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Home / DTC / C1705 — ECU Pre-Charge Circuit Fail | ECU Precharge Circuit Fault

C1705 — ECU Pre-Charge Circuit Fail | ECU Precharge Circuit Fault

Detailed page for trouble code C1705.

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C1705

HYUNDAI C — Chassis

ECU Pre-Charge Circuit Fail | ECU Precharge Circuit Fault

Brand: HYUNDAI
Type: C — Chassis
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted pre‑charge resistor (bleeder)
  • Faulty pre‑charge relay/contactor or relay coil driver
  • Wiring harness damage, corrosion, or poor connector contact in pre‑charge circuit
  • Blown fuse or fusible link supplying the pre‑charge circuit
  • ECU driver transistor or internal ECU fault
  • High‑voltage battery / BMS refusing pre‑charge (low voltage, fault, or communication error)

Symptoms

  • Malfunction Indicator Lamp / MIL, or dedicated hybrid/EV warning lamps illuminated
  • Vehicle fails to complete HV system startup (READY lamp off) or refuses to enter drive mode
  • Long crank/no‑drive or immediate limp/inhibit of propulsion on vehicles with hybrid/EV systems
  • Audible relay chatter or no relay click from pre‑charge/contactors during key‑on
  • Diagnostic trouble codes present related to pre‑charge / high‑voltage system

What to check

  • Observe safety: follow manufacturer high‑voltage lockout and PPE procedures before any HV inspection
  • Connect a capable scan tool; read all stored/continuous codes and live data related to pre‑charge and HV system
  • With proper safety/isolation, visually inspect pre‑charge relay/contactor, wiring harnesses and connectors for corrosion, heat damage or loose pins
  • Check fuses/fusible links supplying the pre‑charge circuit and ECU driver circuits
  • Monitor pre‑charge voltage ramp (across pre‑charge resistor or HV bus) during key‑on and record time to reach near battery voltage
  • Check continuity and resistance of pre‑charge resistor (when isolated) and contactor/relay coil resistance (when de‑energized)

Signal parameters

  • Typical control output: 0V (off) / ~12V (on) for relay coil or logic PWM from ECU (varies by model)
  • Expected pre‑charge voltage ramp: HV bus voltage should rise smoothly toward HV battery voltage within ~1–5 seconds (vehicle dependent)
  • Pre‑charge resistor DC resistance: often tens to hundreds of ohms (model dependent) — compare to spec
  • Contactor/relay coil resistance: typically a few ohms to tens of ohms — compare to spec
  • If available, ECU live data: pre‑charge command status (ON/OFF), pre‑charge elapsed time, HV battery pack voltage

Diagnostic algorithm

  1. Safety first — disable/isolated high‑voltage system per manufacturer procedure and wear appropriate PPE.
  2. Use scan tool to record the active/frozen data and all C/P codes; note freeze frame and any HV/BMS codes that accompany C1705.
  3. With HV system disabled, visually inspect pre‑charge resistor, relay/contactor, wiring harness, and connectors for damage, burns, or corrosion. Repair visible faults.
  4. Check all related fuses and fusible links; replace if blown and investigate cause.
  5. With HV isolated, measure continuity and resistance of pre‑charge resistor and contactor/relay coil; compare to specs. Replace component if out of tolerance.
  6. Re‑enable low‑voltage system and monitor relay coil control: energize pre‑charge (key ON or commanded by scan tool) and verify control voltage to coil and ground continuity. If control output absent, suspect ECU/driver or wiring.
  7. With instruments and following HV safety, command pre‑charge and measure HV bus voltage ramp across the pre‑charge resistor; verify ramp time and that contactor closes only after proper pre‑charge level reached.
  8. If pre‑charge control output is present but circuit does not behave, isolate and bench‑test relay/contactor and replace as needed.
  9. If wiring and components check good but fault persists, consider ECU/driver module fault or software; consult manufacturer service information for ECU tests, reprogramming or replacement procedures.
  10. After repairs, clear codes, perform full system relearn/startup procedure per manufacturer, verify HV system ready status, and road test while monitoring for return of fault.

Likely causes

  • Pre‑charge relay coil not energizing due to open coil, blown fuse, or lost ground
  • Pre‑charge resistor open/altered value preventing expected voltage ramp
  • Control output from ECU not switching (failed driver)
  • Connector corrosion at relay or HV junction causing intermittent/open circuit
  • HV battery BMS inhibiting pre‑charge because of internal fault or low state of charge

Fault status

⚠️ Status
ECU detected failure in pre‑charge circuit — pre‑charge not achieved within expected time or circuit open/short detected. HV pre‑charge sequence incomplete; vehicle may inhibit HV system.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

C1700 C1701 C1704 P0A0F C1234
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

HYUNDAI

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Code

C1705

LAND ROVER C — Chassis

Left rear central sensor - short circuit to the battery

Brand: LAND ROVER
Type: C — Chassis
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted pre‑charge resistor (bleeder)
  • Faulty pre‑charge relay/contactor or relay coil driver
  • Wiring harness damage, corrosion, or poor connector contact in pre‑charge circuit
  • Blown fuse or fusible link supplying the pre‑charge circuit
  • ECU driver transistor or internal ECU fault
  • High‑voltage battery / BMS refusing pre‑charge (low voltage, fault, or communication error)

Symptoms

  • Malfunction Indicator Lamp / MIL, or dedicated hybrid/EV warning lamps illuminated
  • Vehicle fails to complete HV system startup (READY lamp off) or refuses to enter drive mode
  • Long crank/no‑drive or immediate limp/inhibit of propulsion on vehicles with hybrid/EV systems
  • Audible relay chatter or no relay click from pre‑charge/contactors during key‑on
  • Diagnostic trouble codes present related to pre‑charge / high‑voltage system

What to check

  • Observe safety: follow manufacturer high‑voltage lockout and PPE procedures before any HV inspection
  • Connect a capable scan tool; read all stored/continuous codes and live data related to pre‑charge and HV system
  • With proper safety/isolation, visually inspect pre‑charge relay/contactor, wiring harnesses and connectors for corrosion, heat damage or loose pins
  • Check fuses/fusible links supplying the pre‑charge circuit and ECU driver circuits
  • Monitor pre‑charge voltage ramp (across pre‑charge resistor or HV bus) during key‑on and record time to reach near battery voltage
  • Check continuity and resistance of pre‑charge resistor (when isolated) and contactor/relay coil resistance (when de‑energized)

Signal parameters

  • Typical control output: 0V (off) / ~12V (on) for relay coil or logic PWM from ECU (varies by model)
  • Expected pre‑charge voltage ramp: HV bus voltage should rise smoothly toward HV battery voltage within ~1–5 seconds (vehicle dependent)
  • Pre‑charge resistor DC resistance: often tens to hundreds of ohms (model dependent) — compare to spec
  • Contactor/relay coil resistance: typically a few ohms to tens of ohms — compare to spec
  • If available, ECU live data: pre‑charge command status (ON/OFF), pre‑charge elapsed time, HV battery pack voltage

Diagnostic algorithm

  1. Safety first — disable/isolated high‑voltage system per manufacturer procedure and wear appropriate PPE.
  2. Use scan tool to record the active/frozen data and all C/P codes; note freeze frame and any HV/BMS codes that accompany C1705.
  3. With HV system disabled, visually inspect pre‑charge resistor, relay/contactor, wiring harness, and connectors for damage, burns, or corrosion. Repair visible faults.
  4. Check all related fuses and fusible links; replace if blown and investigate cause.
  5. With HV isolated, measure continuity and resistance of pre‑charge resistor and contactor/relay coil; compare to specs. Replace component if out of tolerance.
  6. Re‑enable low‑voltage system and monitor relay coil control: energize pre‑charge (key ON or commanded by scan tool) and verify control voltage to coil and ground continuity. If control output absent, suspect ECU/driver or wiring.
  7. With instruments and following HV safety, command pre‑charge and measure HV bus voltage ramp across the pre‑charge resistor; verify ramp time and that contactor closes only after proper pre‑charge level reached.
  8. If pre‑charge control output is present but circuit does not behave, isolate and bench‑test relay/contactor and replace as needed.
  9. If wiring and components check good but fault persists, consider ECU/driver module fault or software; consult manufacturer service information for ECU tests, reprogramming or replacement procedures.
  10. After repairs, clear codes, perform full system relearn/startup procedure per manufacturer, verify HV system ready status, and road test while monitoring for return of fault.

Likely causes

  • Pre‑charge relay coil not energizing due to open coil, blown fuse, or lost ground
  • Pre‑charge resistor open/altered value preventing expected voltage ramp
  • Control output from ECU not switching (failed driver)
  • Connector corrosion at relay or HV junction causing intermittent/open circuit
  • HV battery BMS inhibiting pre‑charge because of internal fault or low state of charge

Fault status

⚠️ Status
ECU detected failure in pre‑charge circuit — pre‑charge not achieved within expected time or circuit open/short detected. HV pre‑charge sequence incomplete; vehicle may inhibit HV system.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

C1700 C1701 C1704 P0A0F C1234
413

Browse 413 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

C1705

Other C — Chassis

Left Rear Center Sensor Circuit Short to Vbat

Brand: Other
Type: C — Chassis
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Open or shorted pre‑charge resistor (bleeder)
  • Faulty pre‑charge relay/contactor or relay coil driver
  • Wiring harness damage, corrosion, or poor connector contact in pre‑charge circuit
  • Blown fuse or fusible link supplying the pre‑charge circuit
  • ECU driver transistor or internal ECU fault
  • High‑voltage battery / BMS refusing pre‑charge (low voltage, fault, or communication error)

Symptoms

  • Malfunction Indicator Lamp / MIL, or dedicated hybrid/EV warning lamps illuminated
  • Vehicle fails to complete HV system startup (READY lamp off) or refuses to enter drive mode
  • Long crank/no‑drive or immediate limp/inhibit of propulsion on vehicles with hybrid/EV systems
  • Audible relay chatter or no relay click from pre‑charge/contactors during key‑on
  • Diagnostic trouble codes present related to pre‑charge / high‑voltage system

What to check

  • Observe safety: follow manufacturer high‑voltage lockout and PPE procedures before any HV inspection
  • Connect a capable scan tool; read all stored/continuous codes and live data related to pre‑charge and HV system
  • With proper safety/isolation, visually inspect pre‑charge relay/contactor, wiring harnesses and connectors for corrosion, heat damage or loose pins
  • Check fuses/fusible links supplying the pre‑charge circuit and ECU driver circuits
  • Monitor pre‑charge voltage ramp (across pre‑charge resistor or HV bus) during key‑on and record time to reach near battery voltage
  • Check continuity and resistance of pre‑charge resistor (when isolated) and contactor/relay coil resistance (when de‑energized)

Signal parameters

  • Typical control output: 0V (off) / ~12V (on) for relay coil or logic PWM from ECU (varies by model)
  • Expected pre‑charge voltage ramp: HV bus voltage should rise smoothly toward HV battery voltage within ~1–5 seconds (vehicle dependent)
  • Pre‑charge resistor DC resistance: often tens to hundreds of ohms (model dependent) — compare to spec
  • Contactor/relay coil resistance: typically a few ohms to tens of ohms — compare to spec
  • If available, ECU live data: pre‑charge command status (ON/OFF), pre‑charge elapsed time, HV battery pack voltage

Diagnostic algorithm

  1. Safety first — disable/isolated high‑voltage system per manufacturer procedure and wear appropriate PPE.
  2. Use scan tool to record the active/frozen data and all C/P codes; note freeze frame and any HV/BMS codes that accompany C1705.
  3. With HV system disabled, visually inspect pre‑charge resistor, relay/contactor, wiring harness, and connectors for damage, burns, or corrosion. Repair visible faults.
  4. Check all related fuses and fusible links; replace if blown and investigate cause.
  5. With HV isolated, measure continuity and resistance of pre‑charge resistor and contactor/relay coil; compare to specs. Replace component if out of tolerance.
  6. Re‑enable low‑voltage system and monitor relay coil control: energize pre‑charge (key ON or commanded by scan tool) and verify control voltage to coil and ground continuity. If control output absent, suspect ECU/driver or wiring.
  7. With instruments and following HV safety, command pre‑charge and measure HV bus voltage ramp across the pre‑charge resistor; verify ramp time and that contactor closes only after proper pre‑charge level reached.
  8. If pre‑charge control output is present but circuit does not behave, isolate and bench‑test relay/contactor and replace as needed.
  9. If wiring and components check good but fault persists, consider ECU/driver module fault or software; consult manufacturer service information for ECU tests, reprogramming or replacement procedures.
  10. After repairs, clear codes, perform full system relearn/startup procedure per manufacturer, verify HV system ready status, and road test while monitoring for return of fault.

Likely causes

  • Pre‑charge relay coil not energizing due to open coil, blown fuse, or lost ground
  • Pre‑charge resistor open/altered value preventing expected voltage ramp
  • Control output from ECU not switching (failed driver)
  • Connector corrosion at relay or HV junction causing intermittent/open circuit
  • HV battery BMS inhibiting pre‑charge because of internal fault or low state of charge

Fault status

⚠️ Status
ECU detected failure in pre‑charge circuit — pre‑charge not achieved within expected time or circuit open/short detected. HV pre‑charge sequence incomplete; vehicle may inhibit HV system.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 1.5-3.0 hours

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