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 8

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 8 indicates a medium-severity fault with the right front ABS outlet valve inside the hydraulic control unit. This can stop proper ABS pressure control at the right front wheel, increasing lock-up risk during hard braking. Common causes include an open or shorted solenoid coil, or a sticking valve due to degraded brake fluid contamination. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 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 2-5 Ω)
  • 2Mechanical sticking of the solenoid valve spool, often resulting from prolonged failure to replace brake fluid, causing fluid degradation, crystallization, or contaminant buildup.
  • 3Poor contact, pin corrosion, oxidation, or moisture ingress due to poor sealing 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 defect 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 system fault exists.
  • 2
    Perform the hydraulic modulator Actuator Test and listen for a clear 'click' from the right front outlet valve solenoid. If the valve makes 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 with the workshop manual standard value (usually 2-5Ω) to check for an open circuit (infinite resistance) or a 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 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 circuit measurements are normal but the actuator test shows no response, or if the resistance value changes abnormally after the vehicle warms up, diagnose an internal solenoid valve fault in the HCU. Because the hydraulic control unit assembly is 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 (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 cycling). 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 8 Fault Codes
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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.