AU
C004008

DTC C004008 indicates the ABS/ESC control unit detected an abnormal Brake Pedal Switch signal — Atto 8

Braking System

DTC C004008 indicates the ABS/ESC control unit detected an abnormal Brake Pedal Switch signal.

The Brake Pedal Switch typically contains primary and secondary contact sets (a normally open/normally closed combination) to provide hard-wired driver braking intent signals to the Vehicle Control Unit (VCU) and the ABS module.

These signals directly affect brake light control, regenerative braking cancellation, Auto Hold logic, and vehicle power-up (Ready) permission.

This DTC sets when the ABS module detects the switch signal voltage, logic combination (whether primary and secondary signals are mutually exclusive), or signal change rate exceeds calibrated thresholds.

Potential causes include a single-circuit open, simultaneous dual-circuit short, signal desynchronization, or internal switch failure.

A persistent fault causes abnormal regenerative braking, ESP function degradation, and brake lights stuck on or off.

Extreme conditions trigger vehicle limp mode or prevent vehicle power-up.

The C004008 fault code on the Atto 8 indicates an abnormal brake pedal switch signal detected by the ABS/ESC control unit. Severity is medium, as it can affect brake lights, regenerative braking, ESP operation, Auto Hold, or vehicle Ready status. Common causes include internal brake switch failure, worn contacts, water ingress, corrosion, or loose connector pins. The recommended fix is to 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 — Atto 8
  • 1Burnt internal contacts, spring fatigue, or Hall element failure inside the brake pedal switch prevents the signal from switching on and off normally.
  • 2Aged switch connector seal allows water ingress, causing oxidation (green copper corrosion) or terminal pin back-out, resulting in intermittent poor contact.
  • 3Wiring harness chafed or damaged near the firewall, steering column, or pedal mechanism, causing a short to ground or short to power.
  • 4Worn pedal mechanism rubber pad or deformed mounting bracket creates an excessive gap between the switch pushrod and the pedal (normal preload gap: 0.5-1.0mm), causing marginal signal trigger failure.
  • 5ABS/ESC control unit internal signal acquisition circuit fault or software logic error (less common; consider only after ruling out external wiring).
What To Do
  • 1
    Use the diagnostic tool to read freeze frame data. Verify vehicle speed, pedal status, and main and secondary switch signal logic at the time of the fault to determine if the fault is static or dynamic intermittent.
  • 2
    Visually inspect the physical installation of the brake pedal switch. Verify the retaining clip is intact and the push rod shows no excessive wear. Check the wiring harness for interference during full pedal travel and at steering wheel limit positions.
  • 3
    Disconnect the switch connector. Measure the power supply pin voltage (should be 12V/B+) and ground circuit resistance (should be <1Ω) to rule out power or ground faults.
  • 4
    Use a multimeter to measure the continuity logic of the switch main and auxiliary contacts: when releasing the pedal, the main contact should be open and the auxiliary contact closed; when pressing the pedal, the states should reverse. Alternatively, use an oscilloscope to capture signal changes and check for glitches or delays.
  • 5
    Measure continuity between the switch wiring harness and the ABS pump connector (resistance <1Ω) and insulation to ground/power (resistance >10MΩ). Focus inspection on the wiring harness at the firewall grommet and under the instrument panel.
  • 6
    After replacing the switch, some models require brake pedal position learning or ESC system calibration. Clear the fault code and perform a road test to confirm the brake signal in the data stream synchronizes with pedal movement and shows no spikes.
Real-World Cases
BYD DTC AI Analysis

BYD E5 - Internal open circuit in brake pedal switch

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Symptoms: Vehicle would not enter Ready mode. Instrument cluster displayed "Check braking system" and brake lights did not illuminate. Current fault code C004008 present. Data stream showed both brake pedal primary and secondary signals as "not depressed". Diagnosis: Disconnected pedal switch connector. Measured switch internal contacts with multimeter. Resistance remained infinite with pedal both depressed and released (normal: 0Ω/∞Ω toggle). Confirmed switch internal contacts burnt open. Solution: Replaced brake pedal switch (part cost: 45-65 yuan). Reconnected connector. Vehicle powered up normally and brake lights functioned. Cleared fault codes; ABS self-check passed.
BYD DTC AI Analysis

BYD Qin Pro DM - Water ingress into connector caused oxidation and intermittent fault

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Symptoms: ABS/ESP warning light intermittently illuminates while driving, accompanied by sudden loss of regenerative braking. DTC C004008 stored as history. Occurs frequently in rainy weather or after water crossings. Diagnosis: Inspected the switch connector beneath the dashboard on the pedal bracket. Found green corrosion on internal pins from car wash or AC water leakage. Wiggling the harness caused brake signal fluctuation in live data. Solution: Cleaned connector pins with electrical contact cleaner, applied conductive grease, and replaced the seal. Reconnected the plug and secured the harness above the bracket with cable ties to prevent sagging. No recurrence at one-month follow-up.
BYD DTC AI Analysis

BYD Song PLUS EV - Pedal mechanism wear causing abnormal signal gap

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Symptoms: Above 80 km/h or during light braking, the instrument cluster intermittently displayed "Check ESP System". DTC C004008 (signal implausible) set. City driving at low and medium speeds remained normal. Diagnosis: Inspected the brake pedal mechanism and found the pedal return buffer rubber pad severely worn. The switch plunger could not fully extend after pedal release, leaving the primary and secondary signals marginal. Measured switch plunger travel at only 0.2 mm (specification requires >0.5 mm). Solution: Replaced the pedal mechanism buffer pad. Readjusted the switch mounting position to ensure 0.8 mm preload clearance. Tightened the locknut to 8–10 N·m. Road-tested under high-speed braking and light braking conditions; fault resolved.
BYD DTC AI Analysis

BYD Tang DM - Wiring harness interference with steering column causes wear and short circuit

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Symptoms: Intermittent failure to enter Ready mode. Instrument cluster simultaneously displays "Check Brake System" and "Check ESP." Scanner reads DTCs C004008 (main signal) and C004108 (secondary signal). Diagnosis: Inspected firewall-to-dashboard harness. Retaining clip had detached, allowing harness to rub against steering column universal joint when turning wheel or pressing pedal. Cutting open the sheath exposed copper strands on two signal wires with short-circuit damage. Solution: Cut out damaged 20cm section. Resoldered wires and applied double-layer heat shrink tubing. Rerouted harness and secured with dedicated clip to bracket away from steering column. Verified no interference through full steering and pedal travel.
Other Atto 8 Fault Codes
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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.