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B1677-00

DTC B1677-00 on BYD new energy vehicles (including DM hybrid and EV models) is a manufacturer-defined fault code — Seal U

Safety System

DTC B1677-00 on BYD new energy vehicles (including DM hybrid and EV models) is a manufacturer-defined fault code.

It denotes a communication fault between the Battery Management System (BMS) and the Motor Control Unit (MCU/VTOG), or a High Voltage Interlock Loop (HVIL) fault, rather than an SRS airbag crash sensor fault.

This fault indicates an open circuit, short circuit, or communication interruption in the high-voltage safety interlock loop.

When the BMS detects a high-voltage safety risk, it triggers a protection mechanism and cuts off the high-voltage power supply, preventing the vehicle from powering on, driving, or charging.

This fault involves high-voltage safety and requires immediate repair.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose high-voltage interlock (HVIL) plug, backed-out terminal, poor connection, or corroded/oxidized pins causing abnormal circuit resistance.
  • 2High-voltage interlock circuit open or short to ground, or wiring harness wear, interference, or water ingress.
  • 3CAN communication wiring harness fault between BMS and MCU (open circuit, short circuit, electromagnetic interference)
  • 4Faulty motor controller (VTOG/MCU) internal CAN communication module or high-voltage interlock detection circuit
  • 5Faulty interlock microswitch inside the high-voltage Power Distribution Unit (PDU), or Manual Service Disconnect (MSD) not fully seated.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (ED400/Launch 431) to read the BMS system fault codes. Confirm B1677-00 and related freeze frame data. Check for accompanying communication fault codes.
  • 2
    Perform a high-voltage interlock loop continuity test: disconnect the low-voltage battery negative terminal, wait 5 minutes, and measure the total resistance of the HVIL circuit using a multimeter. Normal resistance is less than 10Ω. If the resistance is excessive or infinite, sequentially check the interlock pins of each high-voltage component (BMS → service disconnect switch → power battery → PDU → MCU → compressor → PTC).
  • 3
    Check the CAN communication circuit: measure the CAN-H (approx. 2.6V) and CAN-L (approx. 2.4V) voltages at the OBD diagnostic port, check the CAN wiring continuity and terminating resistance (approx. 60Ω) between the BMS and MCU, and rule out open circuits, short circuits, or interference in the wiring.
  • 4
    Visually inspect all high-voltage interlock connectors (orange connectors) for full engagement, backed-out pins, burn marks, corrosion, or water ingress. Focus on wiring harness wear in high-temperature areas of the engine compartment.
  • 5
    If the wiring is normal but the fault persists, swap or replace the suspected controller (MCU, PDU, etc.) to determine if the internal interlock detection circuit or communication module is faulty.
  • 6
    After repairing or replacing the faulty wiring harness/connector, reconnect the low-voltage battery and clear the fault code. Perform a high-voltage system self-check and power-on test, confirm the READY light illuminates normally, and perform a road test to verify.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin DM motor controller high-voltage interlock terminal pin backed out

✓
2015 Qin DM. Dashboard displayed 'Check Power System', EV mode did not work, and the vehicle could not charge. Diagnosis found the BMS reported DTC B1677-00 (communication fault). Testing revealed the high-voltage interlock pin at the motor controller had backed out and deformed, causing an open circuit. Re-crimped the interlock terminal and secured the wiring harness, clearing the fault and restoring high-voltage system operation.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Tang DM PTC water heater interlock connector corrosion

✓
2018 Tang DM suddenly lost power while driving and displayed a powertrain system fault. Read DTC B1677-00 indicating a high-voltage interlock loop fault. Step-by-step inspection traced the fault to internal corrosion and oxidation in the PTC water heater high-voltage interlock connector, causing intermittent circuit resistance. Replacing the PTC high-voltage interlock connector and waterproofing it resolved the issue.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

e5 motor controller: internal CAN module damaged

✓
2016 e5 electric taxi failed to start, READY light off. BMS reported DTC B1677-00 (BMS-VTOG communication fault). Checked external CAN wiring and power supply – normal. Measured termination resistance – normal. Diagnosed as internal CAN communication module failure in the motor controller. Replaced the VTOG controller and flashed the software. Fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Worn CAN wiring harness causing interference – BYD Song Pro DM

✓
A 2019 Song Pro DM suffered intermittent EV mode failure, occurring more frequently in high-temperature conditions. Communication monitoring revealed frame loss between the BMS and MCU. Inspection found the engine bay harness chafing against a body bracket, damaging the CAN-H wire insulation and risking a short to ground. The fault did not recur after repairing the damaged harness and adjusting its routing.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Han EV high voltage distribution box interlock loose connection

✓
A new 2020 Han EV wouldn't start after charging and reported a high voltage system fault. DTC B1677-00 indicated a high voltage interlock abnormality. Found the high voltage distribution box (PDU) interlock connector not fully locked; a loose internal microswitch clip caused a poor connection. Replaced the high voltage distribution box assembly. Fault resolved.
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. Sources: [1]