AU
C008208

C008208 is a sub-fault code for the BYD ABS/ESP system — Seal U

Braking System

C008208 is a sub-fault code for the BYD ABS/ESP system.

C0082 indicates an abnormal brake system status, and sub-code 08 identifies the specific signal anomaly type.

The ABS (or ESP) control unit sends this abnormal brake system status warning to the instrument cluster.

It typically indicates abnormal communication signals between the control unit and the instrument cluster, key brake system sensor signals falling outside the valid range, or a protective warning triggered by prolonged continuous ESP intervention.

This DTC indicates the ABS/ESP system may fail to operate normally.

The vehicle will lose active safety functions including anti-lock braking, electronic stability control, and automatic emergency braking.

Conventional hydraulic braking typically remains unaffected.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose connection, oxidation, or poor contact in the ABS/ESP control unit power supply or ground circuit, causing intermittent abnormal operation of the control unit.
  • 2CAN bus communication fault (including short circuit, open circuit, or signal interference on the powertrain CAN or chassis CAN), causing interrupted communication or abnormal data between the ABS control unit, instrument cluster, and VCU.
  • 3Abnormal wheel speed sensor signal (damaged sensor, worn or shorted wiring, dirty tone ring) causing the ABS control unit to receive an implausible wheel speed difference signal.
  • 4Abnormal brake pedal position sensor (or brake light switch) signal caused by installation misalignment, contact oxidation, or poor wiring connection, resulting in incorrect pedal status recognition.
  • 5Internal receiving circuit fault in the instrument panel or software version mismatch causing a false brake system fault warning.
What To Do
  • 1
    Connect the VDS diagnostic tool and read all fault codes. Check for accompanying C0031-C0048 (wheel speed sensor faults), C0051 (steering wheel angle fault), or U-class communication fault codes, and record the freeze frame data.
  • 2
    Check the instrument panel warning lights (ABS, ESP, EBD, brake system fault light), verify the fault symptom matches the DTC, and check the brake fluid level.
  • 3
    Check the power supply (constant power and ignition power) and ground harness connectors of the ABS/ESP control unit (usually located in the engine compartment or near the cabin firewall). Measure the voltage; it must be within 12V ± 0.5V. Check the terminals for oxidation or backed-out pins.
  • 4
    Measure the voltage and waveform of the diagnostic CAN (CAN-H approximately 2.6-2.8 V, CAN-L approximately 2.2-2.4 V, terminal resistance approximately 60 Ω) and chassis CAN circuits. Check the wiring harness for wear or interference with the vehicle body.
  • 5
    Check the resistance of all four wheel speed sensors (approximately 1.0-1.5 kΩ) and the signal voltage (expect a 0-5V AC voltage change when rotating the wheel). Check the gap between the sensor and the tone ring, and inspect the tone ring surface for dirt or damage.
  • 6
    Check the installation position of the brake pedal position sensor (or brake light switch), test the switch on/off logic, and inspect the wiring harness for wear.
  • 7
    Perform a power-off reset on the ABS/ESP control unit (disconnect the negative battery terminal for 5 minutes). Clear the fault code, then perform system calibration (including calibration of the longitudinal acceleration sensor, lateral acceleration sensor, and steering wheel angle sensor).
  • 8
    Perform a road test (including straight-line driving, turning, and braking tests) and observe if the fault code reappears. Use VDS to read the wheel speed data stream in real time and confirm there are no abnormal jumps.
Real-World Cases
BYD DTC AI Analysis

Loose ESP control unit connector causes intermittent C008208

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Symptoms: Dashboard intermittently displayed "Check ESP System" and "Check ABS System" warnings. DTC C008208 appeared sporadically, with increased frequency on rough roads. Brake pedal feel remained normal. Diagnosis: Scanned the brake system with VDS and retrieved DTC C008208; history showed it as a current fault. Brake fluid level was normal and live data from all four wheel speed sensors read normally. Inspected power and ground at the ESP control unit (left side of engine bay) and found poor contact at the main connector, a loose locking clip, and slightly oxidised internal terminals. Resolution: Re-seated the ESP control unit connector, cleaned the terminals with electronic contact cleaner, applied conductive grease, and replaced the locking clip to ensure a secure connection. Cleared the fault codes and completed a continuous 50 km road test; the fault did not reoccur.
BYD DTC AI Analysis

Worn right front wheel speed sensor wiring harness causing abnormal signal

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Symptoms: Dashboard suddenly displayed "Brake System Fault" while driving. ESP and ABS warning lights both lit up. Vehicle speed intermittently restricted (limp mode). Fault code: C008208. Diagnosis: Scanner showed only C008208 (Brake System Abnormal), no specific wheel speed sensor codes. Live data showed right front wheel speed signal fluctuating intermittently (2-3 km/h) while stationary. Raised the vehicle and found the right front wheel speed sensor harness rubbing against suspension components near the steering knuckle. Insulation worn through, causing intermittent short-to-ground in the signal wire. Solution: Cut out the damaged section of right front wheel speed sensor harness, resoldered connections, and insulated with heat shrink tubing. Rerouted and secured harness with cable ties to avoid suspension contact. Cleared fault codes and performed ABS dynamic test. Fault resolved.
BYD DTC AI Analysis

Misaligned brake pedal switch causing false signal

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Symptoms: At startup, dashboard displayed "Check braking system" with warning light on. Brake lights worked normally when pedal pressed; braking function normal. DTC C008208 stored. Diagnosis: Retrieved DTC C008208; no other codes present. Checked brake pedal position sensor live data: signal remained "pressed" when pedal fully released (normally closed contacts not opening). Found brake pedal switch mounting bracket deformed (switch located above pedal), causing insufficient clearance between switch and pedal linkage; switch did not fully release when pedal returned. Resolution: Adjusted brake pedal switch position until contacts opened properly with pedal fully released (faint click heard), then tightened mounting nuts. Ran brake system calibration (brake pedal position learning via VDS), cleared codes, road test normal.
BYD DTC AI Analysis

Faulty instrument panel CAN communication caused false fault signal reception.

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Symptoms: After starting the vehicle, the instrument cluster displayed a brake system fault and the ABS light stayed on. The diagnostic tool showed no fault codes in the ABS system; only the instrument cluster reported U-type communication faults (lost communication with ABS). Diagnosis: CAN bus voltage at the ABS control unit measured normal. At the instrument cluster, CAN-H and CAN-L voltages were both approximately 2.5V with no fluctuation, indicating a loose connection. Inspection revealed a backed-out terminal in the instrument cluster wiring harness connector X10 (behind the instrument cluster), causing unstable CAN signal transmission. Solution: Repaired the instrument cluster wiring harness connector X10, re-crimped the CAN wire terminals, and ensured proper seating. Cleared all system fault codes. The instrument cluster brake system warning light went off and C008208 did not reappear.
BYD DTC AI Analysis

Unstable battery voltage caused the ABS control unit to reset abnormally

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Symptoms: After sitting overnight, the vehicle started with the dashboard showing multiple system faults (ABS, ESP, brake system). Fault codes included C008208 and multiple U-class communication faults. Some warning lights cleared on their own after driving briefly. Diagnosis: Battery voltage measured 12.1V at rest (low) and dropped to 9.2V during cranking (too low). Checked the ABS control unit power supply and found severe oxidation at the battery negative ground point. This caused insufficient voltage to the control unit during startup, triggering a reset. Resolution: Cleaned and tightened the battery negative ground point, applied conductive grease to prevent oxidation, and replaced the aging battery (insufficient capacity). Startup testing showed voltage stayed above 11V. Cleared all fault codes with no recurrence.
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.