AU
C1208

On BYD E Series and Yuan Series models, DTC C1208 indicates the left rear wheel speed sensor (RLWSS) signal voltage to the ABS/ESP control module is 0V — Seal U

Braking System

On BYD E Series and Yuan Series models, DTC C1208 indicates the left rear wheel speed sensor (RLWSS) signal voltage to the ABS/ESP control module is 0V.

The control module detects no wheel speed pulse signal for over 100ms, indicating an open circuit, a short to ground, or a failed sensor.

The wheel speed signal is a core input parameter for the Anti-lock Braking System (ABS), Electronic Brakeforce Distribution (EBD), Traction Control System (TCS), and Electronic Stability Control (ESC).

A missing signal forces these safety systems into fail-safe mode (limp mode), halts their operation, and illuminates multiple warning lights.

In generic OBD-II definitions for Bosch ABS systems, C1208 typically indicates "Inlet Valve Coil Rear Circuit Short To Battery".

However, some BYD battery electric vehicles redefine this code as a left rear wheel speed sensor signal fault.

Consult the vehicle-specific workshop manual during repair.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left rear wheel speed sensor internal coil open or damaged (abnormal resistance; normal: 1.0-1.5kΩ)
  • 2Sensor wiring harness wears, breaks, or shorts to ground in the suspension travel area, especially after driving on rough roads.
  • 3Aged sensor connector seal allows moisture intrusion, oxidizing the pins and causing poor contact or signal interruption.
  • 4Signal ring gear (target wheel) damaged, missing teeth, heavily contaminated (metal shavings attached), or excessive sensor gap (>1.5mm).
  • 5ABS control module internal signal processing circuit fault or abnormal power supply (blown fuse, poor ground connection)
What To Do
  • 1
    Connect the VDS or Launch diagnostic tool, read and confirm DTC C1208 and freeze frame data. Verify the left rear wheel speed consistently displays 0 km/h, and check for accompanying related fault codes such as C1209 (right rear).
  • 2
    Raise the vehicle. Visually inspect the left rear wheel speed sensor installation and wiring harness routing. Specifically check the harness sleeve near the shock absorber and body pass-through hole for wear and exposed wires.
  • 3
    Disconnect the sensor connector. Measure the voltage at the sensor power supply terminal (12V±0.5V with ignition ON) and the resistance at the ground terminal (less than 1Ω) to confirm normal power supply.
  • 4
    Measure the sensor body resistance. The standard value is 1.0-1.5 kΩ (at 20°C). If the resistance is infinite (open circuit) or close to 0 Ω (short circuit), replace the sensor. Set a multimeter to the AC voltage scale, rotate the wheel, and measure the signal output. The sensor should generate an AC voltage of 0.1-2 V.
  • 5
    Inspect the signal tone ring, remove any metal filings, and confirm there are no cracks or missing teeth. Use a feeler gauge to check the air gap between the sensor and the tone ring (standard: 0.3-1.2mm).
  • 6
    If the sensor and wiring harness are normal, check the ABS control module connector (32-pin or 24-pin) for backed-out pins or oxidation. If necessary, measure circuit continuity between the module and the sensor.
  • 7
    Replace the faulty component (replace the sensor first, repair the wiring harness second, and consider the ABS pump assembly last). Clear the fault code and perform a road test to verify the repair (test ABS operation by applying emergency braking at speeds above 40 km/h).
Real-World Cases
BYD DTC AI Analysis

Hyundai/Kia models: C1208 ABS solenoid valve fault (Bosch shared-platform system reference)

✓
Hyundai and Kia models with the Bosch ABS 8.0 system may log DTC C1208: "Rear Inlet Valve Coil Circuit Short To Battery". ABS and ESP warning lights illuminate simultaneously. The scan tool shows the rear inlet valve solenoid coil shorted to battery. Measured solenoid resistance inside the ABS pump assembly: 0.5Ω (specification 2-8Ω), confirming an internal short. Replaced the ABS hydraulic control unit (Hydro Unit) to resolve. The BYD E2 and E3 use the same Bosch ABS platform; the fault mechanism and diagnostic procedure are identical.
Original source ↗
BYD DTC AI Analysis

BYD S6 ABS Pump Solenoid Valve Fault Repair Case

✓
A BYD S6 with 80,000 km had the ABS warning light suddenly come on while driving, with the brake pedal pulsation lost. Scanned ABS valve body circuit codes (not C1208, but same valve body circuit type). Checked ABS pump power and ground—normal. Measured solenoid coil resistances; rear wheel inlet valve read 1.2Ω (normal 3–5Ω), indicating an internal valve body coil short. Replaced the ABS pump assembly (including control module) and bled the system. Warning light went out; ABS function normal.
Original source ↗
BYD DTC AI Analysis

BYD Qin/Yuan Wheel Speed Sensor Wiring Harness Wear and Open Circuit Case

✓
Based on the BYD Qin workshop manual and Yuan EV owner forum feedback, the most common root cause of left rear wheel speed sensor fault C1208 is wiring harness chafing. Symptoms: the ABS warning light illuminates after driving over rough surfaces, and the diagnostic scanner shows left rear wheel speed at 0. Testing confirmed normal sensor resistance (1.3kΩ), but raising the vehicle revealed a damaged wiring harness sheath beneath the left rear shock absorber. The signal wire chafed against the suspension metal bracket when the body moved, breaking the copper conductors. We repaired the wiring harness by soldering the break and applying waterproof insulation, then resecured the harness routing with additional cable ties to prevent contact with moving components. Fault cleared.
Original source ↗
BYD DTC AI Analysis

GM C1208 Short Circuit Technical Diagnostic Bulletin

✓
The technical bulletin indicates that DTC C1208 ('ABS Inlet Valve Coil Rear Circuit Short To Battery') requires checking the wiring harness insulation between the ABS control module and hydraulic valve body. Check continuity between the module terminals and battery positive with a multimeter; continuity confirms the short. Common short points are the harness retaining clips near the ABS pump in the engine bay, where vibration damages the insulation and causes contact with chassis ground or the power wire. Repair the insulation, re-wrap the harness, and adjust the mounting points. Replace the ABS control module if necessary.
Original source ↗
Other Seal U Fault Codes
B1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.