AU
U0155-00

U0155-00 is a CAN bus communication fault code indicating interrupted data communication between the airbag control unit (SRS ECU) and the instrument cluster — Atto 8

Safety System

U0155-00 is a CAN bus communication fault code indicating interrupted data communication between the airbag control unit (SRS ECU) and the instrument cluster.

In the BYD CAN network architecture, the SRS module transmits airbag status, system fault information, and collision trigger signals in real time to the instrument cluster via the powertrain CAN or body CAN bus.

The SRS sets this fault code if it fails to receive a response message from the instrument cluster within the predetermined cycle (usually 250ms-500ms) or detects a bus physical layer fault.

This fault may prevent the instrument panel from normally illuminating the SRS fault warning lamp and, in extreme cases, affects the safety warning function during a collision.

It classifies as a Level 2 safety-related fault.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Instrument cluster power supply system fault (blown instrument cluster fuse, poor connection in IGN power circuit, open circuit in constant +B power circuit)
  • 2CAN bus physical layer fault (CAN-H to CAN-L short, short to ground or power, open circuit, or excessive contact resistance)
  • 3Poor module ground (loose, oxidized, or corroded instrument cluster or SRS ground point causing increased signal circuit impedance)
  • 4Damaged instrument cluster internal CAN transceiver (electrostatic breakdown or chip aging prevents decoding of bus messages)
  • 5Gateway module routing fault (on some models, the gateway forwards SRS and instrument cluster data; a gateway fault interrupts communication)
What To Do
  • 1
    Use VDS2000 or a dedicated BYD diagnostic tool to perform a full-vehicle DTC scan. Confirm if U0155-00 is the only code present or if other U01XX series communication faults accompany it to determine if it is a single-point fault.
  • 2
    Check the instrument cluster power supply: Measure the voltage at instrument cluster connector terminal 30 (constant +B) and terminal 15 (IGN). Standard value: 12V ± 0.5V. Check the continuity of instrument cluster-related fuses such as FB-02 and FB-22.
  • 3
    Check module ground: Measure the resistance between the instrument cluster GND and body ground, and between the SRS module GND and body ground. Resistance must be less than 1 Ω. Check the tightness of ground point G202 below the left A-pillar of the dashboard.
  • 4
    CAN bus physical layer check: Power off and measure the terminal resistance between OBD diagnostic connector pin 6 (CAN-H) and pin 14 (CAN-L). Standard value: 60 Ω ± 5 Ω. Power on and measure the CAN-H to ground voltage (2.5–3.5 V) and CAN-L to ground voltage (1.5–2.5 V).
  • 5
    Harness continuity test: Disconnect the battery negative terminal, measure the CAN harness continuity between the instrument cluster and the SRS (pin-to-pin resistance should be <1Ω), and check the 20-pin connector behind the instrument panel for backed-out pins or oxidation.
  • 6
    Perform a network sleep/wake test: disconnect the battery negative terminal for more than 5 minutes, reconnect the power, and observe if the fault temporarily disappears to determine if a module crash caused a soft fault.
  • 7
    Module replacement verification: After confirming normal wiring, first swap in an instrument cluster of the same model (prepare for anti-theft matching) to verify if the instrument cluster has an internal CAN transceiver fault.
  • 8
    SRS module programming check: If the fault persists after replacing the instrument cluster, check the SRS module software version. Update the software or replace the SRS control unit if necessary.
Real-World Cases
BYD DTC AI Analysis

Loose instrument panel wiring harness connector causes intermittent U0155 on Qin EV450

✓
A 2018 Qin EV450 had intermittent instrument cluster blackouts and a constant SRS warning light while driving; DTC U0155-00 was intermittent. Inspection found the 20-pin connector behind the instrument cluster had not fully locked. Road vibration caused poor contact on the CAN-H pin, with contact resistance at 12Ω (spec <1Ω). Reinstalled the connector and applied electrical contact protector; the fault has not returned.
BYD DTC AI Analysis

Aftermarket full-LCD instrument cluster modification causes communication protocol mismatch on Tang DM

✓
After the owner installed an aftermarket full LCD instrument cluster, the SRS system continuously logged U0155-00 and the code would not clear. The modified cluster used a non-standard CAN baud rate (250kbps vs factory 500kbps), causing a communication handshake failure with the SRS module. Communication returned to normal after restoring the factory instrument cluster and re-matching the immobilizer.
BYD DTC AI Analysis

Song Pro EV A-Pillar Wiring Harness Corrosion Case After Water Ingress

✓
After driving through water, the dashboard displayed "Please check SRS system". The diagnostic tool read DTC U0155-00. Disassembly revealed the weatherproof grommet below the left A-pillar was damaged. Water had entered the wiring harness connector and caused oxidation; green copper corrosion between the CAN-H and CAN-L pins attenuated the signal. Cleaned the connector with precision electrical contact cleaner, repaired the waterproof seal, and sprayed WD-40 for protection. Fault cleared.
BYD DTC AI Analysis

Qin Pro DM instrument cluster fuse blown with internal short circuit

✓
Vehicle failed to power up with no instrument cluster display. Fault codes included U0155-00 and multiple power supply faults. Inspection found instrument cluster fuse FB-22 blown; the replacement blew immediately. Disassembling the cluster revealed an internal DC-DC converter short. Replaced the cluster with an OEM unit and the instrument panel distribution box. System returned to normal.
BYD DTC AI Analysis

Han EV gateway module failure caused loss of communication between multiple systems

✓
2022 Han EV. Instrument cluster and multimedia both reported communication faults. SRS system stored U0155-00 with additional lost-communication codes for BCM and EPS. CAN bus voltage at the diagnostic port: CAN-H 1.2V, CAN-L 0.8V (abnormal). Disconnected the gateway module (located beneath the center console) and bus voltage returned to normal. Diagnosed as internal CAN transceiver chip failure in the gateway. Replaced the gateway module and performed online coding and configuration; fault resolved.
Other Atto 8 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.