AU
C003800

DTC C003800 indicates the IPB (Intelligent Integrated Braking System) control unit detects the left rear wheel speed sensor supply voltage is outside the normal range (typically 12V or 5V, depending on the sensor model) — Atto 3

Braking System

DTC C003800 indicates the IPB (Intelligent Integrated Braking System) control unit detects the left rear wheel speed sensor supply voltage is outside the normal range (typically 12V or 5V, depending on the sensor model).

This fault indicates an open circuit, short to ground, short to power, or excessive contact resistance in the power supply circuit between the IPB module and the left rear wheel speed sensor.

This prevents the sensor from receiving a stable operating voltage.

Because the wheel speed signal is a core parameter for ABS, ESC, TCS, AEB, and vehicle speed calculations, this fault causes these functions to fail or enter a degraded mode.

On some hybrid models (such as DM-i), the abnormal vehicle speed signal may also restrict EV mode switching and permit only HEV mode driving for safety.

The C003800 fault code on the Atto 3 indicates the IPB braking control unit has detected abnormal supply voltage to the left rear wheel speed sensor. Severity is medium because ABS, ESC, TCS, AEB, and speed-related functions may be reduced or disabled. Common causes include damaged or shorted sensor wiring, corroded connectors, or loose terminals. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from 5 recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Short circuit or intermittent short circuit to ground in the left rear wheel speed sensor power supply circuit, pulling the voltage low (commonly due to wiring harness chafing through the insulation at suspension movement points).
  • 2Sensor connector oxidation, backed-out terminals, or loose connections increase contact resistance in the power supply circuit, causing an abnormal voltage drop.
  • 3Short circuit in the wheel speed sensor internal power supply circuit causes the IPB control unit to cut off the power supply for protection or results in abnormal voltage.
  • 4IPB control unit internal power management module fault, unable to output stable sensor supply voltage (relatively uncommon).
  • 5Water enters the sensor connector after vehicle wading or washing, decreasing the insulation resistance between the power supply terminal and the ground terminal.
What To Do
  • 1
    Use VDS or a dedicated diagnostic tool to read the complete fault codes and freeze frame data. Confirm if C003708 (signal fault) or a U-class communication fault is present. Check the data stream to verify if the left rear wheel speed value displays 0 km/h or jumps erratically.
  • 2
    Raise the vehicle and visually inspect the left rear wheel speed sensor connector for looseness, oxidation, or water ingress. Check the wiring harness securing points at the suspension control arm and body pass-throughs, and inspect for wear, cuts, or scorch marks.
  • 3
    Disconnect the sensor connector, turn the ignition to the ON position, and measure the voltage between the sensor-side power supply pin and ground. Normal voltage is 12V±0.5V or 5V±0.25V (refer to the specific vehicle repair manual). A voltage of 0V or below 9V indicates a power supply fault.
  • 4
    Disconnect the IPB control unit wiring harness connector. Measure the continuity of the power supply circuit between the IPB and the sensor (resistance must be less than 1Ω) and insulation (resistance to ground must be greater than 10MΩ). Closely inspect harness bends and the inside of the protective sleeve.
  • 5
    Measure the wheel speed sensor resistance (normal range: approx. 1.0-2.0 kΩ, depending on the model). If the resistance is too low (close to 0 Ω), this indicates an internal short circuit causing an abnormal power supply. Replace the sensor.
  • 6
    If the wiring and sensor are normal, measure the output voltage at the corresponding IPB control unit pin. If the voltage remains abnormal, this indicates an internal IPB fault. Replace the integrated brake assembly or repair the control unit.
  • 7
    After repairing or replacing the faulty wiring harness or sensor, reconnect the connector. Apply conductive paste and insulating sealant. Route and secure the wiring harness correctly, leaving sufficient slack. Clear the fault code and perform a road test to confirm the ABS/ESC warning light turns off and the wheel speed signal in the data stream matches the actual vehicle speed.
Real-World Cases
BYD DTC AI Analysis

Chafed left rear wheel speed sensor wiring harness caused short to power on Song PLUS DM-i

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When driving on rough roads, the ABS warning light illuminated intermittently. The scanner retrieved DTCs C003800 and C003708. Inspection found the left rear wheel speed sensor harness retaining clip detached where it passes the rear suspension lower control arm. The harness chafed against the arm, damaging the insulation and causing the power supply wire (red/black) to short intermittently to ground. This caused the IPB to detect supply voltage momentarily dropping below 2V. Repair: Wrapped the damaged section with waterproof tape, fitted abrasion-resistant corrugated tubing, and re-secured the harness routing. Cleared the fault codes and road-tested 20 kilometres; the fault did not return.
Original source ↗
BYD DTC AI Analysis

Qin Pro EV sensor connector water ingress and oxidation caused abnormal supply voltage

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After driving through water, the ABS light remained on with an ESC warning. Read DTC C003800 (left rear wheel speed sensor supply voltage fault). Found visible water inside the left rear wheel speed sensor connector; the supply terminal (pin 1) oxidised and blackened, increasing contact resistance to 15Ω (normal <0.5Ω). Sensor operating voltage dropped to 7.5V (below the 9V minimum). Cleaned the connector with electrical contact cleaner, polished the terminal with fine sandpaper to a metallic finish, applied conductive grease, and reassembled. Fault cleared.
Original source ↗
BYD DTC AI Analysis

e5 taxi wheel speed sensor internal short burned out IPB fuse

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Vehicle failed to power up or communicate with the IPB system. Left rear wheel speed sensor supply voltage read 0V. Inspection found the sensor internal power circuit shorted, blowing the IPB control unit protection circuit or triggering a software protective cutoff. Replaced the left rear wheel speed sensor (Part No.: BYD-3635100) and performed an IPB system reset and sensor calibration with a diagnostic tool. Supply voltage returned to 12V and fault codes cleared.
Original source ↗
BYD DTC AI Analysis

Misconnected wiring harness after accident repair causes Song Pro overvoltage

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After left rear accident repairs, the instrument cluster displayed a brake system fault with DTC C003800 stored. Inspection found the left rear wheel speed sensor power supply incorrectly connected to the reverse lamp feed (12V constant), locking the sensor voltage at 12V. The IPB normally supplies regulated 12V to this sensor, so the static voltage violated its monitoring logic. Technicians restored the harness connections per the wiring diagram and factory routing, clearing the fault.
Original source ↗
BYD DTC AI Analysis

Tang DM-i IPB control unit internal power supply module fault

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The vehicle repeatedly set a left rear wheel speed sensor supply voltage fault. External wiring continuity, insulation, and the connector all tested normal. Replaced the sensor; the fault persisted. Further diagnosis found the DC-DC module inside the IPB control unit (One Box) powering the left rear wheel speed sensor was outputting abnormal voltage, fluctuating between 4-14V. Since the IPB is an integrated brake unit, replaced the IPB assembly (part number: BYD-3530100A), programmed and matched the unit, and completely cleared the fault.
Original source ↗
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.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.
Common problems reported for Atto 3 →Atto 3 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.