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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 — Atto 3

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 — Atto 3
  • 1Loose high-voltage interlock (HVIL) plug, backed-out terminal, poor connection, or corroded/oxidized pins causing abnormal circuit resistance.
  • 2Open circuit, short to ground, harness wear, interference, or water ingress in the high-voltage interlock loop wiring.
  • 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.
  • 5High-voltage Power Distribution Unit (PDU) internal interlock microswitch fault or Manual Service Disconnect (MSD) not fully seated.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (ED400/Launch X-431) to read 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. The resistance must be less than 10Ω. If the resistance is excessive or infinite, inspect the interlock pins of each high-voltage component section by section (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 between the BMS and MCU, and measure the terminating resistance (approx. 60Ω). Eliminate any open circuits, short circuits, or interference.
  • 4
    Visually inspect all high-voltage interlock connectors (orange connectors) to verify they are fully locked and free of backed-out pins, burn marks, corrosion, or water ingress. Focus on wiring harness wear in high-temperature areas of the motor compartment.
  • 5
    If 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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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]