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 — Qin Plus

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.

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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Left rear wheel speed sensor internal coil open or damaged (abnormal resistance; normal: 1.0-1.5kΩ)
  • 2Sensor wiring harness chafes, breaks, or shorts to ground in the suspension travel area, especially after driving over rough roads.
  • 3Aged sensor connector seal allows moisture intrusion, oxidizing the pins and causing poor contact or signal interruption.
  • 4Signal ring gear (tone 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)
What To Do
  • 1
    Connect the VDS or Launch diagnostic tool. Read and confirm DTC C1208 and freeze frame data. Check if the left rear wheel speed consistently displays 0 km/h, and check for accompanying 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 wiring 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 the power supply is normal.
  • 4
    Measure the sensor body resistance. Standard value: 1.0-1.5 kΩ (at 20°C). Replace the sensor if the resistance is infinite (open circuit) or close to 0 Ω (short circuit). Set a multimeter to the AC voltage setting, rotate the wheel, and measure the signal output. The output should be 0.1-2V AC.
  • 5
    Inspect the signal tone ring appearance, 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, then repair the wiring harness, and finally replace the ABS pump assembly). Clear the fault code and perform a road test to verify the repair (apply emergency braking at speeds above 40km/h to test ABS operation).
Real-World Cases
BYD DTC AI Analysis

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

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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

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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

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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

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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 Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus overview →
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.