AU
C056B00

DTC C056B00 indicates an abnormal signal from the main pressure sensor (Pressure Sensor 1) inside the IPB (Intelligent Power Brake) module — Seal U

Braking System

DTC C056B00 indicates an abnormal signal from the main pressure sensor (Pressure Sensor 1) inside the IPB (Intelligent Power Brake) module.

This sensor typically monitors hydraulic pressure in the brake master cylinder or booster chamber, providing critical input for the ABS, ESC, regenerative braking system (RBS), and electric brake assist functions.

The IPB ECU sets this fault when the sensor output voltage falls outside the calibrated range (typically 0.5-4.5V), the signal drift rate is abnormal, or the cross-check difference with a redundant sensor (such as Pressure Sensor 2) exceeds the threshold (e.g., a pressure value corresponding to ±0.3V).

When this fault occurs, the vehicle may enter brake assist degraded mode (hard brake pedal), limit ESC/ABS functions, disable automatic emergency braking (AEB), and illuminate multiple brake system warning lamps on the instrument cluster.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Damaged or aged internal pressure sensor element in the IPB integrated electro-hydraulic module, causing unstable or inaccurate signal output.
  • 2Loose sensor wiring harness connector, backed-out pins, water ingress and oxidation, or pin corrosion, causing signal transmission interruption or crosstalk.
  • 3Brake fluid contamination (excessive water content or impurities) blocks the sensor port or causes internal corrosion.
  • 4IPB module power supply system fault (battery voltage below 9V or above 16V, or poor grounding) causing sensor reference voltage drift.
  • 5Trapped air or a micro-leak in the brake system causes delayed pressure build-up or abnormal pressure retention, triggering a sensor logic plausibility check failure.
What To Do
  • 1
    Use the BYD VDS2000 dedicated diagnostic tool or Launch X431 to read the complete fault codes. Confirm whether C056B00 is a Current or History fault. Record the freeze frame data (key parameters when the fault occurred, such as vehicle speed, pedal travel, pressure values, and system voltage).
  • 2
    Perform a preliminary visual inspection: verify the brake fluid level is between MIN and MAX, the brake fluid is clear (not black or milky), the IPB module has no leaks or impact deformation, and the wiring harness connector is fully locked.
  • 3
    Disconnect the low-voltage wiring harness connector from the IPB module. Use a multimeter to check the voltage and continuity of the pressure sensor power supply pin (usually 5V reference voltage), signal feedback pin, and ground pin. Check the pins for push-out, enlarged terminals, green oxidation, or burn marks.
  • 4
    Connect the diagnostic tool and enter Live Data mode. Monitor the real-time value of Pressure Sensor 1: at rest, it should be close to 0 bar; when applying the brake pedal, it should rise linearly with pedal force (up to 150-200 bar). Compare the value with Pressure Sensor 2 (if equipped). The difference between the two must be less than 5 bar; otherwise, the sensor is faulty.
  • 5
    Perform the brake system bleeding procedure (use the diagnostic tool to trigger the IPB into bleeding mode), purge air from the brake lines, and observe if the fault code becomes intermittent or clears.
  • 6
    If the wiring harness and hydraulic system are normal, flash the IPB control unit software to the latest version (some early 2021-2022 software versions have a defect in the sensor signal filtering algorithm).
  • 7
    If the above steps fail, replace the IPB integrated electro-hydraulic brake booster assembly. After replacement, perform: a) Brake system bleeding; b) Pressure sensor calibration (Sensor Calibration); c) ESC system initialization; d) Road test to verify braking performance.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i: Brake pedal stiffened and multiple warning lights illuminated

✓
A 2021 Song PLUS DM-i with 32,000 km came in after the owner reported the dashboard suddenly displaying "Braking System Fault" and "ESC Fault" while driving, with the brake pedal feeling noticeably hard. DTC C056B00 (current fault) present. The IPB module showed no external damage and wiring harness connectors locked properly. Live data revealed Pressure Sensor 1 stuck at 0.2V without changing, while Sensor 2 varied normally with pedal input. Disconnecting the connector showed infinite resistance between the Sensor 1 signal line and ground; the 5V supply read normal. Diagnosed as internal failure of Pressure Sensor 1 in the IPB. Replaced the IPB assembly, bled the brakes, and performed calibration. Fault resolved.
BYD DTC AI Analysis

BYD Seal: Brake warning light comes on intermittently after driving through water

✓
2022 BYD Seal developed intermittent ABS and ESC warning lights after wading through heavy rain, with fault code C056B00 appearing intermittently. Inspected the IPB module (left front engine bay) and found moisture in the wiring harness connector; pin A03 (pressure sensor signal) showed slight green oxidation. Cleaned the connector with electronic cleaner, dried it, applied conductive grease, and reconnected. No recurrence after one week of monitoring. Water entered the connector during wading, causing intermittent signal open circuit.
BYD DTC AI Analysis

BYD Qin PLUS DM-i set pressure sensor fault after brake fluid replacement

✓
A Qin PLUS DM-i showed a brake system fault on the instrument cluster after a non-authorised workshop replaced the brake fluid. We retrieved fault code C056B00. Inspection revealed the workshop had used substandard brake fluid that did not meet DOT4 specifications and had failed to bleed the system properly. Impurities in the brake fluid blocked the sensing port of IPB internal pressure sensor 1, causing signal anomalies. We flushed the brake system and replaced the fluid with genuine Changyue DOT4. We performed the IPB bleeding procedure using a diagnostic tool (cycling the motor and solenoid valves), followed by multiple bleeding cycles. The sensor signal returned to normal; we cleared the fault code to resolve the issue.
BYD DTC AI Analysis

BYD Yuan Plus brake power assist failure on cold start

✓
An Atto 3 displayed "Brake Booster System Fault" on the dashboard after a cold start at -10°C. Fault code C056B00 appeared only when cold and cleared after warm-up. Data stream readings revealed severe zero drift in pressure sensor 1 at low temperatures (showing -5 bar; normal 0±0.5 bar). IPB supply voltage dropped to 8.2V during startup, indicating battery degradation (increased internal resistance). The cold-crank voltage sag caused unstable sensor reference voltage. Replacing the battery and inspecting the charging system resolved the fault.
BYD DTC AI Analysis

Han EV false pressure sensor fault after software update

✓
A 2020 Han EV triggered DTC C056B00 the day after a multimedia system upgrade at the 4S dealership (non-brake system). Technicians inspected the IPB hardware and wiring harness and found no faults. Data stream readings showed pressure sensor 1 fluctuating between 0.1-0.3V while stationary. They reflashed the IPB control unit from V1.2 to V2.1. After the flash, sensor signal filtering normalized and the fault code did not return. The original software generated false positives under specific voltage fluctuations; the V2.1 algorithm optimization resolved this.
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.