AU
B168D00

DTC B168D00 indicates the Airbag Control Unit (ACU) detects invalid configuration data for Ignition Loop 9 — Atto 8

Safety System

DTC B168D00 indicates the Airbag Control Unit (ACU) detects invalid configuration data for Ignition Loop 9.

In the BYD Qin PRO SRS system, Loop 9 typically corresponds to the front passenger knee airbag or rear seat side airbag circuit, depending on the vehicle configuration level. "Invalid configuration" means the "configuration present flag", "rated resistance parameter", or "capacity type" in the ACU EEPROM data does not match the installed hardware.

This condition also occurs if the ACU detects a load on a circuit marked "not installed", or detects an open circuit on a loop marked "installed".

This fault causes the ACU to enter degraded mode.

During a collision, the ACU may fail to deploy the airbag on this circuit, or it may trigger a fail-safe strategy that restricts overall SRS functionality.

3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Failure to write configuration data, or writing incorrect data, after replacing the Airbag Control Unit (ACU) (e.g., installing a used ACU with a stored configuration that does not match the original vehicle configuration).
  • 2ACU internal data corrupted after a vehicle collision, or failure to update configuration parameters after replacing the airbag assembly (e.g., installing a high-spec airbag in a low-spec vehicle without reconfiguring).
  • 3Poor contact, short circuit, or abnormal resistance in the Circuit 9 wiring harness connector causes the ACU to incorrectly detect a configuration error (actual hardware does not match the configuration).
  • 4ACU software version defect or programming error causing configuration data verification failure.
  • 5Battery depletion or incorrect procedures during power disconnection maintenance caused the loss or corruption of configuration data in the ACU non-volatile memory.
What To Do
  • 1
    Connect the VDS2000 or the BYD dedicated diagnostic tool to the vehicle. Read the complete fault codes, confirm B168D00 is a current fault (Active), and record the freeze frame data.
  • 2
    Confirm the specific vehicle configuration: Check the vehicle VIN and configuration sheet to verify the vehicle actually has the specific component corresponding to Circuit 9 (knee airbag/rear side airbag) installed.
  • 3
    Check the ACU software version. If a newer version is available, update the software to rule out false alarms caused by software defects.
  • 4
    Access the SRS system 'Special Functions' menu and execute the 'ECU Configuration' or 'Write Configuration Data' function. Reconfigure the circuit 9 status (enable/disable) and parameters based on actual vehicle equipment.
  • 5
    If configuration fails or the fault persists after configuration, disconnect the battery negative terminal. Check the circuit 9 wiring harness connector (usually located under the passenger dashboard or seat). Measure the circuit resistance (standard value is usually 1.8-2.5Ω) to rule out a short or open circuit in the wiring.
  • 6
    If the wiring harness is normal but configuration still fails, replace the ACU with a new unit (ensure the part number matches the vehicle configuration). Perform online configuration, coding, and security verification code (PIN) entry.
  • 7
    Reconnect the battery, clear the fault code, and perform the SRS system self-check (turn the ignition switch to the ON position and wait approximately 10 seconds for the system self-check to complete).
  • 8
    Use the diagnostic tool to perform the 'Collision Output Test' (Simulation Test) to verify circuit 9 status. After confirming no fault codes are present, perform a road test on a bumpy surface to confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM ACU not reconfigured after accident repair

✓
A 2019 BYD Qin PRO DM had its airbag control unit replaced with a used unit from the same model at a non-authorised workshop after a front-end collision. The airbag warning light came on, and a scan revealed DTC B168D00. The used ACU came from a base-model car without a passenger knee airbag, while this vehicle is a high-spec variant with one. We ordered a new ACU with the correct high-spec part number. After fitting it, we ran the ‘ACU Replacement’ procedure on the diagnostic tool and programmed the configuration to enable circuit 9. The fault cleared.
BYD DTC AI Analysis

Configuration data lost after software upgrade

✓
A 2018 Qin PRO petrol variant developed an airbag warning light on the instrument cluster after an SRS system software upgrade at the dealership. The diagnostic tool retrieved DTC B168D00. Investigation revealed unstable battery voltage during the upgrade caused the configuration data write to fail. Repair: Checked circuit 9 harness and airbag connector – both normal. Used the diagnostic tool to enter 'System Configuration' and manually changed circuit 9 status from 'Disabled' to 'Enabled' (as the vehicle is actually fitted with a knee airbag). Wrote the configuration, cleared the DTC, and the system returned to normal.
BYD DTC AI Analysis

Loose wiring connection caused misdiagnosis as configuration error.

✓
A 2019 Qin Pro DM had an intermittent airbag warning light while driving. Retrieved DTC B168D00 (intermittent). Inspection found the passenger knee airbag connector (behind the glovebox) had a loose connection due to an assembly fault, causing the ACU to detect intermittent circuit resistance (open circuit state), conflicting with the stored 'installed' configuration. Repair: re-secured the wiring harness, cleaned and tightened the connector terminals. Measured circuit resistance stable at 2.1Ω. Cleared the fault code and monitored for one week with no recurrence.
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.