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) — Seal U

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 Seal U indicates a supply voltage problem for the left rear wheel speed sensor, detected by the IPB braking control unit. Severity is medium because ABS, ESC, traction control, AEB, and speed calculations may be reduced or disabled. Common causes include damaged or shorted wiring and poor sensor connector contact from corrosion or loose terminals. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Short circuit or intermittent short to ground in the left rear wheel speed sensor power supply circuit, pulling the voltage low (commonly due to wiring harness insulation chafing at suspension movement points).
  • 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 protectively cut off power or results in abnormal voltage.
  • 4IPB control unit internal power management module fault, unable to output a stable sensor supply voltage (relatively uncommon).
  • 5Water ingress into the sensor connector after driving through water or washing the vehicle reduces the 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. View the data stream to check if the left rear wheel speed value displays 0km/h or jumps 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 mounting 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 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 1 Ω) and the insulation resistance (resistance to ground must be greater than 10 MΩ). Carefully inspect the wiring harness bends and inside 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 short circuit in the sensor 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 sealant. Route and secure the wiring harness to specification, 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

✓
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 Seal U Fault Codes
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.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.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.