AU
C004601

DTC C004601 indicates an abnormal brake master cylinder pressure sensor signal in the ESP (Electronic Stability Program) system — Qin Plus

Braking System

DTC C004601 indicates an abnormal brake master cylinder pressure sensor signal in the ESP (Electronic Stability Program) system.

This sensor integrates into the ABS hydraulic modulator (pump unit) and monitors brake system hydraulic pressure in real time, providing key input signals for ESP, HDC (Hill Descent Control), and AEB (Automatic Emergency Braking).

A pressure signal outside the normal range (such as an open circuit, short circuit, signal drift, or delayed response) triggers this fault code.

This limits or disables the ESP function, affecting vehicle stability control, but basic braking usually remains unaffected.

Clearing the code will not resolve this hardware-level fault.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Aging, damage, or drift of the internal pressure sensor element in the ABS hydraulic modulator (most common; the sensor and pump body are integrated and require replacement as a complete assembly).
  • 2Severe contamination, degradation, or excessive water content in the brake fluid causing distorted sensor readings or blockage.
  • 3Poor contact or loose connection in the ABS pump power supply circuit or ground point, causing abnormal sensor supply voltage.
  • 4Interference, short circuit, or open circuit in the CAN communication line causes abnormal pressure signal transmission.
  • 5Incomplete brake system bleeding after repair, or brake fluid specification does not meet requirements (not DOT4 standard).
What To Do
  • 1
    Use a dedicated diagnostic tool (such as BYD VDS or Launch X431) to read complete fault codes and the data stream. Check if the pressure sensor real-time value is abnormal (e.g., displays 0 kPa, a fixed value, or out of range), and record freeze frame data.
  • 2
    Check the brake fluid quality and level. Inspect for darkening, cloudiness, or contaminants. If necessary, completely replace with DOT4 brake fluid and thoroughly bleed the brake system.
  • 3
    Check the connection status of the ABS pump assembly power supply (constant 12V), ground (resistance <1Ω), and CAN lines (CAN-H approx. 2.6-2.8V, CAN-L approx. 2.2-2.4V, terminal resistance approx. 60Ω). Test the wiring for short or open circuits.
  • 4
    Calibrate the ESP system sensors or reset the control unit (on supported models). Clear the fault code, perform a road test, and observe if the fault reappears after driving a certain distance.
  • 5
    If all above checks pass and the fault persists, the ABS pump internal sensor is damaged. Replace the ESP hydraulic modulator assembly with ECU. After replacement, perform control unit coding, wheel speed sensor calibration, and lateral acceleration sensor calibration.
Real-World Cases
BYD DTC AI Analysis

BYD Song – ABS Pump Internal Pressure Sensor Damaged

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While driving, the instrument cluster simultaneously displayed C00408 (brake pedal switch signal fault) and C004601 (pressure sensor fault), the ESP warning light came on, and the driver felt both rear wheels dragging with noticeably increased resistance. The technician first checked the wiring and found no open or short circuits. Live data from the diagnostic scanner showed the pressure sensor signal stuck at an abnormal fixed value that did not change with brake pedal input. This confirmed an internal pressure sensor failure in the ABS pump. Since the sensor is integrated into the pump body and cannot be replaced separately, the technician replaced the ABS pump assembly, calibrated the system, and cleared the fault.
Original source ↗
BYD DTC AI Analysis

BYD SUV - Intermittent ESP/HDC warning lights while driving

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No warning lights at startup. HDC (Hill Descent Control) and ESP warning lights come on after driving several tens of metres. Scanner reports DTC C004601. Live data shows normal wheel speeds for all four wheels while driving; driver reports normal brake pedal feel. Suspected causes: 1) Insufficient brake pressure, 2) Wiring fault, 3) ABS pump failure, 4) Wheel speed sensor signal error. Checked ABS pump power and ground — normal. CAN communication normal. System pressure data did not match actual brake pressure; signal drift present. Pressure sensor is integrated into the ABS pump. Replaced ABS pump assembly. Fault cleared.
Original source ↗
BYD DTC AI Analysis

BYD E5 - Brake fluid contamination caused false pressure sensor readings

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The vehicle logged DTC C004601. The technician was initially unsure where the 'pressure sensor' was located (it is actually integrated within the ABS pump). Technical guidance instructed them to check brake fluid condition first; they found the fluid severely blackened with water content over 3%. Contaminated fluid can cause abnormal sensor signal detection. They also checked power supply, ground, and communication lines to the ABS module assembly — all were normal. They recommended thoroughly replacing the brake fluid and flushing the lines first. After the replacement, the fault code did not return. If the fault persists, replace the ABS module assembly.
Original source ↗
BYD DTC AI Analysis

BYD Technical Documentation — Standard Diagnostic Procedure for C0046 Series DTCs

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Within the C0046 (pressure sensor fault) series, C004601 indicates a brake pressure sensor signal error or performance fault. Per the BYD ESP system workshop manual, this sensor monitors brake master cylinder pressure to provide critical data for ESP and HDC functions. The code sets when the sensor detects pressure signals outside physical limits (such as negative values or over-range readings), abnormal change rates, or logical inconsistencies with other sensors. The pressure sensor is internal to the ABS pump assembly; the manual does not support individual repair or replacement and mandates replacing the complete ABS pump assembly (hydraulic modulator with ECU).
Original source ↗
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.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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.