AU
C055000

DTC C055000 indicates an internal self-check fault in the ABS electronic control unit (ECU) — Seal 6 EV

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.

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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Damaged internal ECU circuit board of the ABS hydraulic modulator assembly: Physical damage to the internal processor, memory, or power management chip causes the self-check procedure 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 located in the engine compartment or near the battery negative terminal) causes reference voltage drift, triggering an ECU false detection or reset.
  • 4Internal communication bus fault: A damaged ECU internal CAN transceiver or LIN communication chip interrupts communication with the vehicle network or causes abnormal communication between internal modules.
  • 5Extreme electromagnetic interference: Electromagnetic pulses from high-power aftermarket electrical devices, non-standard LED headlights, or inverters disrupt normal ECU operation, causing 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 related codes such as C055500 (wheel speed sensor protocol error), and record parameters such as vehicle speed and voltage at the time of the fault.
  • 2
    Check 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 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 the ABS fuse (usually 30A or 40A) for a blown element or 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. Resistance must be <1Ω. Verify ground points G101/G102 (depending on vehicle model) are clean and secure. If necessary, sand to remove rust and apply conductive paste.
  • 5
    Check for wiring short circuits: Inspect the wheel speed sensor power circuit for a short to the main power circuit (according to the BYD workshop manual, the setting conditions for this fault code include 'wheel speed sensor power supply shorted to 12V'). 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 if the fault recurs.
  • 7
    Software update attempt: For some post-2020 models supporting OTA updates or diagnostic tool flashing (such as Song PLUS DMi), attempt to update the ABS control unit software to the latest version (verify TCU version compatibility).
  • 8
    Replace the ABS hydraulic modulator assembly: If all previous checks are normal, confirming internal ECU failure, replace the complete ABS hydraulic modulator assembly including the ECU (part numbers vary by vehicle model; e.g., E5 uses BG-3550100-S). 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 functions correctly and the warning light turns off. Read the DTCs again to confirm C055000 and related fault codes are not present.
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 Seal 6 EV 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.