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 8

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 8 indicates the left rear wheel speed sensor is not receiving the correct supply voltage from the IPB braking control unit. Severity is medium, as ABS, stability control, traction control, AEB, and speed-related functions may be reduced or disabled. Common causes include damaged wiring, a short to ground, or a loose or corroded sensor connector. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Short circuit or intermittent short circuit to ground in the left rear wheel speed sensor power supply circuit, pulling the voltage low (commonly caused by worn wiring harness insulation at moving suspension parts).
  • 2Sensor connector oxidation, terminal back-out, or looseness increases 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 power for protection or results in abnormal voltage.
  • 4IPB control unit internal power management module fault preventing stable sensor supply voltage output (relatively uncommon).
  • 5Water ingress into the sensor connector after vehicle wading or washing decreases insulation resistance between the power supply and ground terminals.
What To Do
  • 1
    Use VDS or a dedicated diagnostic tool to read the complete fault codes and freeze frame data. Check for an accompanying C003708 (signal fault) or U-class communication fault. Monitor the data stream to verify if the left rear wheel speed value reads 0 km/h or fluctuates abnormally.
  • 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-through holes, and inspect for wear, cuts, or scorch marks.
  • 3
    Disconnect the sensor connector, turn the ignition to ON, 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 its insulation (resistance to ground must be greater than 10MΩ). Specifically inspect harness bends and the inside of the protective sleeve.
  • 5
    Measure wheel speed sensor resistance (normal range approx. 1.0-2.0 kΩ, depending on model). If 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 pin of the IPB control unit. 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/sensor, reconnect the connector. Apply conductive paste and insulating adhesive. Properly secure the wiring harness, leaving sufficient slack. Clear the fault code and perform a road test. Verify 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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.