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U0155

U0155 is an ISO 15031 CAN bus communication fault code — Seal U

Safety System

U0155 is an ISO 15031 CAN bus communication fault code.

It indicates a CAN communication interruption between the SRS airbag system (or other vehicle control units) and the instrument cluster control unit (IPC/ICU).

In BYD New Energy Vehicles (NEVs), the instrument cluster displays vehicle speed and battery level, and also shows airbag status, fault warning lamps, and seat belt reminders.

This fault means the SRS module fails to receive a response message from the instrument cluster within 500ms, or the message checksum fails.

A physical layer fault in the Powertrain CAN or Body CAN bus can cause this issue, resulting in a blank instrument cluster display, a continuously illuminated airbag warning lamp, and an abnormal odometer display.

In extreme cases, this fault affects normal airbag deployment logic during a collision because the system cannot confirm the instrument cluster warning lamp status.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Instrument cluster control unit power supply circuit fault (blown fuse, open IGN power circuit) or poor ground connection (loose G201/G202 ground points), preventing normal instrument cluster operation.
  • 2CAN bus physical layer fault: CAN-H to CAN-L short circuit, short to ground/power, or wiring open circuit (common at dashboard wiring harness bends or terminal back-out at A-pillar connectors X202/X203).
  • 3The instrument cluster internal CAN transceiver (TJA1043 or compatible chip) is faulty, or the main control MCU crashed and cannot respond to bus requests.
  • 4Gateway controller fault: In models using a multi-network architecture (such as Tang and Qin), the gateway routes messages between the SRS and the instrument cluster. Gateway failure disrupts communication across network segments.
  • 5Mismatched software versions in related control units or a program crash causes message ID conflicts or checksum errors, triggering a communication timeout.
What To Do
  • 1
    Use the VDS or ED400 diagnostic tool to read all DTCs. Confirm if U0155 is a current or history fault, and record the freeze frame data (vehicle speed, voltage, etc. at the time of occurrence). Check for accompanying U01xx series communication fault codes (such as loss of communication with the BMS or ABS) to determine if this is an isolated instrument cluster fault or a bus failure.
  • 2
    Visually inspect the instrument cluster display for a black, distorted, or frozen screen. Check the instrument panel fuses (F1/14, F2/11, etc., depending on the model). Measure the voltage at pin 1 (B+ constant power) and pin 2 (IGN power) of instrument cluster connector X101, and measure the resistance at the ground pin. Verify the power supply is ≥12V (or ≥12V for the low-voltage system on high-voltage models) and the ground resistance is <1Ω.
  • 3
    Disconnect the battery negative terminal, wait 5 minutes, and measure the resistance between pins 6 (CAN-H) and 14 (CAN-L) at the diagnostic connector (OBD). Normal resistance is approximately 60 Ω (two 120 Ω terminating resistors in parallel). If the resistance is abnormal (0 Ω short circuit or ∞ open circuit), inspect the instrument cluster CAN wiring section by section. Standard CAN-H voltage is 2.6-3.5 V, and standard CAN-L voltage is 1.5-2.4 V. Use an oscilloscope to check for waveform distortion.
  • 4
    Inspect the instrument panel wiring harness connectors (especially X202, X203, and GJ201) for backed-out pins, oxidation, or water corrosion. Check the main wiring harness behind the instrument cluster near the steering column for wear. Repair any damaged harness insulation.
  • 5
    If the wiring is normal, reset the instrument cluster control unit power (disconnect power for more than 30 seconds). If the fault persists, check the SRS module and instrument cluster software versions, and update to the latest versions if necessary. If the issue remains, perform a swap test: install the suspected instrument cluster into a known good vehicle with the same configuration to verify, or install a test instrument cluster.
  • 6
    After repair, clear the fault code, perform a road test and monitor the data stream: verify 'Instrument Communication Status' in the SRS module displays 'Normal', and confirm all instrument cluster warning lights self-test normally with no abnormal illumination.
Real-World Cases
BYD DTC AI Analysis

BYD F6 Instrument Cluster Intermittent Communication Failure (Window Regulator Interference Case)

✓
A BYD F6 experienced intermittent instrument cluster blackouts while driving. The SRS system set U0155, sometimes accompanied by U1102 and U0199. The technician suspected CAN bus interference. The left front door window switch was a non-genuine part lacking shielding; its internal circuitry generated high-frequency interference pulses that coupled onto the instrument cluster CAN lines. Replacing the switch with a genuine unit with shielding restored normal CAN waveforms and cleared U0155. Non-genuine accessories can disrupt instrument cluster communication via CAN bus interference.
Original source ↗
BYD DTC AI Analysis

BYD Qin BMS and instrument cluster communication loss

✓
BYD Qin DM. The instrument cluster displayed “Check SRS System”. The scan tool read U0155 from the BMS (Battery Management System). Per the workshop manual, the BMS transmits SOC and fault status to the cluster via the CAN bus. Inspection found pin 20 (CAN-L) of harness connector X201 behind the cluster had backed out, interrupting BMS-to-cluster communication. Reseating the pin and applying conductive paste restored communication between the BMS and cluster; the DTC cleared.
Original source ↗
BYD DTC AI Analysis

BYD ABS/ESP system U0155 communication fault (brake system related)

✓
A BYD SUV logged DTC U0155-00 (Lost Communication with BCM/Instrument Cluster) in the ABS/ESP system, with the ABS and airbag warning lights staying on. Testing found the Gateway controller's internal CAN transceiver had failed, blocking message routing between the chassis CAN and body CAN and cutting off ABS module communication with the instrument cluster. Replaced the Gateway controller and configured the parameters. Cross-network communication returned to normal and the fault codes cleared.
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.