Code
U300C
Generic
U — Network/User
Ignition Input Off/On/Start
Views:
UK: 20
EN: 31
RU: 18
AI status
Completed
Completed
100%
Causes
- Faulty ignition switch or key cylinder
- Open or shorted wiring between ignition switch and control module
- Blown fuse or faulty ignition relay
- Corroded or loose connector at the module or switch
- Intermittent battery/ground or low battery voltage during cranking
- Faulty body/control module or input circuit
Symptoms
- Engine cranks intermittently or no crank/no start
- Accessories may not turn on in Run or behave incorrectly
- Starter engages unexpectedly or does not engage when Start is requested
- Malfunction indicator lamp may be on or diagnostic trouble lamp illuminated
- Intermittent loss of vehicle systems dependent on correct ignition state
What to check
- Read freeze frame and live data: note recorded ignition input state for Off/Run/Start
- Verify battery voltage at rest and during cranking (expected ~12.6 V at rest, ≥9–11 V during cranking)
- Inspect ignition switch and connector for corrosion, damage, or loose pins
- Check relevant fuses and ignition relay operation
- Backprobe ignition input pin at the affected module and observe voltage while cycling key Off/Run/Start
- Perform wiggle test of wiring harness while monitoring ignition input signal for intermittent changes
Signal parameters
- Ignition Off: single‑ended input ≈ 0–0.5 V (or logical LOW)
- Ignition Run/On: single‑ended input ≈ battery voltage (≈ 11–14 V) under normal battery condition
- Ignition Start: input should go to Run level and remain or show a distinct Start flag; battery voltage will drop during cranking (commonly 9–11 V)
- Tolerance: voltage may vary with battery condition; intermittent or floating values indicate wiring/connector faults
- CAN network: if ignition state is delivered via CAN, expect regular messages with correct ID and payload; CAN recessive ≈ 2.5 V, dominant differential levels ~1.5–3.5 V
Diagnostic algorithm
- Verify the code: connect a scan tool, confirm U300C is current or historical and note freeze frame data and ignition state recorded.
- Check battery and ground: confirm good battery voltage and secure, clean grounds before further testing.
- Inspect fuses/relays: verify ignition and starter fuses and relays are present and functioning.
- Observe live data: monitor the ignition input parameter while cycling key Off → Run → Start. Note expected voltage transitions.
- Backprobe and measure: with meter or scope, measure voltage at the module ignition input pin and at the ignition switch output while operating the key; compare readings.
- Wiggle test harness: with meter/scope connected, wiggle wiring and connectors between switch and module to find intermittent faults.
- Check connector and pins: disconnect connectors and inspect for corrosion, bent pins, water intrusion, or poor pin retention; repair as needed.
- Verify network messages: if ignition state is sent over CAN, use a scope or scanner to confirm message presence and correct payload; repair bus faults as needed.
- Repair wiring or switch faults: repair splices, replace damaged harness sections, or replace ignition switch if internal contacts fail.
- If wiring and switch are good, consider module fault: update module software if available, reflash, or replace the control module only after ruling out wiring and power/ground.
- Clear the code and perform re-test: erase codes, operate vehicle through multiple key cycles and a road test if necessary to confirm the fault does not return.
Likely causes
- Ignition switch contact wear or internal failure preventing proper Off/Run/Start signals
- Pinched or damaged harness conductor to the ignition input pin on the module
- Corroded connector terminal at ignition switch or module
- Blown ignition fuse or failed starter/ignition relay
- Intermittent module input circuit due to water intrusion or broken solder joint
- ECU/BCM firmware or internal fault incorrectly interpreting ignition state
Fault status
Status
Ignition input Off/On/Start signal invalid or not detected by control module. Check ignition switch, wiring, fuses/relays, module input, and network messages.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
U300C
HYUNDAI
U — Network/User
Ignition Input Off/On/Start
Views:
UK: 10
EN: 24
RU: 15
AI status
Completed
Completed
100%
Causes
- Faulty ignition switch or key cylinder
- Open or shorted wiring between ignition switch and control module
- Blown fuse or faulty ignition relay
- Corroded or loose connector at the module or switch
- Intermittent battery/ground or low battery voltage during cranking
- Faulty body/control module or input circuit
Symptoms
- Engine cranks intermittently or no crank/no start
- Accessories may not turn on in Run or behave incorrectly
- Starter engages unexpectedly or does not engage when Start is requested
- Malfunction indicator lamp may be on or diagnostic trouble lamp illuminated
- Intermittent loss of vehicle systems dependent on correct ignition state
What to check
- Read freeze frame and live data: note recorded ignition input state for Off/Run/Start
- Verify battery voltage at rest and during cranking (expected ~12.6 V at rest, ≥9–11 V during cranking)
- Inspect ignition switch and connector for corrosion, damage, or loose pins
- Check relevant fuses and ignition relay operation
- Backprobe ignition input pin at the affected module and observe voltage while cycling key Off/Run/Start
- Perform wiggle test of wiring harness while monitoring ignition input signal for intermittent changes
Signal parameters
- Ignition Off: single‑ended input ≈ 0–0.5 V (or logical LOW)
- Ignition Run/On: single‑ended input ≈ battery voltage (≈ 11–14 V) under normal battery condition
- Ignition Start: input should go to Run level and remain or show a distinct Start flag; battery voltage will drop during cranking (commonly 9–11 V)
- Tolerance: voltage may vary with battery condition; intermittent or floating values indicate wiring/connector faults
- CAN network: if ignition state is delivered via CAN, expect regular messages with correct ID and payload; CAN recessive ≈ 2.5 V, dominant differential levels ~1.5–3.5 V
Diagnostic algorithm
- Verify the code: connect a scan tool, confirm U300C is current or historical and note freeze frame data and ignition state recorded.
- Check battery and ground: confirm good battery voltage and secure, clean grounds before further testing.
- Inspect fuses/relays: verify ignition and starter fuses and relays are present and functioning.
- Observe live data: monitor the ignition input parameter while cycling key Off → Run → Start. Note expected voltage transitions.
- Backprobe and measure: with meter or scope, measure voltage at the module ignition input pin and at the ignition switch output while operating the key; compare readings.
- Wiggle test harness: with meter/scope connected, wiggle wiring and connectors between switch and module to find intermittent faults.
- Check connector and pins: disconnect connectors and inspect for corrosion, bent pins, water intrusion, or poor pin retention; repair as needed.
- Verify network messages: if ignition state is sent over CAN, use a scope or scanner to confirm message presence and correct payload; repair bus faults as needed.
- Repair wiring or switch faults: repair splices, replace damaged harness sections, or replace ignition switch if internal contacts fail.
- If wiring and switch are good, consider module fault: update module software if available, reflash, or replace the control module only after ruling out wiring and power/ground.
- Clear the code and perform re-test: erase codes, operate vehicle through multiple key cycles and a road test if necessary to confirm the fault does not return.
Likely causes
- Ignition switch contact wear or internal failure preventing proper Off/Run/Start signals
- Pinched or damaged harness conductor to the ignition input pin on the module
- Corroded connector terminal at ignition switch or module
- Blown ignition fuse or failed starter/ignition relay
- Intermittent module input circuit due to water intrusion or broken solder joint
- ECU/BCM firmware or internal fault incorrectly interpreting ignition state
Fault status
Status
Ignition input Off/On/Start signal invalid or not detected by control module. Check ignition switch, wiring, fuses/relays, module input, and network messages.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
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