AU
C108008

C108008 indicates the Hill Hold Control (HHC) system detects an abnormal clutch/start interlock signal — Seal 6 EV

Braking System

C108008 indicates the Hill Hold Control (HHC) system detects an abnormal clutch/start interlock signal.

In the BYD E5 battery electric vehicle, this fault does not refer to a conventional mechanical clutch.

Instead, it indicates the ABS/ESP control unit fails to receive the correct brake pedal-gear interlock logic signal (the combined signal the system uses to determine if the vehicle is in a 'ready to move off' state).

The HHC system relies on the brake switch signal, gear position signal (P/R/N/D status), and wheel speed signals.

When the control unit detects a released brake pedal while the gear signal or brake interlock signal contradicts the hill hold release logic, it logs a clutch signal fault.

This fault disables the hill start assist function.

The vehicle may roll backward on a slope when the driver transitions from the brake pedal to the accelerator pedal.

The fault also illuminates the ABS/ESC fault warning lamp and compromises driving safety.

4
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Poor contact, burnt internal contacts, or misalignment of the brake pedal position sensor (brake switch), causing intermittent signals or abnormal voltage.
  • 2Abnormal signal from the gear selector position sensor (especially the Park lock switch), failing to correctly report Neutral/Drive gear status.
  • 3Wiring harness connectors between the ABS/ESP control unit and the brake switch or gear position sensor are loose, oxidized from water ingress, or have backed-out pins, interrupting signal transmission.
  • 4Internal signal processing circuit fault in the ABS pump assembly; cannot correctly interpret the brake and gear position logical combination signal.
  • 5Vehicle low-voltage battery voltage is too low (below 11V) or power supply system fluctuations cause logic errors during control unit signal acquisition.
What To Do
  • 1
    Connect the BYD dedicated diagnostic tool (VDS or ED-400), read the DTC C108008 freeze frame data, and record the vehicle speed, brake pedal status, gear position, and longitudinal acceleration value when the fault occurred.
  • 2
    Visually inspect the brake pedal position sensor (brake light switch) mounting, check the wiring harness connector for looseness or disconnection, and measure the switch continuity and voltage signal with the pedal pressed and released (the signal normally switches between 12V/B+ and 0V).
  • 3
    Check the gear position sensor connector below the shift control mechanism. Measure the resistance and voltage of the P position lock signal and gear position signal. Verify the signal output in the P, R, N, and D positions matches the workshop manual standard values.
  • 4
    Disconnect the ABS pump assembly connector (located on the right side of the engine compartment or near the front compartment power distribution box). Check the pins for oxidation, water ingress, or deformation. Measure the continuity of the brake switch signal wire and gear position signal wire to the ABS control unit (should be less than 1Ω) and their insulation to ground (should be greater than 10MΩ).
  • 5
    Check the vehicle low-voltage battery voltage and charging system. Verify the static voltage is at least 12.4V and the dynamic voltage is at least 13.5V to rule out signal acquisition faults caused by low power supply voltage.
  • 6
    If circuit measurements are normal, reflash the ABS/ESP control unit software or reset the parameters (if supported). If the fault persists, replace the ABS pump assembly (integrated ESP control unit).
  • 7
    After repairing or replacing the faulty component, clear the fault code and verify the HHC function on a slope greater than 3%: press the brake pedal and shift to D, release the brake pedal, and confirm the vehicle remains stationary for 2-3 seconds without rolling backward and no fault indicator illuminates.
Real-World Cases
BYD DTC AI Analysis

E5: Oxidised brake switch contacts caused intermittent HHC failure

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2019 BYD E5, 42,000 km. Dash intermittently showed ABS and ESC warning lights. Read fault code C108008. Inspection found the brake pedal position sensor (four-wire brake switch) had slightly burnt internal contacts, causing 0.3–0.5 s signal dropouts on rough roads. Replaced the brake switch assembly. Read the brake pedal signal data stream; cycled the pedal 20 times with normal switching. Tested HHC hill-start assist on a slope; function restored. Fault resolved.
BYD DTC AI Analysis

E5 front compartment wiring harness chafed through, causing clutch signal short circuit

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2018 E5 taxi, 80,000 km, ABS warning light on continuously, DTC C108008 would not clear. Inspection found the wiring harness below the ABS pump connector rubbing against the front compartment bracket, with the brake switch signal wire insulation worn through and shorted to ground. This caused the ABS control unit to continuously receive an incorrect brake-applied signal. Repaired the damaged harness, re-wrapped and rerouted the wiring to eliminate interference, cleared the fault code, and restored normal operation.
BYD DTC AI Analysis

E5 Gear Position Sensor Drift Caused HHC Signal Fault

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A 2019 E5 rolled back during a hill start, with the dashboard displaying 'Check Braking System'. The scan tool read DTC C108008. Live data showed the gear position signal fluctuating between N and D when Drive was engaged. Disassembling the shift mechanism revealed the gear position sensor mounting screws had loosened, allowing the sensor to shift relative to the shift shaft. Recalibrating the sensor and tightening the screws stabilized the signal and resolved the fault.
BYD DTC AI Analysis

E5: Low-voltage battery discharge caused abnormal signal acquisition

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2018 E5 started after one week parked. Multiple warning lights illuminated: ABS, ESC, and powertrain system. Retrieved DTC C108008 and multiple communication fault codes. Low voltage battery measured 10.8V. Voltage returned to normal after charging. Cleared fault codes; C108008 did not reappear. Diagnosed as discharged battery causing ABS control unit voltage drop at startup, falsely detecting abnormal brake signal. Recommended owner replace the aging battery.
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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV overview →
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.