AU
C003504

DTC C003504 indicates a right front wheel speed sensor (RF Wheel Speed Sensor) circuit or signal abnormality, specifically low sensor supply voltage, signal voltage out of range, or compromised circuit integrity — Seal U

Braking System

DTC C003504 indicates a right front wheel speed sensor (RF Wheel Speed Sensor) circuit or signal abnormality, specifically low sensor supply voltage, signal voltage out of range, or compromised circuit integrity.

In the BYD ABS/ESP system, this fault prevents the control unit from obtaining an accurate right front wheel speed signal and triggers limp mode.

Effects include: ABS function disabled, ESP deactivated, EBD malfunction, automatic emergency braking (AEB) function limited, regenerative braking efficiency reduced or disabled, and cruise control unavailable.

This DTC is a hard fault.

The control unit triggers this code upon continuously detecting the abnormality with the ignition switch in the ON position or while driving.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wheel speed sensor component fault: Internal coil open/short circuit, abnormal electromagnetic sensor resistance (normal: 1.0-1.5kΩ), abnormal Hall-effect sensor power supply, or internal circuit damage resulting in weak or distorted signal output.
  • 2Wiring and connector issues: sensor plug oxidation, water corrosion, loose terminals; worn harness insulation causing a short to ground or intermittent open circuit; engine compartment high temperatures causing harness aging and cracking, especially where a loose retaining clip on the right front longitudinal beam allows the harness to rub against the vehicle body.
  • 3Abnormal mechanical installation and clearance: Sensor-to-tone ring (reluctor ring) gap is too large (standard: 0.3-1.2 mm) or too small (causing rubbing); a loose or damaged right front wheel bearing causes tone ring radial runout to exceed tolerance (>0.1 mm), preventing the sensor from detecting a stable signal.
  • 4Signal tone ring contaminated or damaged: brake dust, iron shavings, or muddy water adhering to the tone ring surface; broken, missing, or deformed tone ring teeth (common after accident repairs or prolonged water exposure), causing irregular changes in magnetic flux.
  • 5Internal fault in the ABS pump assembly: Damage to the right front wheel speed signal processing circuit inside the ABS control unit, a burnt sampling resistor, or a poor ground connection causes the system to falsely detect a sensor circuit fault.
What To Do
  • 1
    Pre-check and fault confirmation: Connect the VDS or OEM diagnostic tool to read all fault codes. Confirm whether C003504 is a current (Active) or historical (History) fault. Check the freeze frame data and record parameters such as vehicle speed and voltage when the fault occurred. Clear the fault codes and perform a road test to confirm the conditions to reproduce the fault.
  • 2
    Visual and mechanical inspection: Raise the vehicle and check the right front wheel speed sensor installation. Verify the bolt torque (usually 8-12 N·m). Check the sensor head for metal filings, oil contamination, or physical damage. Inspect the signal tone ring integrity and clean its surface. Manually rock the right front wheel to check bearing play and verify no radial or axial looseness.
  • 3
    Electrical parameter measurement: Disconnect the sensor connector and measure the sensor resistance (magnetic inductive type should be 1.0–1.5 kΩ; Hall type requires power for testing). Measure the harness-side supply voltage (should be 12 V ± 0.5 V at ignition ON) and ground wire resistance (<1 Ω). Use an oscilloscope to check the signal waveform. Confirm a sine wave (magnetic inductive type) or square wave (Hall type) with normal amplitude.
  • 4
    Harness continuity and insulation test: Test continuity from the sensor connector to the ABS pump ECU connector (resistance <1Ω). Measure the signal wire insulation resistance to ground and to power (>10MΩ). Inspect the harness securing condition at wear-prone areas, such as the engine compartment right front longitudinal rail and fender liner. Repair damaged sections and install corrugated conduit.
  • 5
    Component replacement and verification: If measurements confirm sensor failure, replace the right front wheel speed sensor with a genuine part (distinguish between magnetic inductive and Hall-effect types; the E5 mostly uses the Hall-effect type). If the bearing has excessive play, replace the wheel hub bearing assembly. After repair, clear the fault code, calibrate the wheel speed sensor (if required), and perform a 5-10 km/h low-speed driving test to confirm synchronization of all four wheel speed signals. Finally, perform an ABS/ESP dynamic road test.
Real-World Cases
BYD DTC AI Analysis

E5: Sensor contamination and connector oxidation caused abnormal signal

✓
A 2018 BYD E5 with 80,000 km had constant ABS and ESP warning lights on the instrument panel. The scan tool read fault code C003504. Technicians removed the right front wheel speed sensor and found the magnetic head coated in iron filings and brake dust. The sensor plug pins showed white oxidation. They cleaned the sensor head and tone ring with carburetor cleaner, sanded the plug pins with fine sandpaper to remove the oxidation, applied conductive grease, and reinstalled. They cleared the fault codes and road tested; the wheel speed signal returned to normal and the warning lights went out. This fault is relatively common in vehicles driven through water or used long-term in humid conditions.
Original source ↗
BYD DTC AI Analysis

Song Pro: Excessive play in right front wheel bearing causing intermittent fault

✓
2019 BYD Song Pro DM, 120,000 km. Dashboard intermittently displayed "Check ESP System". Scan tool showed C003504 as an intermittent fault. Data stream showed right front wheel speed signal occasionally dropping to zero or deviating more than 5 km/h from other wheels. Raised the vehicle and found obvious radial play in the right front wheel bearing (approximately 2 mm), causing the reluctor ring to oscillate radially relative to the sensor during rotation. Replaced the right front hub bearing assembly and readjusted the sensor installation clearance to 0.8 mm. Fault eliminated. Replacing the sensor alone won't fix this type of mechanical wear.
BYD DTC AI Analysis

Wiring harness chafing causes intermittent open circuit in E5 EV

✓
A BYD E5 taxi with 150,000 km on the clock failed to enter READY mode, the instrument cluster displaying a brake system fault. DTC C003504 (current fault) present. Inspection found the RH front wheel speed sensor wiring harness had come loose from its retaining clip at the RH front longitudinal member in the engine bay. The harness had rubbed against the body panel, wearing through the insulation and breaking the copper cores of both internal wires, causing an intermittent open circuit. We stripped back the harness, re-soldered the broken conductors, insulated them with heat-shrink tubing, properly re-routed and secured the harness, and fitted protective corrugated conduit. The vehicle returned to normal after repair, with regenerative braking function restored.
Original source ↗
BYD DTC AI Analysis

Qin EV sensor body aging failure

✓
2018 BYD Qin EV450, 60,000 km. ABS warning light constantly on. Scanned with a diagnostic tool and found DTC C003504—active static fault. Tested the right front wheel speed sensor: power supply normal at 12.4 V, but no pulse signal at the output. Removed the sensor and measured resistance; open circuit (infinite). Internal coil break confirmed. Replaced with an OEM right front wheel speed sensor (part number: 3630420-XXX). Executed the 'sensor calibration' procedure with the scan tool, cleared the codes and road tested. All four wheel speed signals consistent; ABS function restored.
BYD DTC AI Analysis

Tone ring deformed after accident repair, causing signal distortion

✓
A BYD e5 that had undergone right-front collision repairs at a dealership traveled approximately 1,000 km before the ESC warning light illuminated, logging code C003504. Inspection found the replacement right-front steering knuckle assembly (including the signal reluctor ring) installed during the accident repair was slightly deformed, causing reluctor ring radial runout of 0.3 mm (specification <0.1 mm). The sensor detected a signal, but waveform amplitude was unstable, so the ABS pump flagged a circuit fault. Replaced the steering knuckle and hub bearing assembly with a qualified unit, calibrated reluctor ring radial runout to within 0.05 mm using a dial gauge, and cleared the fault.
Other Seal U 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.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.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.
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.