AU
C055700

DTC C055700 indicates the IPB (Intelligent Integrated Braking System) detects the left rear wheel speed sensor electrical characteristics, signal pulse count, or communication protocol do not match system calibration parameters during self-check or signal monitoring — Seal U

Braking System

DTC C055700 indicates the IPB (Intelligent Integrated Braking System) detects the left rear wheel speed sensor electrical characteristics, signal pulse count, or communication protocol do not match system calibration parameters during self-check or signal monitoring.

This fault is not a simple signal loss or short circuit; rather, the system identifies an abnormal sensor "identity".

Possible causes include installing a non-genuine wheel speed sensor with incorrect specifications (mismatched resistance, pole count, or Hall element type), an abnormal match between the sensor and the tone ring (magnetic ring), or incorrect IPB control module software configuration (such as flashing configuration data from another vehicle model).

This fault directly limits or completely disables functions relying on accurate wheel speed signals, including ABS, ESC, and EPB.

In extreme cases, it causes wheel lock-up or skidding during emergency braking, making it a critical fault affecting driving safety.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Installed a non-genuine or incorrect wheel speed sensor (e.g., using a passive magnetic sensor from a conventional ICE vehicle instead of the BYD-specific Hall-effect sensor, or a sensor with a mismatched pole count).
  • 2The left rear wheel bearing unit (including the magnetic ring/tone ring) does not match the sensor. For example, installing a bearing with the incorrect specification causes an abnormal number of magnetic poles or abnormal air-gap magnetic field strength.
  • 3IPB control module software programming error: writing an incorrect vehicle model configuration code (e.g., writing Tang model wheel speed parameters to a Song model) causes the system to misidentify the sensor type.
  • 4Water ingress, oxidized pins, or abnormal contact resistance at the wheel speed sensor wiring harness connector alters the signal waveform characteristics, causing the system to incorrectly identify the sensor type.
  • 5Deformed sensor mounting bracket or out-of-tolerance installation gap (standard: 0.3-1.2 mm) causes abnormal output signal amplitude, triggering a model identification fault.
What To Do
  • 1
    Use the BYD VDS2000/3000 diagnostic tool to read all fault codes and freeze frame data. Confirm if C055700 is a current fault and check for accompanying related fault codes, such as C055600 (front right) and C055800 (rear right).
  • 2
    Check the Electronic Parts Catalog (EPC) to verify the left rear wheel speed sensor part number (typically a 3C-3630100 series Hall sensor for Song PLUS DM-i). Check the actual vehicle sensor part number, resistance (normally 1.0–1.5 kΩ), and pole count (typically 46 or 48 poles, depending on configuration).
  • 3
    Check the sensor installation condition: remove the left rear wheel speed sensor and check the tip for metal swarf contamination; measure the air gap between the sensor and the tone ring using a feeler gauge (must be 0.3-1.2 mm); check the tone ring for missing teeth or deformation.
  • 4
    Measure the sensor output signal using an oscilloscope: rotate the wheel and verify the waveform is a standard square wave, the frequency is proportional to vehicle speed, and the amplitude is within the normal range (high level ≥4.5V, low level ≤0.5V).
  • 5
    Check the IPB control module software version and configuration code: Access the IPB system special functions, read the vehicle model configuration information, and verify the configuration matches "Song PLUS DM-i". If incorrect, reflash the correct configuration or upgrade to the latest software version.
  • 6
    Replace with a genuine standard wheel speed sensor (verify the part number matches the factory original). Clean the sensor mounting hole, tighten to the specified torque (usually 8-10Nm), and apply an appropriate amount of grease to prevent seizing.
  • 7
    Perform the sensor calibration procedure (if applicable): On some models, select the "Wheel Speed Sensor Learning" or "ABS System Bleeding and Calibration" function on the diagnostic tool. Clear the fault code, perform a road test, and confirm all four wheel speed data streams synchronize and show no abnormal spikes.
Real-World Cases
BYD DTC AI Analysis

Aftermarket wheel speed sensor pole count mismatch caused C055700

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A 2021 BYD Song PLUS DM-i had its left rear wheel speed sensor replaced at a non-authorized repair shop following a left rear wheel accident. After driving approximately 500 km, the ABS and ESC warning lights illuminated on the instrument panel. Fault code C055700 was retrieved. Comparison showed the replacement sensor was a 48-pole unit, while the Song PLUS DM-i requires a 46-pole Hall sensor for the left rear wheel. Installing genuine part number 3C-3630100, performing IPB system calibration, and clearing the fault code restored normal wheel speed data for all four wheels.
BYD DTC AI Analysis

Software configuration error after IPB assembly replacement caused the fault.

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After the IPB pump body failed and was replaced with a new assembly, the technician failed to write the vehicle configuration before installation. This mismatch between the system default settings and the actual vehicle threw fault codes C055700 and C055600. Using a diagnostic tool, enter the IPB system "Vehicle Configuration" function, select the corresponding configuration code for "Song PLUS DM-i" (e.g., SA-XXX), and write the data. After the write succeeds, power down and let the system sleep for 5 minutes. The fault codes clear automatically. Dynamic testing confirms normal synchronization of all wheel speed signals.
BYD DTC AI Analysis

Rear wheel bearing replacement with incorrect magnetic ring specification

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LH rear wheel bearing noise. Replaced with an aftermarket bearing unit (with magnetic ring); DTC C055700 set. The replacement unit's built-in magnetic ring has 32 poles versus OEM 46, causing the IPB to flag the sensor output frequency as a model error. Replaced with OEM rear wheel bearing unit (with magnetic ring). Fault resolved. When replacing wheel hub bearings, confirm the magnetic ring pole count matches OEM.
BYD DTC AI Analysis

Water ingress into the sensor connector caused oxidation, resulting in abnormal signal characteristics.

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Water entered the left rear wheel speed sensor connector after driving through water, causing internal oxidation and increased signal line contact resistance. The distorted output signal waveform (slowed rising edge) caused the IPB to misdiagnose a sensor model error (C055700). Disassembling the connector revealed green corrosion on the pins. Cleaned the terminals, applied conductive grease, and confirmed normal resistance. Reinstalled the connector and cleared the fault code. Inspect chassis wiring harness waterproofing.
Other Seal U 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.