Code
U300C
HYUNDAI
U — Network/User
Ignition Input Off/On/Start
Views:
UK: 10
EN: 23
RU: 15
AI status
Completed
Completed
100%
Causes
- Faulty ignition switch or key cylinder
- Damaged wiring or chafed harness in steering column/ignition circuit
- Loose, corroded or pushed‑out connector at ignition switch or BCM
- Blown fuse or faulty ignition/start relay
- Intermittent battery/low system voltage
- Faulty Body Control Module (BCM) or other network module
Symptoms
- MIL or warning lamp illuminated for network/ignition error
- Car won’t crank or intermittent no‑crank condition
- Starter engages only intermittently or only in certain key positions
- Instrument cluster displays incorrect ignition position (e.g., shows OFF when key is ON)
- Accessories may not power correctly or switch on/off unexpectedly
- Vehicle may stall or refuse to enter RUN/START modes
What to check
- Read and record U300C and any other stored codes and freeze‑frame data with a diagnostic scanner
- Check battery voltage (engine off): should be ~12.4–12.8 V; during cranking >9.5 V
- Visually inspect fuses and ignition/start relays related to IGN/ACC/START circuits
- Inspect wiring and connectors at the ignition switch/steering column and at the BCM for corrosion, damage, or loose pins
- Check for other network/communication codes (U0100, U0401, etc.)
- Attempt to reproduce problem while monitoring scanner for ignition state changes
Signal parameters
- Ignition OFF: input ≈ 0 V (or low logic level) to the receiving module
- Ignition ON/RUN: input ≈ battery voltage (~12 V nominal) present at RUN terminal
- Ignition START: START terminal ≈ battery voltage only during cranking (short duration)
- Transition behavior: clean, single transition OFF→ON→START; no rapid switching, bouncing, or floating voltages
- CAN/serial message: module should report ignition state consistent with physical switch (check with scanner)
Diagnostic algorithm
- Connect a capable scan tool; document U300C and any related codes and freeze‑frame data.
- Verify battery condition and system voltage. Charge battery or connect known good battery if voltage low; recheck code.
- With key in OFF/ON/START positions, measure voltage at ignition switch harness pins and at the corresponding BCM connector pins. Compare voltages to expected signal_params.
- If voltages at the switch are correct but not present at the BCM, perform continuity check and inspect wiring between switch and BCM for opens/shorts; repair any damaged wiring.
- If voltages are incorrect at the switch, remove steering column cover and inspect ignition switch connector and switch assembly. Wiggle test while observing voltages for intermittent faults.
- Inspect/replace related fuses and relays. Check grounds for tightness and corrosion at chassis and engine grounds.
- Scan the CAN/network for communication faults; inspect CAN high/low wiring and connectors if bus errors are present.
- If wiring and power are good and problem persists, consider BCM reprogramming or replacement after confirming with manufacturer bulletins/technical service info.
- Clear codes and retest under the same conditions to confirm repair. If intermittent, road test to recreate and verify stability.
Likely causes
- Worn/failing ignition switch contacts
- Open/short in ignition harness between switch and BCM
- Loose connector at the steering column or BCM
- Low battery voltage or poor main ground
- BCM software bug or module failure
Fault status
Status
Ignition Input Off/On/Start — ignition position signal missing, incorrect or inconsistent; stored by control module when ignition input behavior is invalid or not communicated correctly.
Repair difficulty: Medium
Diagnostic time: 1.0 - 2.5 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email