AU
C000B04

The BYD new energy vehicle fault code system defines C000B04 as Left Rear Wheel Speed Sensor Circuit Low Input — Seal U

Braking System

The BYD new energy vehicle fault code system defines C000B04 as Left Rear Wheel Speed Sensor Circuit Low Input.

The IPB (Intelligent Integrated Braking System) or ESC module triggers this code when the left rear wheel speed sensor signal voltage remains continuously below the threshold (typically <0.5V), or when the sensor circuit experiences a short to ground or an open circuit.

This fault limits or disables the ABS, ESC, TCS, and Automatic Emergency Braking (AEB) functions, and illuminates the ABS/ESC warning light on the instrument cluster.

Some sources incorrectly label this code as "ACC communication timeout" (the C000Axx series typically covers actual ACC communication faults).

However, based on BYD’s standard fault code structure ('B' represents Left Rear and '04' represents circuit low input), this code fundamentally identifies a chassis wheel speed signal fault that severely compromises vehicle dynamic stability and braking safety.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Internal short or open circuit in the left rear wheel speed sensor (damaged sensor coil insulation causing abnormal resistance)
  • 2Sensor wiring harness short to ground, open circuit, or connector oxidation/water ingress (common due to poor sealing after water exposure in the left rear wheel area).
  • 3Wheel hub bearing magnetic encoder ring (magnetic toothed ring) damaged, cracked, contaminated with iron filings, or demagnetized
  • 4Abnormal sensor installation gap (normal gap 0.3-1.2mm). Excessive gap causes a weak signal; insufficient gap causes friction damage.
  • 5Internal fault in the IPB/ESC control unit wheel speed signal processing circuit (damaged signal amplifier, relatively rare)
What To Do
  • 1
    Use the VDS2000/VDS1000 diagnostic tool to read the DTC freeze frame data, confirm the vehicle speed, wheel speed values, and system status at the time of the fault, and check for other wheel speed sensor fault codes.
  • 2
    Raise the vehicle and visually inspect the left rear wheel speed sensor. Check the connector for looseness, water ingress, or oxidation (focus on damaged sections of the wiring harness corrugated conduit). Inspect the wiring harness for wear or damage.
  • 3
    Disconnect the sensor connector and measure the sensor resistance (normal range: 1.0-1.5kΩ at 20°C). Measure the insulation resistance to ground on the wiring harness side (should be >10MΩ) and check for a short to ground.
  • 4
    Inspect the condition of the wheel hub bearing magnetic encoder ring. Check for cracks, chips, adhered iron filings, or demagnetization. Clean the encoder ring surface. Replace the wheel hub bearing assembly if necessary.
  • 5
    Measure the sensor installation gap (using a feeler gauge or checking the mounting hole for wear). Verify the gap is 0.3-1.2mm. Inspect the sensor tip for metal debris.
  • 6
    Check wiring harness continuity from the IPB to the sensor, focusing on the transition connector between the body and suspension wiring harnesses. Measure the CAN line and power supply voltages.
  • 7
    Replace the left rear wheel speed sensor (prefer genuine parts) and road test the vehicle. Drive 5-10 km to perform dynamic learning. If the fault persists, replace the wheel hub bearing assembly. Finally, consider replacing the IPB assembly.
Real-World Cases
BYD DTC AI Analysis

Song Pro DM right front wheel speed sensor open circuit fault

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Vehicle: 2019 BYD Song Pro DM. Symptoms: ABS and ESC warning lights suddenly lit up while driving, traction control disabled, and speedometer display abnormal. Diagnosis: The 4S shop scanned with VDS and found no signal from the right front wheel speed sensor. The sensor resistance measured infinite, indicating an internal coil open circuit. Fix: Replaced the right front wheel speed sensor, cleared the fault codes, and performed wheel speed sensor calibration. Fault resolved. Cost: approximately ¥280 (including labor).
Original source ↗
BYD DTC AI Analysis

Qin Pro EV left rear wheel speed sensor intermittent fault

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Vehicle: 2018 BYD Qin Pro EV. Symptoms: ABS light comes on after rain or washing, clears after driving for a while. DTC C0037 (left rear wheel speed sensor intermittent fault). Diagnosis: Water ingress and oxidation in the left rear wheel speed sensor connector caused intermittent signal interruption; resistance readings were erratic. Solution: Cleaned the sensor connector contacts with electronic cleaner, applied conductive grease to prevent corrosion, rewrapped and sealed with waterproof tape and heat shrink tubing. No parts replaced.
Original source ↗
BYD DTC AI Analysis

Song Plus DM-i left rear wheel speed sensor water ingress damage

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Vehicle: BYD Song PLUS DM-i 2021 (same C000B04 applicability). Symptoms: After wading through water, the dashboard displayed 'Braking System Fault' and the ABS and automatic emergency braking warning lights stayed on. DTC C000B04 retrieved. Diagnosis: Found water in the left rear wheel speed sensor connector. Sensor resistance measured 0.2kΩ (far below the normal 1.0–1.5kΩ), indicating an internal short. Resolution: Replaced the left rear wheel speed sensor and resealed the wiring harness. Fault cleared. Advised the owner to check the left rear wheel arch liner sealing.
BYD DTC AI Analysis

Han EV wheel speed sensor signal interference fault

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Vehicle: BYD Han EV. Symptoms: ESC light flickering intermittently at high speed. DTC indicates left rear wheel speed sensor signal fault; sensor tested normal under static conditions. Diagnosis: Checked wheel speed signal waveform with an oscilloscope and detected high-frequency interference. Inspection found the sensor wiring harness running parallel to the high-voltage harness, generating electromagnetic interference. Fix: Re-routed the wiring harness to move the sensor wiring away from the high-voltage harness and added shield grounding. Fault resolved.
BYD DTC AI Analysis

Tang DM hub bearing magnetic encoder ring damaged

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Vehicle: 2020 BYD Tang DM. Symptom: ABS warning light stays on, DTC C000B04 stored, left rear wheel speed reading shows 0. Diagnosis: Replaced the wheel speed sensor but the fault persisted. Disassembly revealed severe scratches and partial demagnetisation on the hub bearing magnetic encoder ring—likely tool damage from previous brake work. Solution: Replaced the left rear hub bearing assembly (including magnetic encoder ring). Fault resolved.
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.