AU
B17A500

This fault code typically indicates a circuit fault in the left electronic parking brake (EPB) actuator (passenger side) — Seal U

Safety System

This fault code typically indicates a circuit fault in the left electronic parking brake (EPB) actuator (passenger side).

Associated issues include motor damage, abnormal control wiring, or module drive circuit faults.

Some documentation labels this code as an SRS 'passenger-side side collision' record.

However, field cases on BYD Qin, Han, Song, and Tang models confirm B17A500 indicates an open circuit, short circuit, or current overload in the left EPB motor drive circuit.

This fault disables the electronic parking brake (unable to apply or release) and triggers a 'Please check the electronic parking system' instrument cluster warning.

Extreme cases cause rear brake drag, increased driving resistance, or parking failure, posing a severe safety hazard.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Excessive wear or an open circuit in the carbon brushes of the left EPB actuator internal DC motor causes abnormal resistance (normal: 1.0-2.5 Ω; fault: infinite).
  • 2Enlarged, loose, oxidized, or corroded harness connector terminals, commonly at the body-to-floor harness connector, or poor contact at ground point G106 below the left A-pillar.
  • 3Vehicle wading or seal failure causes water ingress into the actuator or connector, resulting in a short to ground or motor rust and seizure.
  • 4Improper repair procedures (e.g., forcing the piston back without entering service mode during brake pad replacement) causing motor overload, reduction gear tooth breakage, or leadscrew deformation.
  • 5Lost EPB control module software calibration or a damaged hardware drive circuit causes abnormal current/voltage output to the left actuator.
What To Do
  • 1
    Use the VDS diagnostic tool to read the complete fault codes and freeze frame data. Confirm whether B17A500 is a current or history fault. Check the data stream for the left actuator operating current (normal peak <15A) and the position sensor signal.
  • 2
    Raise the vehicle and visually inspect the left EPB actuator and electrical connector. Check for obvious signs of water ingress, burn marks, or impact damage. Verify the mechanical connection is free from binding.
  • 3
    Disconnect the left actuator electrical connector and use a multimeter to measure the resistance between the two motor terminals (standard value: 1.0-2.5 Ω). If the resistance is infinite or too high, the actuator has an internal open circuit. Replace the assembly.
  • 4
    If actuator resistance is normal, measure the continuity of the power supply wire, ground wire, and CAN communication wires from the EPB control module (usually below the left A-pillar) to the actuator connector. Inspect the rear panel wiring harness mating connector and ground point G106. Repair any loose connections, enlarged terminals, or oxidation. If necessary, use a dedicated terminal release tool to restore terminal retention force.
  • 5
    If the actuator is faulty, use VDS to enter 'Brake System Maintenance Mode' before replacement to fully release the motor lead screw pressure and prevent forced removal. Exit Maintenance Mode after installing the new actuator.
  • 6
    Perform EPB system initialization and calibration: Use the VDS to run the 'Write Zero Position' or 'Self-learning' procedure. This usually requires operating the electronic parking brake switch multiple times (pull up and release 3-5 times) until the module stores the limit positions.
  • 7
    Clear all fault codes and perform a road test. Test the apply/release function while stationary, Auto Vehicle Hold (AVH) activation and release while driving, Hill Start Assist, and other functions. Monitor the data stream to confirm the actuator current on both sides is symmetrical and shows no abnormal fluctuations.
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i left actuator motor internal open circuit

✓
Symptoms: 2021 Song PLUS DM-i. After parking and engaging the electronic parking brake, the dashboard displayed "Check Electronic Parking System", the yellow warning lamp stayed on, and Auto Hold failed. Fault intermittently cleared after restarting. VDS retrieved DTC B17A500 (Left Actuator Circuit Fault) accompanied by C100316. Diagnosis: Lifted the vehicle; no water ingress in connectors. Measured infinite resistance (open circuit) across the left EPB actuator motor; wiring harness continuity normal. Disassembly revealed worn internal motor carbon brushes causing the open circuit. Fix: Replaced the left electronic parking brake actuator assembly (Part No.: 6A-3502010). Performed EPB system calibration using VDS (writing zero position). Fault cleared.
BYD DTC AI Analysis

Han EV ground point oxidation and wiring harness loose connection

✓
Symptoms: 2020 Han EV Long Range intermittently reports electronic parking brake fault on cold start; fault clears after warm-up and occurs more frequently as ambient temperature drops. Scan tool showed historic DTC B17A500; live data indicated left actuator current intermittently at 0A. Diagnosis: Measured EPB control module supply voltage at 11.8V (low). Inspected ground point G106 inside the left front sill: screw was oxidized and loose, with contact resistance of 3.2Ω. After cleaning and tightening the ground point, voltage recovered to 12.4V, but the cold-start fault persisted. Further inspection found expanded pin sockets at the EPB main harness connector (body-to-floor harness junction). Resolution: Cleaned and tightened G106 ground point and applied conductive paste. Used a dedicated terminal release tool to repair the expanded connector sockets, increasing pin retention force. Applied waterproof silicone sealant at the connector to prevent oxidation. Fault cleared.
BYD DTC AI Analysis

Qin Pro DM motor seized after improper brake pad replacement

✓
**Symptoms:** After a non-4S shop replaced the rear brake pads on a 2019 Qin Pro DM, the dashboard displayed "Electronic Parking System Fault" with code B17A500. The electronic parking brake would not release and the rear wheels locked up. **Diagnosis:** The technician failed to use a diagnostic tool to enter "Service Mode" during replacement, instead forcibly pressing the caliper piston back and overloading the motor. Live data showed the left actuator motor current reached 28A (normal peak <15A), indicating internal gear seizure or lead screw deformation. Disassembly revealed shattered teeth on the internal reduction gear set and a seized motor rotor. **Resolution:** Replaced the left EPB actuator assembly. Used VDS to enter "Brake System Service Mode" and properly replaced the right brake pads. Exited service mode and performed EPB initialization (completed self-learning through multiple apply/release cycles of the parking brake).
BYD DTC AI Analysis

Tang DM-i actuator shorted due to water ingress after wading

✓
Symptoms: The 2021 Tang DM-i waded through approximately 30 cm of water. The dashboard then showed an electronic parking brake fault, DTCs B17A500 and B17A600 (right side) appeared simultaneously, and the electronic handbrake failed completely. Diagnosis: Inspected the rear wheel actuators and found mud and water in the left actuator connector. Measured resistance between pins 1-2 of the left actuator connector and ground: found a short (should be insulated). Traced the rear wiring harness and found poor sealing on the left rear panel harness from prior accident repairs; the corrugated conduit had damage that let water in. Cleaning the connector cleared the short, but water had rusted the actuator internals, increasing mechanical resistance. Resolution: Replaced both left and right EPB actuators (replace in pairs after wading). Repaired the rear panel harness corrugated conduit with heat-shrink tubing and waterproof tape for a double seal. Packed the connector with silicone grease to prevent water ingress.
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.