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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.

4
Cases Logged
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
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.