AU
C059900

This fault code indicates the EPB (Electronic Parking Brake) control module detects an uncalibrated system, a communication fault, or an actuator fault — Seal U

Braking System

This fault code indicates the EPB (Electronic Parking Brake) control module detects an uncalibrated system, a communication fault, or an actuator fault.

Although some repair data categorizes this code under the IPB (Integrated Power Brake) system, C059900 typically indicates interrupted CAN communication between the EPB control unit and the left and right rear parking motors, an unstable power supply, or lost internal module calibration data.

When this fault occurs, the EPB control module cannot accurately acquire motor position signals or execute control commands, causing partial or complete electronic parking brake failure.

Symptoms include the inability to release or apply the parking brake, and instrument cluster warnings.

Extreme cases compromise driving safety.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Poor contact in the EPB control module power supply/ground circuit, especially oxidized or loose ground points G106/G107, or low battery voltage (static <12V).
  • 2Open or short circuit in the left or right rear wheel EPB actuator motor wiring harness. Long-term bending at the door hinge or chassis pass-through commonly breaks the internal copper strands (outer insulation remains intact).
  • 3Internal circuit board corrosion, chip damage, or loss of software calibration data in the EPB control module, typically due to water ingress or voltage fluctuations.
  • 4Internal mechanical binding in the rear parking brake motor or wear in the worm gear mechanism causes abnormal motor current (>20A) and triggers overheat protection.
  • 5CAN network communication fault: Communication timeout between the EPB module and the Vehicle Control Unit (VCU) or IPB module.
What To Do
  • 1
    Use the VDS2000/3000 diagnostic tool to read the complete fault codes. Check for accompanying sub-codes such as C059801 (right rear wheel fault) and C059802 (left rear wheel fault). View the motor current, position, and switch status in the data stream.
  • 2
    Check battery health. Measure static voltage (should be ≥12V) and voltage after startup (13.8-14.5V). Check the EPB control module ground point (usually G106 on the left side of the dashboard or under the center tunnel) for proper tightening torque and oxidation.
  • 3
    Remove and inspect the EPB control module (located under the center armrest, behind the gear selector mechanism). Check the housing seal and inspect the internal circuit board for signs of water ingress or corrosion. Measure the voltage at the module power supply pins.
  • 4
    Inspect the left and right rear wheel EPB motor wiring harnesses for wear, focusing on the door hinges and chassis pass-throughs. Use a multimeter to measure motor resistance (normal value approx. 2-4 Ω) and harness continuity.
  • 5
    If the wiring harness and motor are normal, replace the EPB control module. Perform module matching and programming (enter the VIN, tire specifications, and vehicle configuration parameters), and execute the motor bedding-in procedure (perform 5 apply-release cycles for each of the left and right wheels).
  • 6
    If replacing the motor or cable, adjust the cable preload (Standard: 1-2 mm cable free play after installation) and perform EPB initialization learning: Ignition switch ON → Press and hold the brake pedal → Pull up the EPB switch for 5 seconds → Release the switch → Wait 10 seconds to complete self-learning. Finally, perform a road test to verify.
Real-World Cases
BYD DTC AI Analysis

Wiring harness break caused EPB failure in BYD Qin Pro EV

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Symptoms: After starting the vehicle, the instrument cluster displayed "Check Electronic Parking Brake System". The EPB switch failed completely, the parking brake would not release, and the vehicle was immobilised. Diagnosis: VDS retrieved DTC C059900 along with C059801. The EPB module had normal power and earth. Found internal wire fracture in the right rear EPB motor harness at the right rear door hinge (outer insulation intact), cutting power to the motor. Repair: Cut out the damaged harness section, resoldered the wires, and fitted waterproof insulation sleeving. Rerouted the harness to avoid interference. Cleared the codes and performed EPB initialisation. Function restored.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro DM — Low battery voltage triggered system protection

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Symptoms: Electronic parking brake warning light occasionally illuminates while driving. Intermittent no-start after parking, more common on cold starts. DTC C059900 stored. Diagnosis: Measured static battery voltage at only 11.2V (capacity degraded to 60%). Inspected EPB control module ground point G106 and found loose bolt with oxidised contact surface, causing voltage instability that triggered protection. Solution: Replaced the degraded battery. Removed ground point G106, sanded off the oxidation, applied conductive paste, and tightened to specified torque (8–10 N·m). Cleared fault codes and road-tested one week without recurrence.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM control module internal fault

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Symptoms: While driving at high speed, the instrument cluster suddenly displayed "Electronic Parking System Fault". The vehicle continued to drive normally, but after stopping, the electronic parking brake function failed completely with no response from the switch. Diagnosis: Retrieved DTC C059900 which could not be cleared. Inspected the EPB control module (located beneath the centre console) and found cracks in the housing. Disassembly revealed water ingress had corroded the internal circuit board and shorted the integrated circuits. Resolution: Replaced the electronic parking brake control module with a new unit (part number: 3H-3600100). Performed EPB system matching with a diagnostic scan tool (entering the VIN and tyre specification parameters). Executed the motor bedding-in procedure (5 tighten-release cycles for each wheel).
Original source ↗
BYD DTC AI Analysis

BYD Han EV rear parking brake motor jammed

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Symptoms: EPB warning triggered when parking. Left rear wheel made clicking noise. Parking brake failed to release fully. Vehicle dragged when driving. DTC C059900 displayed. Diagnosis: Lifted vehicle. Left rear EPB motor ran with abnormal noise but brake caliper did not move. Removed motor and applied direct power: motor spun but output shaft had no torque. Internal worm gear worn and jammed. Data stream showed left rear motor current consistently above 20A (normal <8A), triggering overheat protection. Resolution: Replaced left rear EPB motor assembly (motor and cable). Adjusted cable preload during installation (free play 1–2mm). Performed EPB initialization after replacement: ignition ON → depress brake pedal → pull and hold EPB switch for 5 seconds → release switch → wait 10 seconds for self-learning.
Original source ↗
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.