AU
B1655

DTC B1655 indicates a short to ground in the Left Front Impact Sensor signal circuit — Seal U

Safety System

DTC B1655 indicates a short to ground in the Left Front Impact Sensor signal circuit.

In the BYD SRS (Supplemental Restraint System) architecture, this sensor typically mounts on the left front longitudinal beam or bumper reinforcement to detect frontal collision acceleration.

A short to ground means the resistance between the sensor signal wire (usually the positive or communication wire) and the vehicle body ground drops abnormally (<1Ω).

This prevents the SRS control module (ACU) from receiving a valid acceleration signal or causes it to continuously receive a 0V level.

This fault forces the airbag system into fail-safe mode: during a collision, the system may fail to deploy the left front airbag and side curtain airbag, or extreme signal interference could cause unintended deployment.

ISO 26021 classifies this as a Class A passive safety system fault.

Immediately remove the vehicle from service to avoid safety risks.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Front bumper wiring harness wear: Vibration and friction damage the left front crash sensor wiring harness insulation where it passes through the longitudinal beam or bumper bracket, causing direct contact with the metal body and a short to ground.
  • 2Sensor connector water ingress: Poor sealing of the left front sensor connector (usually located in the left front wheel arch or on the inner side of the longitudinal beam) allows water to enter during wading or vehicle washing, causing a short circuit between terminals or a short to ground.
  • 3Internal sensor fault: Damage to the piezoelectric element or integrated circuit inside the crash sensor causes an internal short circuit between the signal output terminal and the ground terminal.
  • 4Post-collision repair defects: Improperly securing the wiring harness during front-end collision repairs allowing sharp metal edges to cut the harness, or incorrect sensor installation pinching the wiring harness.
  • 5Rodent damage: While parked, rodents or other animals chew the motor compartment wiring harness, damaging the left front sensor wiring harness insulation and causing a short to ground.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal. Wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault Confirmation: Use VDS2000 or a dedicated BYD diagnostic tool to read the fault code. Confirm B1655 is a current (Active) code, not a history code. Record the short-circuit resistance value from the freeze frame data.
  • 3
    Visual inspection: Remove the left front bumper assembly. Inspect the left front crash sensor (part number usually starts with 69C) for deformation. Check the connector for looseness, water ingress, or signs of corrosion.
  • 4
    Circuit measurement: Disconnect the sensor connector. Use a multimeter to measure the resistance to ground at the harness-side signal terminal (usually the yellow/black wire). Normal resistance is >10 MΩ; a reading <5 Ω confirms a short to ground. Also measure the resistance between the sensor body terminals. Normal resistance is 2-3 kΩ (refer to the repair manual for specific values).
  • 5
    Wiring harness inspection: Inspect the harness routing along the left front longitudinal rail. Focus on harness retaining clips and sheet metal pass-through holes (remove the left front wheel arch liner). Check for insulation damage. Use an oscilloscope to verify if the SRS communication waveform (typically a PWM signal) pulls low.
  • 6
    Repair or replace: If the wiring harness is damaged, repair it using heat-shrink tubing and waterproof tape. Ensure insulation resistance is >10MΩ. If the sensor has an internal short circuit, replace the left front crash sensor (Note: BYD sensor part numbers vary by model; Yuan, Song, and Qin series sensors are generally not interchangeable).
  • 7
    System verification: Reconnect all components, turn on the power, use the diagnostic tool to clear the fault code, and perform the 'SRS system self-test' (usually requires cycling the ignition switch ON-OFF 3 times). Confirm B1655 does not reappear and the system generates no new fault codes.
  • 8
    Calibration and road test: Some models (such as Tang DM-p) require collision sensor zero-point calibration on a level road surface. Finally, perform a 5km road test to confirm the airbag warning light remains off.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song MAX B1655 fault after water wading

✓
After driving through floodwater in heavy rain, the airbag warning light on a 2019 Song MAX DM stayed on constantly. Read fault code B1655. Found the drain hole under the left front side member blocked. Accumulated water entered the left front impact sensor connector (behind the left front wheel arch liner) and caused corrosion. Cleared the drain hole, cleaned the connector terminals with electronic contact cleaner, applied conductive grease, and replaced the waterproof seal. After clearing the fault, performed SRS system initialisation.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Tang EV sensor short circuit after accident repair

✓
2021 Tang EV had the front bumper replaced at the dealership following a front-end collision. The airbag warning light illuminated the day after vehicle collection. Diagnosis revealed current fault code B1655. Inspection found the left front impact sensor wiring harness had not been properly secured during the accident repair; the sharp metal edge of the bumper bracket had cut through the harness, causing a short to ground. Repaired the wiring and re-secured it using OEM cable clips, adjusting the routing to avoid contact with sharp edges. Lesson: Accident repairs must strictly follow the body repair manual wiring layout diagrams.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Yuan EV sensor internal fault

✓
2019 BYD Yuan EV airbag warning light came on while driving, no collision history. Retrieved DTC B1655. Measured signal wire to ground resistance at the sensor connector: 0.3 Ω (abnormal). After disconnecting the sensor, harness-side resistance returned to normal (infinity), confirming an internal sensor short. Replaced the left front impact sensor (Part No.: 69C-4123011) — fault resolved. Teardown of the old part revealed a capacitor solder joint on the internal PCB had detached from long-term vibration, shorting the signal wire to ground.
BYD DTC AI AnalysisFrom Chinese market (translated)

Rodent damage to wiring harness on BYD Qin Pro

✓
2020 Qin Pro threw DTC B1655 after being parked for a week. Inspection found rodents had chewed through the wiring harness protective sleeve at the left-front corner of the engine bay. The left front impact sensor signal wire insulation was damaged and shorting to ground on the longitudinal beam. Repair: Repaired the damaged harness (3 wires), re-wrapped it with rodent-deterrent tape (capsaicin-coated), and installed an ultrasonic rodent repeller nearby. Advised the customer to close off rodent access routes near the bonnet seal when parking.
BYD DTC AI AnalysisFrom Chinese market (translated)

Aftermarket modifications caused SRS fault in Tang DM

✓
A 2021 Tang DM owner accidentally drilled through the left front SRS wiring harness while retrofitting a front radar, when drilling into the left front side member to mount a bracket, triggering DTC B1655. As the damage affected the main harness trunk, we replaced the entire left front SRS wiring harness assembly (part number: 69C-4123015) per factory repair standards, rather than splicing, to ensure signal integrity during a collision. Warning: Never drill or weld in the front side member area without authorization; this involves SRS wiring safety.
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]