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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 — Qin Plus

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.

5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 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)
  • 2Mechanically stuck solenoid valve spool. Prolonged failure to replace the brake fluid often degrades the fluid, causing crystallization or impurity deposits.
  • 3Poor contact, pin corrosion, oxidation, or poor sealing resulting in 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 long-term vibration causing cracked internal solder joints and 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 there is no sound, 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 to the workshop manual standard value (usually 2-5Ω) and check for an open circuit (infinite resistance) or a short circuit (close to 0Ω).
  • 3
    Inspect the pins of the ABS hydraulic modulator assembly wiring harness connector (usually on the top or side of the pump body). Check for green corrosion, 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 of the harness-side connector and the ABS ECU, and check insulation to ground and power supply to eliminate intermittent harness short or open circuit faults.
  • 5
    If all circuit measurements are normal but the actuator test yields no response, or the resistance value changes abnormally after the vehicle warms up, diagnose an internal HCU solenoid valve fault. Because the hydraulic control unit assembly is typically sealed and cannot be disassembled for repair, replace the ABS hydraulic control unit assembly with the attached 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 valve body circulation. 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 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.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.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.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.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.