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C108008

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

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 — Qin Plus
  • 1Poor contact, burnt internal contacts, or misaligned installation of the brake pedal position sensor (brake switch), causing an intermittent signal or abnormal voltage.
  • 2Abnormal signal from the gear selector position sensor (especially the Park lock switch), failing to correctly indicate Neutral/Drive gear status.
  • 3Loose harness connectors, oxidation due to water ingress, or backed-out pins between the ABS/ESP control unit, brake switch, and gear position sensor, interrupting signal transmission.
  • 4ABS pump assembly internal signal processing circuit fault, unable to 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 freeze frame data for DTC C108008, 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. Measure switch continuity and the voltage signal with the pedal pressed and released (normal operation switches between 12V/B+ and 0V).
  • 3
    Check the gear position sensor connector below the gear selector mechanism. Measure the resistance and voltage of the P position lock signal and gear position signal. Verify the signal outputs in the P, R, N, and D positions meet the standard values in the workshop manual.
  • 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 terminals 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 low supply voltage as the cause of signal acquisition abnormalities.
  • 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 light illuminates.
Real-World Cases
BYD DTC AI Analysis

E5: Oxidised brake switch contacts caused intermittent HHC failure

✓
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 Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.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 Qin Plus →Qin Plus 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.