AU
C004900

DTC C004900 indicates an abnormal brake fluid level detected by the IPB (Intelligent Integrated Braking System) — Seal U

Braking System

DTC C004900 indicates an abnormal brake fluid level detected by the IPB (Intelligent Integrated Braking System).

The fluid level sensor installed in the brake master cylinder reservoir (typically a Hall-effect or float switch) triggers this fault.

The IPB control unit records the fault when the brake fluid level remains continuously below the minimum mark (MIN) or the sensor signal voltage falls outside the calibrated range (normally 0.5V-4.5V, varying linearly with fluid level).

This is a safety-related fault.

When triggered, the system limits ESC, ABS, Automatic Emergency Braking (AEB), and energy recovery functions.

Some models enter limp mode.

Depending on the software version or specific repair scenario, this fault code may also correlate with an abnormal brake pedal position sensor (BPS) signal.

The IPB system verifies brake system integrity by evaluating both the fluid level and pedal signals.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Brake fluid leakage or natural loss: Age-related leaks from the brake calipers, brake lines, IPB integrated pump body, or reservoir seals cause the fluid level to continuously drop below the threshold.
  • 2Brake fluid level sensor fault: Stuck sensor float, damaged Hall element, or failed magnetic float causes the output signal to mismatch the fluid level.
  • 3Electrical connection issues: Sensor connector oxidation, water ingress (common in vehicles driven through water), terminal back-out, or wiring harness damage causing a signal short or open circuit.
  • 4IPB control unit software fault: Missing calibration data, software version defects, or voltage fluctuations causing false codes, commonly occurring when failing to perform system calibration after repairs.
  • 5Brake fluid level sensor installation or reservoir issue: sensor not fully seated, deformed reservoir, or use of non-standard brake fluid causing abnormal sensor readings.
What To Do
  • 1
    Visual inspection: Open the engine compartment and check if the brake fluid reservoir level is below the MIN mark. Inspect the brake fluid color (should be clear and slightly yellow; replace if dark or cloudy).
  • 2
    Leak check: Raise the vehicle and inspect all four brake calipers, brake hoses, steel line fittings, and the bottom of the IPB pump body for wet spots or fluid droplets. Focus on freshly wet areas.
  • 3
    Sensor electrical check: Disconnect the level sensor connector. Measure the supply voltage (should be 5V±0.25V) and ground resistance (should be <1Ω). Check the signal wire for a short to ground or power.
  • 4
    Sensor function test: Use the diagnostic tool to read the level sensor live data stream. Compare the actual fluid level with the sensor voltage (approx. 4.2V at full level, approx. 0.8V at empty level). If the values do not match, replace the sensor.
  • 5
    Wiring harness inspection: Inspect the sensor wiring harness along its route to the IPB control unit. Focus on the front bulkhead grommet and firewall connector for chafing, water ingress, or corrosion. Measure wiring harness continuity.
  • 6
    System calibration: After replacing the sensor, repairing the wiring harness, or adding brake fluid, use VDS2000 to perform the 'Brake Fluid Level Sensor Calibration' and 'IPB System Bleeding' procedures.
  • 7
    Verification test: Clear the fault code and perform a road test (including hard acceleration, hard deceleration, and turning). Observe the data stream for stability, and confirm ESC/ABS functions operate normally and the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM - Poor brake switch contact causing intermittent fault

✓
When driving on rough roads, the dash intermittently showed "Check ESP System" and "Check ABS System" warnings. When the lights came on, automatic emergency braking failed, and the warnings sometimes cleared after cycling the ignition. VDS2000 scan showed DTCs C004900 (Brake Pedal Position Sensor signal abnormal) and U012100. Found slight oxidation inside the brake pedal position sensor connector; measured sensor supply voltage fluctuating between 4.2V and 5V (normal: stable 5V). Confirmed burnt contacts inside the brake light switch causing erratic signal transmission. Replaced the brake light switch assembly (SC-4135100), cleaned the pedal position sensor connector, and applied conductive grease. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Song PLUS DM-i - Brake pedal sensor hardware failure

✓
After sitting overnight, the vehicle showed "Braking System Fault" at startup along with increased brake pedal travel and failed regenerative braking. Stored code C004900. Live data showed brake pedal position sensors 1 and 2 were not maintaining the normal 2:1 voltage ratio: Sensor 1 read 0.8V while Sensor 2 read 0.3V. Removed the pedal position sensor and found the internal Hall element damaged. Replaced the brake pedal assembly (includes pedal position sensor, part number SA-3504010) and performed Brake Pedal Position Calibration with the diagnostic tool. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Han EV - Water ingress corroded sensor connector

✓
After driving through water approximately 30 cm deep, the ESP, ABS, and EPS warning lights illuminated simultaneously. The vehicle would not enter Ready mode and displayed 'Check braking system'. Retrieved DTCs: C004900 (current fault), C003100 (left front wheel speed sensor fault), B1B0100 (airbag system fault). Found the brake pedal position sensor connector at the firewall had water inside with green copper corrosion. Measured the sensor signal wire shorted to ground (0.8 ohms; normal: infinite). Water penetrated the wiring harness grommet during wading, causing the short. Solution: Cleaned the connector terminals with electronic cleaner, applied waterproof silicone grease after drying, replaced the brake pedal position sensor (HAD-3504200), and waterproofed the wiring harness.
Original source ↗
BYD DTC AI Analysis

Tang DM — Software calibration data lost

✓
The dealership replaced the ABS pump. After approximately 50 km of driving, the instrument cluster suddenly displayed "Service ESP". Brake pedal free play increased at the beginning of its travel, and regenerative braking strength decreased. The scanner retrieved DTCs C004900 (Brake Pedal Position Sensor Signal Implausible) and C004800 (Brake Pressure Sensor Fault). No physical damage was found on the new ABS pump or wiring, but live data showed the brake pedal position sensor initial position voltage at 0.7 V, outside the calibration range (normal: below 0.5 V). The brake system had not been recalibrated after the pump replacement, so the control unit could not recognize the pedal's initial position. Solution: Use VDS to perform "Brake Pedal Position Learning" (path: System Calibration → Chassis System → Brake Pedal Position Sensor Calibration). After calibration, voltage read 0.45 V with the pedal released and 4.5 V at full travel. Clearing the fault codes resolved the issue.
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.