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 — Atto 3

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 Atto 3 indicates a medium-severity fault with the right front ABS outlet valve inside the hydraulic control unit. This can reduce anti-lock braking control at the right front wheel during hard braking. Common causes include an open or shorted solenoid valve circuit, or a sticking valve caused by degraded or contaminated brake fluid. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Atto 3
  • 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: typically 2-5Ω)
  • 2Mechanical sticking of the solenoid valve spool. Overdue brake fluid replacement often causes 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 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 defect in the hydraulic modulator assembly, or prolonged vibration causing internal solder joint cracking 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 systemic fault exists.
  • 2
    Perform the hydraulic modulator Actuator Test and listen for a clear electromagnetic 'click' from the right front outlet valve. If no sound occurs, disconnect the HCU wiring harness connector. Measure the solenoid coil resistance between the two terminals of the right front outlet valve. Compare the reading with the workshop manual standard value (usually 2-5 Ω) to check for an open circuit (infinite resistance) or a short circuit (close to 0 Ω).
  • 3
    Check the pins on the ABS hydraulic modulator assembly wiring harness connector (usually located on the top or side of the pump body). Inspect for green oxidation, backed-out pins, spread terminals, or aged sealing rings. Clean with electrical contact cleaner and apply conductive grease.
  • 4
    Measure continuity between the corresponding terminal of the harness-side connector and the ABS ECU, and check 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 yields no response, or if the resistance value changes abnormally after warming up the vehicle, diagnose an internal solenoid valve fault in the HCU. Because the hydraulic control unit assembly is typically a sealed, non-serviceable unit, replace the ABS hydraulic control unit assembly with the attached ECU. Verify the part number is specific to the E5 model (such as the 3550100-xx series).
  • 6
    After replacing the HCU, bleed the brake system (use a diagnostic tool to execute the bleeding procedure to activate the pump motor and valve body cycle). Complete sensor calibration (wheel speed sensor tone ring check) and online coding configuration (Coding). Finally, perform a road test to verify ABS function.
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 Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 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.