Code
C1123
HYUNDAI
C — Chassis
Sensor 3 Battery Voltage Low | Rear Left Sensor Battery Voltage Low
Views:
UK: 13
EN: 20
RU: 14
AI status
Completed
Completed
100%
Causes
- Aging or depleted TPMS sensor battery (most common)
- Physical damage to the sensor or valve stem
- Corrosion or loose valve hardware preventing contact (if sensor uses valve-mounted contacts)
- Receiver/antenna fault or poor RF reception at that wheel position
- Sensor not learned or wrong sensor ID after wheel/tire service
- Radio-frequency interference in the vehicle environment
Symptoms
- TPMS warning lamp or dash message indicating low battery on sensor 3
- Intermittent or missing tire pressure readings for rear-left wheel
- Inability to complete TPMS sensor relearn procedure for that wheel
- Inconsistent/erratic pressure readings or repeated warnings for that wheel
What to check
- Read DTCs with an appropriate scan tool and record sensor ID and any related codes
- Confirm vehicle displays which wheel corresponds to sensor 3 (owner manual or OEM tool)
- Use a TPMS activation tool to attempt to wake sensor 3 and read its battery/telemetry data
- Visually inspect the rear-left sensor and valve stem for damage, corrosion, or loose hardware
- Check for recent wheel/tire service or replacement of sensors that could have changed IDs
- Inspect TPMS receiver/antenna wiring and ground connections for damage or corrosion if sensor cannot be detected
Signal parameters
- Typical TPMS transmit frequency depends on market: commonly 315 MHz or 433 MHz (vehicle-specific)
- TPMS sensors are battery-powered (nominal internal cell ≈ 3 V lithium); low-voltage fault is reported when voltage falls substantially below nominal
- Sensors transmit periodic broadcast and wake-on-motion or on-activation from a TPMS tool
- Data transmitted: sensor ID, tire pressure, temperature, and battery state indicator (if supported)
Diagnostic algorithm
- Connect a diagnostic scanner and confirm C1123 and any related TPMS codes; note sensor ID and position. 2) Verify the dashboard message and confirm vehicle maps sensor 3 to rear-left wheel. 3) Attempt to activate sensor 3 with a TPMS service tool at the wheel and read transmitted data (pressure, temp, battery indicator). 4) If the sensor responds but reports low battery, plan to replace the sensor (or replace battery if serviceable). 5) If the sensor does not respond, inspect the sensor and valve stem for mechanical damage; remove wheel/tire if needed to access the sensor. 6) Check TPMS receiver/antenna connections and communication lines at the ECU if multiple sensors fail or if the scanner shows receiver faults. 7) After replacing a sensor or repairing receiver, perform the required TPMS learn/relearn procedure per OEM instructions. 8) Clear codes and road-test to verify the new/ repaired sensor reports correctly and that the C1123 does not return. Note: when replacing sensors, use correct frequency/type and program or learn the new sensor per manufacturer procedure.
Likely causes
- Internal battery of rear-left (sensor 3) TPMS sensor is weak or near end of life
- Sensor physically damaged during tire change or by impact
- Receiver/antenna for TPMS has poor connection or partial failure
- Sensor ID not recognized after wheel swap or replacement
Fault status
Status
C1123 — Rear-left (sensor 3) TPMS sensor internal battery voltage is below the expected threshold. The sensor may report low battery, stop transmitting, or produce intermittent data until the sensor is replaced or the receiver/communication fault is fixed.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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