AU
B17A800

The BYD SRS (airbag system) control unit logs diagnostic trouble code (DTC) B17A800 to indicate interrupted communication or a physical layer connection fault between the airbag control module and the vehicle CAN bus network — Atto 8

Safety System

The BYD SRS (airbag system) control unit logs diagnostic trouble code (DTC) B17A800 to indicate interrupted communication or a physical layer connection fault between the airbag control module and the vehicle CAN bus network.

In models such as the BYD Qin PRO, the SRS ECU exchanges real-time data with the vehicle control unit (VCU), body control module (BCM), instrument cluster, and gateway via the CAN bus (typically the powertrain CAN or chassis CAN, depending on the configuration).

The ECU transmits critical safety data, including crash signals, airbag status, fault information, and system readiness status.

The SRS ECU sets this fault code when it continuously detects abnormal voltage on the CAN_H and CAN_L lines (recessive level outside the normal 2.0-3.0 V range, or abnormal dominant level), bus termination resistance deviating from the standard 60 Ω value (after parallel connection), or no valid data frame received within the specified time limit (usually 250 ms-500 ms).

This functional safety fault may prevent proper airbag deployment and seat belt pretensioner operation during a collision.

It also disables the collision-triggered automatic unlocking and high-voltage cut-off functions.

As a result, the instrument panel airbag warning lamp remains illuminated and the vehicle enters safety protection mode.

The B17A800 fault code on the Atto 8 indicates a communication fault between the SRS airbag control unit and the vehicle CAN bus. Severity is medium, as it may affect airbag, seat belt pretensioner, crash unlock, and high-voltage cut-off functions. Common causes include damaged CAN wiring or loose/corroded SRS ECU connectors, and faulty bus termination or ECU transceiver issues. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from 5 recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Physical damage to the CAN bus wiring harness: After an accident, water ingress, or prolonged vibration, the CAN_H (orange/black) or CAN_L (orange/brown) wires in the front compartment or chassis harness develop an open circuit, short to ground, or short to power. Connectors oxidize or loosen. Specifically, the SRS ECU connector (usually located at the center tunnel or bulkhead) has backed-out or corroded pins.
  • 2Abnormal terminal resistance: Internal damage to the 120Ω terminating resistors at both ends of the CAN bus (located in the gateway or instrument cluster) causes a bus impedance mismatch, or an internal transceiver fault in the SRS ECU causes an abnormal bus load, resulting in signal reflection and communication interruption.
  • 3Power supply fault: Poor contact at the SRS ECU constant power (B+), ignition switch power (IG1), or ground wire (GND), or voltage below 9V or above 16V, causing control unit reset or unstable CAN transceiver power supply.
  • 4Electromagnetic interference or module fault: Installed aftermarket electronic equipment (dash cams, navigation systems, etc.) interferes with the CAN signal; or a damaged internal CAN transceiver in an adjacent module (such as ABS or ESP) pulls down the bus level, causing an SRS communication failure.
  • 5SRS control unit internal fault: ECU internal CAN driver chip (such as TJA1040/1051) breakdown, crystal oscillator stall, or software crash, typically setting a hard fault code that will not clear.
What To Do
  • 1
    Initial inspection and fault confirmation: Use the BYD dedicated diagnostic tool (ED400/VDS) to read all fault codes. Verify B17A800 is a Current code, not a History code. Check the instrument cluster airbag warning light status. Determine if the vehicle experienced a collision or water ingress. Inspect the front compartment and center tunnel wiring harnesses for damage, modifications, or signs of water ingress.
  • 2
    CAN bus physical layer check: Disconnect the battery negative terminal, wait 3 minutes, and measure the resistance between pins 6 (CAN_H) and 14 (CAN_L) of the diagnostic connector (OBD). Normal resistance is approximately 60 Ω (two 120 Ω terminating resistors in parallel). A reading of 120 Ω indicates an open circuit in one terminating resistor or the wiring. A reading of 0 Ω indicates a short circuit in the wiring. Measure the resistance from CAN_H to ground and power, and from CAN_L to ground and power. All readings must exceed 1 MΩ.
  • 3
    SRS module specific inspection: Locate the SRS ECU (usually under the center console or inside the center armrest box on the Qin PRO). Inspect the wiring harness connector (usually 24-32 pins) for oxidation or looseness. Test the CAN waveform using an oscilloscope. A normal waveform shows a 2.5V reference, with CAN_H at 3.5V dominant / 2.5V recessive, and CAN_L at 1.5V dominant / 2.5V recessive. If the waveform is distorted or flat and the bus returns to normal after unplugging the SRS connector, this indicates an internal SRS ECU fault.
  • 4
    Segmented isolation troubleshooting: Use the node disconnection method. Sequentially disconnect the ABS, ESP, BCM, and other modules. After disconnecting each module, measure the bus resistance and attempt to clear the fault code to identify the module causing the bus failure. Focus inspection on the gateway controller (integrated into the BCM or a standalone gateway on the Qin PRO), as it forwards signals between network segments.
  • 5
    Repair and verification: Repair open or shorted wiring (replace the wiring harness or solder), clean oxidized connectors, and replace the SRS ECU or faulty module if necessary. After repair, clear the fault code, perform a road test, monitor the CAN communication data stream, and confirm the SRS status is 'normal' and the airbag warning lamp is off. Perform an airbag system function test (use a simulated resistor; never test with a real airbag) and verify the crash signal transmits normally to the VCU to trigger the high-voltage interlock.
Real-World Cases
BYD DTC AI Analysis

Qin PRO DM: CAN bus corrosion after water ingress caused SRS communication interruption

✓
A 2019 Qin Pro DM logged a B17A800 fault code and the airbag warning lamp stayed on constantly after driving through heavy floodwater. Inspection found water had reached the door sills and flooded the center tunnel. Removing the SRS ECU from the center armrest revealed severe green oxidation on pins 15 (CAN_H) and 16 (CAN_L) of its 32-pin connector, plus water in the harness-side plug. The CAN lines measured infinite resistance (open circuit). Fix: Cleaned the connector with precision electrical contact cleaner, baked the harness to remove internal moisture, replaced the SRS ECU connector terminals, and resealed the connector. After repair, bus resistance returned to 60Ω, the fault cleared, and SRS communication normalized. Inspect the sunroof drain hoses and floor seals to prevent recurrence.
BYD DTC AI Analysis

Aftermarket dash cam causing CAN bus signal interference

✓
2018 BYD Qin Pro (petrol). Owner fitted an aftermarket 360-degree camera; dashboard displayed "Check SRS System". Read DTC B17A800. The installer had tapped the recorder power into the OBD port CAN lines without shielding. Removing the modified wiring did not clear the fault; CAN waveforms showed heavy noise. The recorder's CAN decoder (reading vehicle speed) was spliced into the Powertrain CAN in parallel without termination resistor, causing bus impedance mismatch. Removed the non-genuine decoder and restored the factory harness. Measured 60Ω at the SRS ECU connector. Cleared the codes; vehicle returned to normal. Do not splice unauthorised devices into BYD CAN buses.
BYD DTC AI Analysis

SRS ECU internal transceiver chip damaged

✓
2019 Qin PRO with 80,000 km, no accident or modification history. Intermittent airbag warning light. Scanner read code B17A800. Code cleared but returned while driving. Measured CAN line voltage and resistance—both normal. Waveform check revealed abnormal pulses. Substitution test: swapped SRS ECU with unit from an identical known-good vehicle; fault transferred. Teardown of the faulty ECU revealed the internal NXP TJA1042 CAN transceiver chip had overheated and burned, with surrounding capacitors leaking. Root cause: ECU operated in a high-temperature environment (poor central tunnel heat dissipation), causing chip aging. Replaced SRS ECU with a new unit (requires online programming to match the VIN and immobilizer information), updated SRS software to the latest version (optimizes CAN fault tolerance mechanisms). Fault completely resolved.
BYD DTC AI Analysis

Wiring harness damaged in front collision causing communication fault

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A BYD Qin Pro DM suffered collision damage to the front bumper and left fender. After body repairs, the vehicle set DTC B17A800 at startup. Inspection found the dash panel wiring harness (including the SRS-to-vehicle CAN adapter harness) compressed in the crash, damaging the CAN_H wire insulation and shorting it to ground. Resistance measured 0.5Ω between CAN_H and ground, infinity between CAN_L and ground. Repaired the damaged orange-black CAN_H wire with double-layer heat-shrink tubing and re-secured the harness clear of sharp metal edges. Checked the SRS ECU housing for deformation at the crash sensor mounting base; confirmed intact, then reinstalled the components and tested. Cleared the fault codes and read SRS live data, confirming normal crash sensor status and CAN communication.
BYD DTC AI Analysis

Faulty gateway module isolated SRS from vehicle network

✓
Multiple Qin PRO vehicles (2018-2019 MY) report DTC B17A800 with ABS, ESP, and VCU communication faults. The SRS module CAN lines measure normal individually, but the scan tool cannot access SRS data through the gateway. Inspect the gateway controller (behind the instrument panel; integrated in the BCM on some variants). An internal CAN distributor chip failure isolates the SRS network segment from the diagnostic CAN. Symptom: Direct connection to the SRS ECU works, but the OBD port cannot access it. Fix: Replace the gateway controller (or the complete BCM), perform network configuration programming (configure the communication matrix for all modules), and re-match the keys and immobiliser. This case shows the gateway's critical role in BYD vehicle communication.
Other Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
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.