AU
C001504

DTC C001504 indicates a circuit or functional fault in the Right Front Outlet Valve inside the Anti-lock Braking System (ABS) Hydraulic Control Unit (HCU) assembly — Seal U

Braking System

DTC C001504 indicates a circuit or functional fault in the Right Front Outlet Valve inside the Anti-lock Braking System (ABS) Hydraulic Control Unit (HCU) assembly.

This solenoid valve is a core component of the ABS actuator.

It opens during the pressure reduction phase of the anti-lock control cycle to release hydraulic pressure from the right front wheel brake cylinder.

The ABS ECU sets this fault code when it detects an open or short circuit in the valve drive circuit, or an abnormal valve spool response (such as sticking or a response timeout).

This fault disables the ABS pressure regulation function for the right front wheel.

During emergency braking, the wheel may lose anti-lock protection and lock up prematurely, severely compromising braking performance and driving safety.

This condition may also trigger a degraded operating mode in related systems, including Electronic Stability Control (ESC) and Automatic Emergency Braking.

The C001504 fault code on the Seal U indicates a medium-severity fault with the right front ABS outlet valve inside the hydraulic control unit. This can be caused by an open or shorted solenoid valve circuit, abnormal coil resistance, or a sticking valve due to contaminated or degraded brake fluid. ABS control for the right front wheel may be reduced. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Open circuit, short circuit, or resistance drift in the internal right front outlet solenoid valve coil of the ABS hydraulic control unit (HCU) assembly (normal range: 2-5 Ω)
  • 2Mechanical sticking of the solenoid valve spool, often caused by overdue brake fluid replacement leading to fluid degradation, crystallization, or contaminant buildup.
  • 3Poor contact, pin corrosion, oxidation, or poor sealing causing moisture ingress at the wiring harness connector between the ABS ECU and the hydraulic modulator assembly.
  • 4ABS ECU internal power drive circuit fault, such as a damaged driver chip (e.g., L9301 series) or related MOSFET breakdown.
  • 5Manufacturing defects in the hydraulic modulator assembly or prolonged vibration causing cracked internal solder joints or valve body leakage.
What To Do
  • 1
    Use the BYD VDS2000 or VDS6000 diagnostic tool to read and confirm DTC C001504 and freeze frame data. Check for accompanying C0010xx series valve body fault codes to determine if a system fault exists.
  • 2
    Perform the hydraulic modulator actuator test (Actuator Test) and listen for a clear solenoid 'click' from the right front outlet valve. If no sound occurs, disconnect the HCU wiring harness connector and measure the solenoid coil resistance between the two terminals of the right front outlet valve. Compare the reading against the repair manual standard value (usually 2-5Ω) to check for an open circuit (infinite resistance) or short circuit (close to 0Ω).
  • 3
    Inspect the pin condition of the ABS hydraulic modulator assembly wiring harness connector (usually located on the top or side of the pump body). Check for green oxidation, backed-out pins, spread terminals, or aging sealing rings. Clean with electrical contact cleaner and apply conductive grease.
  • 4
    Measure continuity between the corresponding terminal on the harness-side connector and the ABS ECU, and check its insulation to ground and power supply to rule out intermittent short or open circuits in the wiring harness.
  • 5
    If all circuit measurements are normal but the actuator test shows no response, or if the resistance value changes abnormally after the vehicle warms up, the HCU internal solenoid valve is faulty. Because the hydraulic control unit assembly is typically sealed and cannot be disassembled for repair, replace the ABS hydraulic control unit assembly with ECU. Verify the part number is specific to the E5 model (e.g., 3550100-xx series).
  • 6
    After replacing the HCU, bleed the brake system (use the diagnostic tool to execute the bleeding procedure to activate the pump motor and cycle the valve body), complete sensor calibration (wheel speed sensor tone ring inspection) and online coding, then perform a road test to verify ABS operation.
Real-World Cases
BYD DTC AI Analysis

BYD E5 front right outlet valve coil open circuit fault

✓
While driving, the ABS and ESC warning lights suddenly came on. Brake pedal feel remained normal. Connected VDS2000 and retrieved DTC C001504. During actuator testing, the right front outlet valve produced no actuation sound; the other three valves operated normally. Disconnected the ABS pump harness connector and measured infinite resistance (open circuit) across the right front outlet valve pins. Diagnosis: burnt solenoid coil inside the HCU. The ABS pump assembly was under warranty, so replaced the genuine ABS hydraulic modulator assembly (with ECU). Performed the bleed procedure and online matching. Fault cleared. Road-tested 20 km with no abnormalities.
Original source ↗
BYD DTC AI Analysis

Chafed BYD E5 ABS pump wiring harness caused intermittent short circuit

✓
The owner reported the ABS warning light tends to come on during rain or after driving through water, sometimes going out automatically in dry weather. The diagnostic scanner logged an intermittent C001504 fault. Inspection revealed the ABS hydraulic modulator assembly wiring harness had chafed at the firewall retaining clip; damaged insulation caused an intermittent short to body on the right front outlet valve drive wire. Technicians repaired the harness (re-soldered the connections and fitted corrugated tubing), adjusted the routing to prevent body interference, and sealed against water ingress. They cleared the fault codes and conducted a simulated rain test; the fault did not return.
Original source ↗
BYD DTC AI Analysis

BYD E5: Brake fluid contamination caused outlet valve sticking

✓
Vehicle entered limp mode with the instrument cluster displaying "Check Brake System" and ABS/ESP warning lights on steady. Diagnosis revealed DTC C001504. Solenoid resistance measured normal at 2.8Ω. Actuator test showed sluggish valve spool movement with occasional faint noise. Owner confirmed brake fluid never changed in 60,000 km. Severe moisture absorption caused the fluid to deteriorate and crystallize, jamming the valve spool. Replaced ABS hydraulic modulator assembly, thoroughly flushed brake system (replacing hoses and wheel cylinders), and refilled with fresh DOT4 brake fluid. Fault cleared.
Original source ↗
BYD DTC AI Analysis

Right front brake line resonance caused valve body weld cracking on BYD E5

✓
ABS warning light illuminates intermittently, more frequently on rough roads. DTC C001504. Found the right front brake hard pipe mounting bracket loose with excessive pipe slack; the line resonated against the body while driving. Long-term vibration transmitted to the ABS pump body caused micro-cracks in the PCB solder joints at the internal right front outlet valve, creating intermittent open circuits. Re-secured the bracket, added vibration dampers to the line, and replaced the ABS hydraulic modulator assembly. Fault eliminated completely.
Original source ↗
BYD DTC AI Analysis

Internal hydraulic modulator defect in new BYD E5

✓
At 8,000 km, the dashboard suddenly displayed "Check Brake System." The ABS, ESC, and automatic emergency braking warning lights illuminated simultaneously; auto hold failed. The dealership diagnosed fault code C001504. Resistance measurement of the right front outlet valve showed 12 Ω (far above the 2–5 Ω specification), indicating an internal inter-turn short in the solenoid coil (partial short). Replaced the OEM ABS hydraulic modulator assembly (part number 3635010-xx). Cleared the fault codes, performed ABS dynamic testing and a 50 km road test. All systems returned to normal.
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.