AU
C057900

DTC C057900 indicates the IPB (Integrated Power Brake) electro-hydraulic control module detected a short to ground in the brake booster motor temperature sensor signal circuit — Seal U

Braking System

DTC C057900 indicates the IPB (Integrated Power Brake) electro-hydraulic control module detected a short to ground in the brake booster motor temperature sensor signal circuit.

Typically integrated inside the electro-hydraulic brake booster, this temperature sensor uses a negative temperature coefficient (NTC) thermistor to monitor the booster motor operating temperature in real time and prevent overheating damage.

The ECU logs a short to ground fault when the sensor signal voltage remains below the calibrated threshold (typically <0.5V) for longer than the set time (e.g., 200ms).

This fault triggers the IPB system to enter a degraded safety mode, which may reduce or eliminate brake assist (hard brake pedal), disable the energy recovery system, restrict ABS/ESC functions, and illuminate multiple brake system warning lights.

Continued driving under extreme operating conditions may cause a complete loss of brake assist, posing a serious safety risk.

Workshop practice on certain vehicle models indicates this DTC may also involve a short to ground in the brake switch signal circuit.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Brake booster temperature sensor internal thermistor breakdown or short circuit, or damaged wiring harness insulation.
  • 2Signal wiring harness between the IPB electro-hydraulic module and the sensor (usually located near the engine compartment firewall) shorted to body ground due to vibration chafing or cuts from sharp edges.
  • 3Poor sealing of the IPB electro-hydraulic module connector (usually located near the brake master cylinder) causes water ingress, corrosion, or bent pins, short-circuiting the temperature signal pin (such as pin TBD) to the ground pin.
  • 4IPB control unit internal signal sampling circuit fault, such as a burnt current-limiting resistor or ADC input port short to ground.
  • 5Improper wiring harness routing during repair or missing retaining clips causes the harness to chafe against a metal bracket over time, resulting in an intermittent short to ground.
What To Do
  • 1
    Use the VDS2000/3000 diagnostic tool to read fault codes. Confirm C057900 is a current fault (Active). Record the ambient temperature and sensor voltage values from the freeze frame data.
  • 2
    Visually inspect the IPB electro-hydraulic module and 24-pin (or corresponding model) connector for obvious signs of water ingress, burn marks, pin corrosion, or mechanical damage.
  • 3
    Disconnect the IPB connector. Use a multimeter to measure the resistance between the temperature sensor signal pin (refer to the circuit diagram; usually the specific temperature sensor input pin) and body ground. If the resistance is <5Ω, this confirms a circuit short to ground. Also measure the resistance of the sensor itself (normal range is typically 2-10kΩ@25°C, decreasing as temperature rises).
  • 4
    Thoroughly inspect the wiring harness along its route from the brake booster to the IPB module. Specifically check the harness sleeve integrity in wear-prone areas near the firewall, steering column, and battery bracket. If necessary, use a probe to check the wire insulation.
  • 5
    If the wiring harness inspection shows no faults, replace the brake booster assembly with integrated temperature sensor (the sensor is typically not available separately) or replace the entire IPB electro-hydraulic module assembly (to rule out an internal circuit fault).
  • 6
    After repairing or replacing the faulty component, clear the fault code and perform the IPB system calibration procedure (including brake pedal position learning, pressure sensor zero-point calibration, and motor travel learning).
  • 7
    Perform a static test and road test to confirm the fault code does not return. Verify normal brake assist function and regenerative braking system operation. Use a diagnostic tool to read the temperature sensor data stream and verify it displays normal temperature values.
Real-World Cases
BYD DTC AI Analysis

BYD Qin Pro DM brake switch internal contacts oxidised

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Symptoms: Vehicle failed to enter READY state (no HV activation). Cluster showed "Check Brake System" and "Check ESP System". Brake lights stayed off when pressing the pedal. Scanner read code C057900 (brake switch signal abnormal). Vehicle started occasionally, but cruise control did not work. Diagnostic process: 1. Connected VDS2000/3000 and checked codes. Only C057900 present; no related faults. 2. Consulted the wiring diagram. Brake switch uses four wires (dual signal): pin 1 constant power (B+), pin 2 ground, pin 3 signal 1 (normally open), pin 4 signal 2 (normally closed). 3. Disconnected the brake switch connector. Pin 1 measured 12V; pin 2 grounded normally. Reconnected the connector and checked signal pins. When pressing and releasing the brake pedal, pin 3 stayed at 0V (no change) and pin 4 stayed at 12V (no change). 4. Removed the brake switch. Internal contacts were severely oxidised and burnt, preventing the signals from conducting. Solution: Replaced brake light switch assembly (part number: 3720A-XXXXX, verify for your model year). Cleared codes and test drove. Vehicle now enters READY normally, brake lights work with the pedal, fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song PLUS brake switch installation clearance improper

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Symptoms: ESP warning light illuminates intermittently while driving, accompanied by flashing oil pressure warning light (false alarm). Fault code: C057900. Owner reports: (1) AUTO HOLD function fails intermittently; (2) When releasing the brake to pull away, vehicle occasionally surges (sudden power delivery); (3) Cruise control cannot be set. Diagnosis: Connected scan tool to monitor live data. Brake pedal status signal fluctuated rapidly between "depressed" and "released" without driver input. Physical inspection revealed approximately 2 mm clearance between brake switch and pedal plunger (specification: 0–1 mm). Because the switch was not fully compressed, road vibration caused poor contact, creating an intermittent signal the ECU flagged as abnormal. Repair: Loosened brake switch locknut, threaded switch body two turns toward pedal to close gap, confirmed plunger fully depressed at pedal rest position (faint click audible), then tightened locknut. Cleared fault codes and completed 50 km test drive; fault did not return.
Original source ↗
BYD DTC AI Analysis

BYD Yuan EV535 brake switch wiring harness connector pin backed out

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Vehicle starts, but the instrument cluster continuously displays "Check Brake System" with DTC C057900. Notable symptoms: When depressing the brake pedal, the high-mount stop lamp lights up, but the side brake lamps do not (or vice versa), and the vehicle intermittently cannot shift out of Park. Diagnosis: 1. Checked the brake switch fuse (F2/23 10A) — normal. 2. Disconnected the brake switch harness connector (located at the upper brake pedal, black 4-pin plug). Found pin 3 (signal wire) backed out approximately 3mm, not making effective contact with the switch terminal. 3. Found the pin retention latch broken, causing poor contact. Further inspection revealed a wiring harness manufacturing defect in this model batch; the pin was not properly crimped. Repair: Extracted pin 3 using a terminal release tool, re-crimped the terminal, and secured the harness to the body with cable ties to eliminate strain. Applied conductive paste to the connector and wrapped it with waterproof tape to prevent recurrence. Installed an improved brake switch (with harness assembly). Fault completely resolved.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM brake switch signals not synchronized

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Symptoms: Starts normally when cold. After about 10 minutes of driving, the dash shows "Braking System Fault" with DTC C057900. Also: the EPB won't auto-release (must release manually), and regen drops out suddenly during deceleration. Diagnostic Process: 1. Checked brake switch dual signals (primary and redundant) in live data. When cold, the two signals showed opposite logic (normal: one at 0V, one at 12V; abnormal: both at 12V or both at 0V). 2. Fault appeared after warm-up. Determined the brake switch has poor internal thermal stability; both contact sets stick simultaneously when hot. 3. Switch power and ground checked normal. Ruled out wiring. Confirmed internal switch fault. Solution: Replaced the OEM brake light switch (Tang DM requires the four-wire dual-signal type—do not use a standard two-wire switch). After replacement, ran "Brake System Calibration" with a scan tool (some models require this) to learn the pedal free-travel position. After calibration, both signals resumed opposite logic and the DTC cleared.
Original source ↗
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.