AU
B1655-00

DTC B1655-00 indicates the airbag control unit (SRS ECU) detects an abnormally low-resistance path (typically <10Ω) between the left front impact sensor (FIS) signal circuit and body ground — Seal U

Safety System

DTC B1655-00 indicates the airbag control unit (SRS ECU) detects an abnormally low-resistance path (typically <10Ω) between the left front impact sensor (FIS) signal circuit and body ground.

In the BYD SRS architecture, this sensor is typically a piezoelectric acceleration sensor.

It communicates with the SRS ECU via a shielded twisted-pair wire and operates on a 2.5V reference bias voltage.

A short to ground causes the ECU to continuously receive a 0V low-level signal, potentially causing the following: 1) the system misinterprets the condition as a sensor fault, enters fail-safe mode, and disables airbag deployment; 2) in extreme cases, intermittent changes in short-circuit resistance may cause unintended airbag deployment.

This is a hard-wire fault, not a communication fault.

It directly affects the trigger logic for the driver front airbag and seat belt pretensioner.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Damaged wiring harness insulation in the left front longitudinal beam area: The sensor wiring harness routes along the left front longitudinal beam. Flying road debris or underbody bottoming out can wear through the outer sheath, causing the copper core to contact the vehicle body metal and create a short to ground.
  • 2Connector seal failure causing water ingress: The sensor connector is located near the front wheel arch or side member. Aging sealing rings allow water to enter during wading or high-pressure washing. Electrolytes in the water cause a short circuit between pins or to ground.
  • 3Internal sensor circuit breakdown: A voltage surge (such as incorrect battery connection or welding without disconnecting the wiring harness) breaks down the crash sensor's internal capacitor or Zener diode, causing an internal short circuit between the power supply pin and the ground pin.
  • 4Post-accident repair defects: Sharp body panel edges or retaining clips pinch the wiring harness after a front-end collision. Long-term vibration cuts through the insulation, creating a hidden short to ground.
  • 5Rodent damage: Rodents in the parking area gnaw the wiring harness, causing exposed wires to contact the vehicle body ground.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Connect the VDS or Launch diagnostic tool to read freeze frame data. Record the vehicle speed and ambient temperature when the fault occurred. Clear the fault code, then perform an SRS self-check to confirm if B1655-00 is a Current Code.
  • 3
    Visual inspection: Remove the left front bumper cover. Inspect the left front crash sensor (located at the front of the left front longitudinal beam or headlamp bracket) for physical damage. Inspect connectors G36 and C35 for looseness, water ingress, or green corrosion.
  • 4
    Circuit continuity test: Disconnect the SRS ECU and sensor connectors. Use a multimeter to measure the continuity resistance from G36-33 (L/W wire) to terminal C35-2. Resistance must be <1 Ω. Measure the continuity resistance from G36-34 (Br/W wire) to terminal C35-1. Resistance must be <1 Ω.
  • 5
    Insulation-to-ground test: With the connector disconnected, measure the resistance from sensor-side pins C35-1 and C35-2 to body ground. Normal resistance is infinite (>10MΩ). If continuity exists, inspect the wiring harness along its routing for abrasion or damaged insulation at the fixing points on the left front longitudinal beam and fender liner.
  • 6
    Sensor swap verification: Swap the left front and right front crash sensors. If the fault code follows the sensor to B1656-00 (right front sensor short to ground), the sensor has an internal fault. If the fault code remains B1655-00, the wiring harness is faulty.
  • 7
    Repair and Verification: Repair the damaged wiring harness (use heat-shrink tubing for waterproofing) or replace the sensor. Restore the connection and reconnect the battery. Use the diagnostic tool to execute 'SRS System Configuration' and 'Crash Sensor Zero-Point Calibration'. Finally, perform a road test to verify the repair.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Left front impact sensor connector shorted after wading

✓
A 2018 BYD Qin EV450 had the SRS warning light on the instrument panel stay on after driving through heavy flood water. The diagnostic scanner read active fault code B1655-00. Removing the left front bumper revealed obvious water traces inside the left front impact sensor connector G36. Green oxidation was present between pin 3 (Blue/White wire) and pin 4 (Brown/White wire), with pin 3 showing 0.3Ω resistance to ground. The connector seal had aged, allowing moisture ingress during the flood and causing a short to ground. Repair: Cleaned the connector with electronic contact cleaner, blow-dried it, applied conductive anti-corrosion grease, and fitted a new waterproof seal. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Chafed wiring harness causing hidden short circuit after accident repair

✓
A 2017 model Qin 100 developed an intermittent SRS warning light three months after front collision repairs, and the scan tool showed history code B1655-00. While the sensor body tested normal, measuring the wiring harness revealed that the C35-2 (L/W wire) resistance to ground jumped from infinity to 5Ω when the harness was flexed. Removing the left front frame rail inner trim panel revealed that during the accident repair, the wiring harness had been secured under a clip on the sharp edge of the rail. Long-term vibration had cut through the insulation, allowing the copper core to intermittently ground against the body. The repair involved re-wrapping the harness with double-layer protection (fleece tape and PVC tape), rerouting the harness away from sharp edges, and relocating the fixing clips, permanently resolving the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal sensor circuit breakdown caused a hard short.

✓
A 2019 BYD E1 came in with the SRS warning light on after body welding. The light was on at startup. We retrieved DTC B1655-00. The sensor harness resistance to ground was normal. Swapping the left and right sensors moved the fault to the right side (B1656-00), confirming an internal sensor fault. We disassembled the faulty sensor and found filter capacitor C1 on the internal PCB had shorted, shorting the signal line to ground. Root cause: the battery negative terminal was not disconnected during welding; welding current fed back through the sensor harness and broke down the component. We replaced the left front impact sensor (P/N BYD-10620201), then re-welded, strictly following the power-off procedure. Fault resolved.
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]