Code
C1603
HYUNDAI
C — Chassis
L’ Line | EPS Thermal Protection | ECU Internal Thermal & Voltage Error | Derating (EPS Thermal Protection) | ECU thermal protection
Views:
UK: 17
EN: 42
RU: 21
AI status
Completed
Completed
100%
Causes
- EPS control unit internal over-temperature detection
- Low or unstable supply voltage to the EPS ECU
- Excessive motor current or overload condition
- Poor battery condition or weak charging system
- Damaged wiring, poor connector/ground connections, or water intrusion
- Faulty EPS ECU internal sensor or ECU hardware fault
Symptoms
- EPS warning light or EPS malfunction message on dash
- Reduced or totally lost power steering assist (heavy steering feel)
- Intermittent assist that returns after cooling or vehicle shutdown
- Steering effort increases during prolonged low-speed steering
- Possible unusual noise from EPS motor or control unit
- No driveability/engine symptoms aside from EPS warnings
What to check
- Read and record C1603 plus any other stored/registered codes and freeze frame data
- Check battery voltage at rest and while cranking; check alternator charging voltage
- Visually inspect EPS ECU connector, wiring harness, and grounds for damage, corrosion, or water ingress
- Inspect steering column and rack for mechanical binding or obstruction
- Monitor in real time: EPS ECU internal temperature, motor current, supply voltage, CAN communication
- Check for related CAN communication codes (U-codes) that may indicate bus issues
Signal parameters
- Battery/Supply Voltage to EPS ECU: typically ~12–14.5 V (varies by system); drops under load indicate charging/battery issues
- EPS ECU Internal Temperature: should remain below manufacturer threshold; rising into protection range triggers C1603
- Motor Current / Output Current: elevated values during overload or fault
- Motor Temperature (if available): elevated after repeated heavy steering
- Steering Torque Sensor Signal: valid torque sensor values and no saturation
- CAN BUS: EPS status messages present and valid (no communication loss)
Diagnostic algorithm
- Connect a capable scan tool; read and save all DTCs and freeze frame data. Note operating conditions when C1603 set (vehicle speed, battery voltage, steering events).
- Clear codes and attempt to reproduce fault under similar conditions (low-speed repeated turning, parking maneuvers). Observe if derating or fault returns.
- Check battery and charging system: measure open-circuit voltage, voltage under load, and alternator output. Replace or charge battery if low.
- Inspect EPS power supply and ground circuits: verify fuses, relays, connector pin condition, and continuity to battery and chassis ground.
- Perform visual inspection of EPS unit and harness for signs of water intrusion, corrosion, burned wires, or connector damage.
- Monitor live data while operating steering: supply voltage to EPS, ECU internal temp, motor current, and torque sensor readings. Compare to expected ranges.
- If high motor current or overheating is observed, inspect steering linkage and rack for binding, foreign objects, or worn components causing excessive load.
- Check for CAN communication faults and related modules; repair any bus faults before replacing EPS components.
- Review manufacturer service information for software updates or ECU reflash procedures; apply updates if recommended.
- If electrical supply, wiring, and mechanical causes are ruled out and internal ECU thermal/voltage protection still triggers, consider replacing the EPS control module per service procedures.
- After repair, clear codes and perform a thorough test drive to verify the issue is resolved and no recurrence of derating occurs.
Likely causes
- High EPS motor temperature after prolonged heavy steering or repeated low-speed maneuvers
- Battery voltage dropping under load (weak battery or failing alternator)
- High resistance in power/ground wiring to EPS causing voltage drop
- Shorted motor windings or mechanical binding in steering system causing overcurrent
- Corroded/wet connector at EPS ECU causing intermittent voltage spikes
- Internal ECU electronics failure or inaccurate internal temperature sensor
Fault status
Status
EPS ECU detected internal temperature or voltage outside safe operating range. To protect the system, the EPS may reduce or disable power assist (thermal/voltage protection). Service is required to identify and correct the cause.
Repair difficulty: Medium
Diagnostic time: 1.0 - 3.0 hours
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