AU
C003B00

This DTC indicates the IPB (Intelligent Integrated Brake System) controller detects the right rear wheel speed sensor (WSS) supply voltage falls outside the normal threshold range (typically 4 — Seal U

Braking System

This DTC indicates the IPB (Intelligent Integrated Brake System) controller detects the right rear wheel speed sensor (WSS) supply voltage falls outside the normal threshold range (typically 4.5V-16V, depending on vehicle configuration).

This is a hardwire circuit fault at the power supply level, not a signal transmission issue.

The IPB triggers C003B00 upon detecting a short to ground (voltage too low/0V), a short to power (voltage too high/battery voltage), or high circuit resistance (unstable voltage) at the right rear wheel speed sensor power terminal.

Because the wheel speed sensor provides a key input signal for the ABS, ESP, Automatic Emergency Braking (AEB), and Auto Hold systems, this fault causes a missing or distorted right rear wheel speed signal and triggers the brake system degraded mode.

Some models also limit maximum vehicle speed or disable regenerative braking.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Right rear wheel speed sensor power supply circuit short to earth: Chassis wiring harness chafes through the insulation at the cabin pass-through grommet, suspension moving parts, or floor wiring channel, causing the 12V/5V supply wire to short to earth.
  • 2Poor connector contact or corrosion: Water ingress, washing, or oxidation causes terminal back-out, intermittent connection, or excessive resistance at the right rear wheel speed sensor connector (near the rear knuckle) or the IPB module connector (engine compartment).
  • 3Internal short circuit in the wheel speed sensor power supply circuit: Breakdown of the internal voltage regulation circuit within the sensor body creates a short to ground, pulling down the supply voltage.
  • 4IPB controller internal power module fault: Damage to the IPB internal voltage regulator chip or MOSFET powering the wheel speed sensor causes abnormal output voltage on a specific channel.
  • 5Power supply interference caused by improper modifications: incorrectly drawing power from the wheel speed sensor supply circuit or damaging the wiring harness insulation during unauthorized installation of reversing sensors, dash cams, or modified audio systems.
What To Do
  • 1
    Diagnostic tool verification: Use VDS or a dedicated BYD diagnostic tool to read the DTC freeze frame. Verify the vehicle speed, supply voltage, and ambient temperature at the time of the fault to rule out intermittent false faults.
  • 2
    Visual inspection: Check the right rear wheel speed sensor connector (near the rear brake caliper) and the IPB module connector (left side of the front compartment or at the firewall) for signs of water ingress, terminal oxidation, looseness, or wiring harness damage. Closely inspect the chassis wiring harness for wear at the bulkhead rubber grommet.
  • 3
    Voltage measurement: Disconnect the right rear wheel speed sensor connector. Turn the ignition to ON. Measure the voltage between the power supply pin (usually pin 1 or 2; refer to the wiring diagram) and ground. The normal value is battery voltage (12V±0.5V) or reference voltage (5V±0.25V). If the voltage is abnormal, continue troubleshooting.
  • 4
    Wiring insulation and continuity test: Use a multimeter to measure the power supply circuit resistance to ground (>10 MΩ to rule out a short to ground) and circuit resistance (<1 Ω to rule out high resistance). Simultaneously measure for a short to power (must read no battery voltage).
  • 5
    Swap verification: Swap the right rear and left rear wheel speed sensors. Clear the fault code and road test the vehicle (including straight-line driving and turning). If the fault code transfers to C003900 (left rear), the sensor is faulty. If the fault remains C003B00, the fault is in the wiring harness or IPB.
  • 6
    Check the wiring harness in sections: If the fault does not transfer with the sensor, disconnect the IPB connector and measure the output voltage at the power supply pin from the IPB side. If the voltage is abnormal, the IPB is faulty. If the IPB output is normal, check the chassis wiring harness in sections, focusing on the floor wiring harness under the rear seat and the wiring harness near the rear suspension.
  • 7
    Repair and Verification: After repairing the wiring harness (re-wrap or replace the wiring harness assembly) or replacing the faulty sensor/IPB, clear the fault code. Perform a dynamic calibration of the wheel speed signal (some models require a diagnostic tool to execute 'wheel speed sensor deviation learning'). Finally, conduct a road test to verify normal ABS and ESP functions.
Real-World Cases
BYD DTC AI Analysis

Chassis wiring harness wear on Song PLUS DM-i caused power-to-ground short

✓
After driving through water, the ABS warning light illuminated with DTC C003B00. Inspection found the right rear wheel speed sensor connector dry, but tracing the harness forward revealed damage to the chassis harness grommet at the left rear seat bulkhead pass-through. The internal power wire insulation had worn through, exposing the copper and shorting to ground. Repair: Rewrapped the harness and adjusted the bulkhead grommet position to prevent interference. Fault resolved.
BYD DTC AI Analysis

Corroded sensor connector caused insufficient supply voltage

✓
The ESP warning light came on intermittently while driving. The scan tool showed C003B00 as a historical fault. Supply voltage measured only 3.2V during the fault (normal 12V). Inspection found white oxidation on the internal pins of the right rear wheel speed sensor connector, causing excessive contact resistance (2.3Ω). Cleaned the connector and applied conductive grease. Voltage returned to normal and the fault disappeared.
BYD DTC AI Analysis

Internal short in wheel speed sensor pulled supply voltage low

✓
Vehicle would not enter Ready mode and the ABS light stayed on. Measured the right rear wheel speed sensor supply voltage at 0V; voltage returned to 12V after disconnecting the sensor connector. Determined to be an internal power circuit short to ground within the sensor. Replaced the right rear wheel speed sensor and supply voltage returned to normal. Cleared fault codes and system function restored.
BYD DTC AI Analysis

IPB controller internal power module damaged

✓
After front-end collision repairs, multiple brake system warning lights lit up on the instrument panel. Diagnostics showed the right rear wheel speed sensor supply voltage at 16.5V (overvoltage). External harness inspection found no short circuits; the sensor tested normal. The IPB's internal voltage regulator circuit powering the wheel speed sensors had failed, causing excessive output voltage. Replaced the IPB assembly and performed brake bleeding and recalibration. Fault resolved.
BYD DTC AI Analysis

Aftermarket reversing sensors miswired to power supply caused voltage interference

✓
Owner reported the ABS warning light illuminates intermittently while driving after installing third-party reversing sensors. Inspection found the add-on device was drawing power from the wrong location—the right rear wheel speed sensor supply line—causing sensor supply voltage to fluctuate between 10.5V and 13V. Removed the improper power connection and restored the original wiring harness insulation. 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.