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) — Qin Plus

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 Qin Plus indicates the IPB braking control unit has detected abnormal supply voltage to the left rear wheel speed sensor. This is a medium-severity issue because it can affect ABS, ESC, traction control, AEB, and speed readings. Common causes include damaged wiring near the suspension or a loose, corroded sensor connector. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Left rear wheel speed sensor power supply circuit short to ground or intermittent short to ground, pulling voltage low (commonly caused by chafed 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 circuit causes the IPB control unit to cut power for protection or results in abnormal voltage.
  • 4Internal fault in the IPB control unit power management module prevents stable sensor supply voltage output (relatively uncommon).
  • 5Water ingress into the sensor connector after vehicle wading or washing reduces 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 0km/h or fluctuates abnormally.
  • 2
    Raise the vehicle. 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 the harness 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 should be less than 1 Ω) and the insulation (resistance to ground should be greater than 10 MΩ). Inspect the harness bend points and the inside of the protective sleeve.
  • 5
    Measure the wheel speed sensor resistance (normal range: approx. 1.0-2.0 kΩ, depending on model). If the resistance is too low (close to 0 Ω), it indicates an internal sensor 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, diagnose an internal IPB fault and 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 adhesive. Route and secure the wiring harness to specifications, 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

✓
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 Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.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.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.