Code
U300A
HYUNDAI
U — Network/User
Ignition Switch
Views:
UK: 12
EN: 20
RU: 17
AI status
Completed
Completed
100%
Causes
- Faulty ignition switch or ignition switch module
- Damaged wiring or poor connection at ignition switch connector
- Blown fuse or faulty relay supplying ignition switch circuits
- Low battery voltage or poor battery/ground connections
- Intermittent connector/corrosion/short to ground or battery
- Faulty Body Control Module (BCM), Integrated Power Module, or other network module
Symptoms
- No-crank or intermittent crank condition
- Engine will not start or starts intermittently
- Instrument cluster/AVN shows incorrect ignition position or warning messages
- Accessory power not working in ACC/ON positions
- Fail-safe / limp mode or reduced functionality of some systems
- Erratic behavior of electronics tied to ignition state (locks, windows, HVAC)
What to check
- Read and record all stored codes and freeze frame data from all modules with a capable scan tool
- Verify battery voltage and battery ground connections (measure with engine off and during cranking)
- Inspect ignition switch connector and harness for damage, corrosion, or loose pins
- Check related fuses and ignition relays for continuity and proper operation
- Monitor ignition switch status signal(s) with a scan tool while operating key positions (ACC/ON/START)
- Perform wiggle test of harness while monitoring signal to look for intermittent faults
Signal parameters
- Ignition switch outputs: expected ~0 V (OFF) or ~12 V (ACC/ON/START) depending on position
- Starter (ST) output is a switched 12 V signal active only in START position
- IG1/IG2 circuits: 0 V (OFF) to battery voltage (ON); measure for stable voltage with key positions
- Signal update rate: ignition status reported periodically on vehicle network (CAN/LIN); absence or invalid messages flagged
- Typical expected CAN/LIN: normal bus voltage ~2.5 V idle (CAN transceivers) and proper message traffic; watch for bus errors
Diagnostic algorithm
- Verify the customer complaint and attempt to reproduce the symptom. Note key positions and any module warnings.
- Scan all control modules, save U300A and any related codes (communication or power). Inspect freeze frame/live data for ignition status entries.
- Check battery voltage (should be ~12.4–12.8 V at rest). Charge or replace battery if low and retest.
- Visually inspect ignition switch and harness for damage, corrosion, pin push-out, or water ingress; repair any wiring issues.
- With a DVOM or oscilloscope, probe ignition switch terminals and verify correct voltages in each key position (ACC/ON/START).
- Check continuity to modules that receive ignition status (BCM/IPCM/instrument cluster). Repair open/short circuits as needed.
- Verify related fuses and relays and replace if suspect. Swap known-good relay if available to confirm.
- Monitor bus messages and module responses with a capable scan tool—look for lost communication or invalid ignition status messages.
- If wiring and power are good but signal still missing, consider replacing the ignition switch assembly. Retest and clear codes.
- If fault persists after ignition switch replacement, test/replace the receiving module (BCM/IPC) only after confirming wiring and power are correct.
Likely causes
- Open or shorted ignition switch harness (IG1/IG2/ACC/ST)
- Corroded or loose connector at ignition switch
- Failed ignition switch internal contacts
- Related fuse or ignition relay failed
- Module that reads ignition status (BCM/IPC) not receiving signal due to wiring or module fault
Fault status
Status
Ignition switch signal missing or invalid. Modules report loss or out-of-range ignition status which can prevent starting or cause erratic accessory behavior. Further diagnosis of switch, wiring, fuses/relays, and network communication required.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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