U300F

Code

Generic U — Network/User

Ignition Input Accessory

Brand: Generic

Type: U — Network/User

Views: UK: 25 EN: 28 RU: 20

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Blown or corroded fuse for ignition/accessory circuit
Faulty ignition switch or ignition lock cylinder
Open or shorted wiring between ignition switch and body control module (BCM)/instrument cluster
Poor or missing ground at BCM or related module
Faulty BCM/IPC or other module input circuit
Aftermarket accessory wiring interfering with ACC circuit

Accessory electronics (radio, infotainment, power outlets) do not power in ACC position
Incorrect ignition state reported by dash (ACC not detected when key is in ACC)
Intermittent or no crank if ACC/RUN signals misreported
Warning lights or communication faults on the instrument cluster
Possible battery drain if ACC circuit is stuck on

Scan vehicle and save freeze-frame and live data; confirm U300F is current and note ignition state reported by modules
Verify related fuses and relays for ignition/accessory circuits are intact and properly seated
Visually inspect ignition switch connector, BCM connector, and harness for corrosion, bent pins, or damage
Check module power and ground integrity (voltage and continuity)
Attempt to reproduce fault with key in OFF/ACC/RUN/START while monitoring ACC input at module
Inspect for recent aftermarket installs that tap ACC circuit (alarms, stereos)

Signal type: Switched battery feed (key-switched accessory feed) into module input
Expected voltage: OFF ~ 0 V; ACC active ≈ 9–13.5 V (battery voltage minus drops); RUN/START also ≈ 9–13.5 V on related circuits
Threshold guidance: ACC considered active if > ~8 V; inactive if < ~2–3 V
Typical input impedance: low-impedance switched feed; continuity from switch to module should be near 0 ohms (wiring < 5 ohms)
Short conditions: short to ground will show near 0 V; short to battery will show constant battery voltage regardless of key position

Retrieve codes and live data. Confirm ignition position reported by the module and whether ACC input toggles with key.
Check fuses and relays for the ACC/IGN circuits; replace any blown fuses and retest.
With a DVOM, measure voltage at the ignition switch ACC terminal and at the BCM/input pin with key in OFF/ACC/RUN. Note differences.
If ACC voltage present at the switch but missing at the module, test continuity between switch and module connector. Repair open or high-resistance wiring.
Inspect and back-probe connectors for corrosion, bent pins, or intermittent contact. Wiggle test harness while observing live data for intermittent faults.
Check grounds for BCM and related modules; measure resistance to chassis (
If wiring and external components are good, perform bench or directed module input test per manufacturer procedure or consult service manual for BCM input diagnostics.
Check for related diagnostic trouble codes (communication or power codes) and apply any known software updates or recalibration for modules.
After repairs, clear codes and verify ACC behavior over several key cycles and during a short drive or use period to confirm the issue is resolved.