittent or affects a non-critical accessory.

Common causes, most likely first

  1. Faulty ignition switch or ignition cylinder, causing poor contact in the accessory position.
  2. Blown fuse or fusible link in the ignition accessory circuit.
  3. Damaged wiring or corroded connector in the ignition output accessory circuit, often due to chafing or moisture.
  4. Failed body control module (BCM) or ignition control module that manages the accessory output.
  5. Aftermarket accessories improperly wired into the ignition accessory circuit, causing excessive current draw or backfeeding.
  6. Loose or corroded battery terminals or ground connections affecting voltage supply to the ignition switch.

How to diagnose and fix it

  1. Verify the battery is fully charged and terminals are clean and tight; a weak battery can cause false ignition circuit codes.
  2. Check all fuses related to the ignition accessory circuit, including underhood and interior fuse boxes, and replace any blown fuse.
  3. Inspect the ignition switch for wear or loose connections; test for voltage at the accessory output terminal in the accessory and run positions.
  4. Trace the wiring from the ignition switch to the accessory components, looking for chafed wires, corrosion, or loose connectors.
  5. Test the body control module (BCM) or ignition control module for proper operation and communication; check for related codes in other modules.
  6. If the fault is intermittent, perform a wiggle test on the ignition switch and wiring while monitoring the circuit with a multimeter or scan tool.
  7. Clear the code and test-drive the vehicle to confirm the repair; if the code returns, re-evaluate the circuit with a wiring diagram specific to the vehicle.

Ignition Switch Wear and Hidden Circuit Faults

  • A worn ignition switch often causes this code without any obvious starting problem because the accessory contacts wear out before the start contacts.
  • Aftermarket alarms, remote starters, or phone chargers plugged into the accessory socket can backfeed voltage and set U302F intermittently.
  • The code can be set by a low battery or poor ground even if the ignition circuit itself is healthy, so always load-test the battery first.
  • Some vehicles set U302F when the ignition switch is left in the accessory position too long with the engine off, draining the battery and causing voltage drop.
  • A faulty body control module (BCM) may set this code along with other communication codes, so check for related U-codes before replacing the BCM.

Can I keep driving with U302F?

If the vehicle starts and runs normally, you can drive it to a repair shop, but avoid using accessory functions that may be affected. If the engine cranks but does not start or the ignition switch feels loose, stop driving and have the vehicle towed to prevent a no-start condition.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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