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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.

5
Cases Logged
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.
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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.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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.