AU
C055000

DTC C055000 indicates an internal self-check fault in the ABS electronic control unit (ECU) — Atto 3

Braking System

DTC C055000 indicates an internal self-check fault in the ABS electronic control unit (ECU).

Specifically, the control module integrated inside the ABS hydraulic modulator assembly detects a hardware or basic software abnormality.

This constitutes a 'core-level' ABS system fault, indicating the ECU cannot execute normal anti-lock braking control logic.

When triggered, the ABS system forces Fail-Safe Mode.

This disables anti-lock braking, EBD (Electronic Brakeforce Distribution), and ESC (Electronic Stability Control) functions, retaining only conventional hydraulic braking.

The instrument cluster illuminates the ABS warning light, ESC warning light, and brake system warning light.

Some models also display the text prompt 'Please check brake system'.

This DTC differs fundamentally from wheel speed sensor signal faults (such as the C003 series).

The latter represents an 'input signal abnormality', whereas C055000 represents a 'control unit internal abnormality', involving significantly higher repair complexity and cost.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Damage to the ABS hydraulic modulator assembly internal ECU circuit board: Physical damage to the internal processor, memory, or power management chip causes the self-test to fail.
  • 2Abnormal supply voltage: Battery voltage too low (<9V) or too high (>16V), excessive voltage drop in the power supply circuit, or voltage regulator module failure causes the ECU supply voltage to fall outside the normal operating range (typically 12V±0.5V).
  • 3Poor ground circuit: Oxidation, looseness, or corrosion at the ECU main ground point (usually in the engine compartment or near the battery negative terminal) causes reference voltage drift, triggering ECU misjudgment or reset.
  • 4Internal communication bus fault: Damage to the ECU internal CAN transceiver or LIN communication chip interrupts communication with the vehicle network or causes abnormal communication between internal modules.
  • 5Severe electromagnetic interference: Electromagnetic pulses from high-power aftermarket electrical equipment, non-standard LED headlights, or inverters disrupt normal ECU operation, triggering intermittent fault codes.
What To Do
  • 1
    Connect the BYD dedicated diagnostic tool (VDS or ED400). Read the complete DTC list and freeze frame data. Check for accompanying codes such as C055500 (wheel speed sensor protocol error). Record parameters including vehicle speed and voltage at the time of the fault.
  • 2
    Check the battery condition: measure static voltage (should be ≥12.4V), cranking voltage (should be ≥9.6V), and charging voltage (should be 13.5-14.8V). Check the battery terminals for oxidation. Perform a battery load test if necessary.
  • 3
    Check the ABS system power supply: Disconnect the ABS hydraulic modulator assembly connector and measure the voltage between the power terminal (usually pin 1 or 25; refer to the vehicle wiring diagram) and ground. The voltage must be within 12V±0.5V. Check if the ABS fuse (usually 30A or 40A) is blown or has poor contact.
  • 4
    Check the ECU ground circuit: Use a multimeter to measure the resistance between the ECU ground terminals (usually pins 13 and 38) and the battery negative terminal. The resistance must be <1 Ω. Verify ground points G101/G102 (depending on vehicle model) are clean and tight. If necessary, sand off rust and apply conductive paste.
  • 5
    Check for wiring short circuits: Test the wheel speed sensor power circuit for a short to the main power circuit (per the BYD workshop manual, the setting conditions for this fault code include 'wheel speed sensor power supply shorted to 12V detected'). Focus on wiring harness wear points.
  • 6
    Eliminate electromagnetic interference: Remove recently installed electrical accessories in the vehicle, such as inverters, high-power audio systems, and non-standard LED lights. Clear the fault code, road test the vehicle, and observe whether the fault recurs.
  • 7
    Software flash attempt: For post-2020 models supporting OTA updates or diagnostic tool flashing (e.g., Song PLUS DMi), flash the ABS control unit software to the latest version (verify TCU version compatibility).
  • 8
    Replace the ABS hydraulic modulator assembly: If all above checks are normal, confirming internal ECU damage, replace the entire ABS hydraulic modulator assembly with ECU (part numbers vary by vehicle model, e.g., BG-3550100-S for E5). Note: After replacement, use a diagnostic tool to perform the 'Bleeding Procedure', 'Wheel Speed Sensor Signal Check', and 'G Sensor/Yaw Rate Sensor Calibration'.
  • 9
    Final verification: Clear all DTCs, drive straight at speeds above 20 km/h, and apply the brakes multiple times. Verify the ABS operates normally and the warning lamp turns off. Read the DTCs again to confirm C055000 and related fault codes do not return.
Real-World Cases
BYD DTC AI Analysis

2019 BYD E5 ABS Pump Assembly Internal Damage Case

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Vehicle: 2019 BYD E5, 85,000 km. Symptoms: ABS and ESP warning lights suddenly lit up while driving. Instrument cluster showed "Check brake system" and brake pedal became stiff. Diagnosis: VDS scan retrieved DTC C055000 (ABS ECU fault). Freeze frame: 45 km/h, 13.8 V. Battery, fuses and ground tested normal. Power reset did not clear the code. Power and ground at ABS pump connector measured normal. Internal ECU in ABS hydraulic modulator assembly failed. Repair: Replaced ABS hydraulic modulator assembly with integrated ECU (part number BG-3550100-S). Bled brake system and calibrated wheel speed sensors. Fault cleared. Cost: Parts approx. 1800 yuan, labor 400 yuan.
BYD DTC AI Analysis

Poor ground in Song Plus DM-i causes intermittent C055000 fault

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Vehicle: 2021 BYD Song PLUS DM-i, 32,000 km. Symptoms: ABS warning light intermittently comes on when driving on rough roads; goes off after restarting. Highway driving is normal. Diagnosis: Scanner retrieved stored fault codes C055000 and C055500 (left front wheel speed sensor protocol error); no active faults present. Inspection found the ABS pump ground point G101 on the left front side member had a slightly loose mounting bolt and white oxidation on the mating surface. Vibration caused ground resistance variations, resulting in abnormal ECU supply voltage and triggering internal protective fault codes. Repair: Removed the ground wire, sanded the ground point and harness terminal to bare metal, applied conductive paste, and tightened the bolt to the specified torque of 10 N·m. Cleared the fault codes and test-drove 20 km; the fault did not return.
BYD DTC AI Analysis

E5 Taxi Battery Aging Caused ABS ECU Fault

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Vehicle: 2018 BYD E5 taxi, 240,000 km. Symptoms: ABS warning light on during cold morning starts, went out after 10 minutes of driving, but recently stayed on continuously. Diagnosis: DTC C055000 stored. Freeze frame showed 10.2V fault voltage. Measured static battery voltage at 11.8V (low). Load test showed battery capacity at only 45% of rated value with high internal resistance. Battery degradation caused voltage sag during startup, triggering ABS ECU low-voltage protection. Repair: Replaced AGM battery (12V 60Ah), cleaned ABS ground points, cleared codes. Monitored for three consecutive days—no recurrence. Note: The 12V auxiliary battery in pure electric vehicles is equally critical. Inspect and replace every 2-3 years.
BYD DTC AI Analysis

ABS ECU internal short circuit after water ingress

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Vehicle: BYD Song Pro DM, 50,000 km. Background: Drove through standing water (~40 cm deep). ABS light stayed on next day. Diagnosis: Scan tool read DTC C055000; the code would not clear. The ABS hydraulic modulator sits on the left side of the engine bay. Despite the high mounting position, water splashed into the connector during the crossing, leaving moisture inside the plug. Insulation resistance between the ABS pump power terminal and ground measured only 2 MΩ (normal >10 MΩ), indicating the internal circuit board had shorted from moisture. Resolution: Replaced the ABS hydraulic modulator assembly and the oxidized harness connector. Sealed the surrounding wiring with insulating silicone grease. Fault cleared. Recommendation: Check the ABS pump connector seal after driving through water.
BYD DTC AI Analysis

Modified inverter causing false EMI detection

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Vehicle: 2018 BYD E5, 60,000 km. Symptoms: After installing a 2000W high-power onboard inverter, the ABS warning light illuminates intermittently when the inverter is in use; the fault disappears when the inverter is switched off. Diagnosis: Retrieved DTC C055000 with no accompanying faults. Checked ABS power supply, ground, and wiring—all normal. Determined that high-frequency electromagnetic pulses generated during inverter operation interfere with the ABS ECU through power lines or radiated emissions. Solution: Removed the non-factory inverter and switched to the BYD dedicated 12V power outlet (cigarette lighter socket, maximum 120W), or added a shielding cover to the inverter with independent ground. Cleared the fault codes and tested repeatedly; the fault did not recur. Note: The ABS ECU is sensitive to electromagnetic interference; avoid high-power non-standard electrical devices.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.