AU
C1205

DTC C1205 indicates the ABS/ESC control module continuously detects 0 V (no signal state) from the right front wheel speed sensor — Seal U

Braking System

DTC C1205 indicates the ABS/ESC control module continuously detects 0 V (no signal state) from the right front wheel speed sensor.

In BYD new energy vehicles, the control module logs an open circuit or sensor failure because the variable reluctance or Hall-effect sensor fails to transmit a valid sine or square wave signal to the ECU.

This fault forces the Anti-lock Braking System (ABS), Electronic Stability Control (ESC), Automatic Emergency Braking (AEB), Auto Vehicle Hold (AVH), and energy recovery systems into a degraded or failed mode, and illuminates the ABS/ESC warning lamps on the instrument cluster.

Unlike DTC C1204 (excessive signal variation/intermittent fault), C1205 represents a continuous signal loss, typically indicating a hard circuit fault or a damaged sensor.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Right front wheel speed sensor internal coil open circuit, burned-out Hall element, or internal circuit fault (resistance infinite or 0Ω)
  • 2Sensor wiring harness chafed or broken in high-vibration chassis areas, such as near the suspension control arm, or oxidized connector terminals, terminal back-out, or water ingress corrosion causing poor contact.
  • 3Wheel hub bearing wear or looseness causes the gap between the sensor and the tone ring (magnetic ring) to exceed specification (normal: 0.3-1.2 mm), or a loose sensor mounting bolt displaces the sensor.
  • 4The tone ring is damaged, missing teeth, severely deformed, or has a large amount of ferromagnetic metal debris adhered to its surface, shielding the magnetic circuit.
  • 5ABS control module internal signal processing circuit fault (signal input port shorted to ground or damaged sampling resistor; low probability)
What To Do
  • 1
    Connect the VDS diagnostic tool and read the DTC freeze frame. Confirm the right front wheel speed data stream remains at 0 km/h and the DTC cannot be cleared to rule out intermittent interference.
  • 2
    Raise the vehicle and visually inspect the right front sensor, wiring harness sleeve, and connector for damage, water ingress, oil contamination, or signs of physical impact.
  • 3
    Disconnect the sensor connector and use a multimeter to measure the sensor resistance (magnetic induction standard value: approx. 1.0-1.5kΩ@25℃; Hall effect requires a powered test). Replace the sensor if the resistance is abnormal.
  • 4
    Check the sensor tightening torque (standard: 8-10 N·m). Use a feeler gauge to measure the clearance between the sensor tip and the tone ring tooth crest (0.3-1.2 mm). Check the tone ring for missing teeth, cracks, or attached foreign matter.
  • 5
    Measure wiring harness continuity: From the sensor connector to the ABS pump connector, measure the resistance of the power (B+, 12V), signal (SIG), and ground (GND) circuits (must be <1Ω) and the insulation to ground and power (must be >10MΩ).
  • 6
    Perform a substitution test: Swap the right front and left front sensors. Conduct a road test and check if the fault code transfers to the left front to confirm a faulty sensor.
  • 7
    Check the ABS pump connector terminals for oxidation or backed-out pins, and measure the internal resistance of the corresponding ABS pump pins. If the circuit is normal but there is no signal input, the ABS control module is faulty. Replace the ABS assembly and complete the yaw rate sensor calibration.
Real-World Cases
BYD DTC AI Analysis

BYD E2 right front wheel speed sensor wiring harness worn through, open circuit

✓
A 2019 BYD E2 with 60,000 km showed ABS/ESC warning lights. Retrieved DTC C1205. Inspection found the right front sensor connector-to-body harness near the steering knuckle had boot damage from long-term steering friction, and the copper core wire was completely severed. Cut out the damaged harness section, re-soldered the wiring using waterproof heat-shrink tubing, and secured the harness routing to prevent suspension interference. Fault cleared.
BYD DTC AI Analysis

Yuan EV wheel hub bearing wear caused excessive sensor gap.

✓
2020 BYD Yuan EV presented with DTC C1205. Live data showed right front wheel speed stuck at zero. Sensor resistance measured normal and wiring continuity tested good, but the sensor-to-reluctor ring air gap measured 3.5 mm—severely out of specification. Further inspection found the right front wheel hub bearing worn and loose, allowing the reluctor ring to drop. Replaced the wheel hub bearing assembly (including the reluctor ring), restoring the air gap to 0.8 mm. Cleared the fault code; ABS function returned to normal.
BYD DTC AI Analysis

E1 sensor connector corroded by water ingress

✓
BYD E1 developed a C1205 fault after fording water. Removed the right front wheel speed sensor connector and found the internal terminals severely oxidised and white with electrolytic corrosion. The connector seal ring had aged and failed, letting water in during the crossing and shorting the signal terminal to ground. Cleaned the connector with precision electronic cleaner, replaced the seal ring and terminals, applied conductive grease. Fault resolved.
BYD DTC AI Analysis

E3 wheel speed sensor internal open circuit

✓
A 2020 E3 logged C1205 after accident repairs to the right front wheel. Sensor resistance measured infinite, indicating an open circuit in the internal coil. Replaced the sensor with a genuine part; fault remained. Further inspection found the accident had deformed the sensor mounting hole, causing the new sensor to twist under stress and fracture internally. Replaced the steering knuckle, reinstalled the sensor, and completely resolved the fault.
BYD DTC AI Analysis

Song EV reluctor ring accumulated metal debris causing signal shielding

✓
Following brake system repairs on a 2019 Song EV, the vehicle set DTC C1205. Checked the right front sensor and wiring—both were normal. Found the tone ring surface coated with ferromagnetic powder from brake pad wear, creating a magnetic shield that prevented the sensor from detecting the ring's magnetic field changes. Cleaned the metal debris from the tone ring surface and thoroughly cleaned it with carburetor cleaner. Signal returned to normal; cleared the fault code.
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.