AU
C004601

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

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.

The C004601 fault code on the Seal U indicates an abnormal brake master cylinder pressure sensor signal in the ESP system. Severity is medium: basic braking usually remains, but stability control may be limited or disabled. Common causes include a failing internal pressure sensor in the ABS hydraulic modulator or contaminated brake fluid. The recommended fix is diagnosis and repair by an authorised dealer, often requiring ABS modulator replacement. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Aging, damage, or drift of the internal pressure sensor element in the ABS hydraulic modulator (most common; the sensor and pump body are an integrated design and are not replaceable separately)
  • 2Severe brake fluid contamination, degradation, or excessive water content causing inaccurate sensor readings or blockages.
  • 3Poor contact or intermittent 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 does not meet required specifications (non-DOT4 standard).
What To Do
  • 1
    Use a dedicated diagnostic tool (such as BYD VDS or Launch X431) to read the complete fault codes and data stream, check if the pressure sensor live value is abnormal (e.g., displays 0 kPa, a fixed value, or is out of range), and record the freeze frame data.
  • 2
    Check brake fluid quality and level. Inspect for blackening, 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 12 V), ground (resistance <1 Ω), and CAN lines (CAN-H approx. 2.6–2.8 V, CAN-L approx. 2.2–2.4 V, terminal resistance approx. 60 Ω). Measure the circuit for short or open circuits.
  • 4
    Attempt ESP system sensor calibration or a control unit reset (supported on some models). Clear the fault code, perform a road test, and check if the fault reappears after driving a certain distance.
  • 5
    If all above checks are normal 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 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.