AU
C108008

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

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.

The C108008 fault code on the Seal U indicates an abnormal signal in the Hill Hold Control brake/gear interlock logic. It is a medium-severity fault because hill start assist may be disabled, increasing rollback risk on slopes and triggering ABS/ESC warnings. Common causes include a faulty or misaligned brake pedal position sensor or an abnormal gear selector position signal. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Poor contact, burnt internal contacts, or misaligned installation of the brake pedal position sensor (brake switch), causing an intermittent signal or abnormal voltage.
  • 2Abnormal gear selector position sensor signal (specifically the P-position lock switch), failing to correctly report the Neutral/Drive position status.
  • 3Loose wiring harness connectors, oxidation from water ingress, or backed-out pins in the connectors between the ABS/ESP control unit and the brake switch and gear position sensor, interrupting signal transmission.
  • 4ABS pump assembly internal signal processing circuit fault; fails to correctly interpret the brake and gear position logic combination signal.
  • 5Vehicle low-voltage battery voltage is too low (below 11V) or the power supply system fluctuates, causing 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) for secure mounting. Check the wiring harness connector for looseness or disconnection. Measure the switch continuity and voltage signal with the pedal pressed and released (the signal should normally switch between 12V/B+ and 0V).
  • 3
    Inspect 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 outputs in the P, R, N, and D positions match 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 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 the insulation to ground (should be greater than 10MΩ).
  • 5
    Check the vehicle low-voltage battery and charging system. Verify the static voltage is at least 12.4V and the dynamic voltage is at least 13.5V to rule out abnormal signal acquisition due to low supply voltage.
  • 6
    If circuit measurements are normal, update 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%: depress the brake pedal and shift to D, then 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

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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 U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.