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B172211

DTC B172211 indicates the Supplemental Restraint System (SRS) detects an abnormally low-resistance path (short circuit) to body ground in the right knee airbag (passenger-side knee airbag) ignition circuit — Atto 3

Safety System

DTC B172211 indicates the Supplemental Restraint System (SRS) detects an abnormally low-resistance path (short circuit) to body ground in the right knee airbag (passenger-side knee airbag) ignition circuit.

Under normal conditions, the airbag igniter circuit resistance should be between 2.0 and 3.0 Ω.

The ECU determines a short to ground when it detects circuit resistance below 1.0 Ω or voltage to ground near 0 V.

This fault prevents proper airbag deployment during a collision (as the ECU disables the circuit to protect the power supply) or, in extreme cases, causes unintended deployment.

Simultaneously, the SRS enters fail-safe mode, illuminates the airbag warning light, and may lock the entire airbag system, severely compromising passive safety performance.

4
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Knee airbag connector oxidised and shorted on water-wading vehicle

✓
A 2019 Qin PRO DM developed an airbag warning light that stayed on after wading through water during heavy rain. DTC B172211 was stored. Inspection found obvious water residue inside the right knee airbag connector (located behind the glovebox), with the copper pins oxidized and blackened. The air conditioning drain hose had detached, allowing condensation to accumulate over time. Cleaned the connector pins, dried the wiring harness with compressed air, replaced the AC drain hose, applied conductive grease and reset the system. Fault resolved.
BYD DTC AI Analysis

After accident repairs, the dashboard frame pinched the wiring harness.

✓
A 2018 Qin Pro petrol model developed DTC B172211 one month after front-end collision repairs. Inspection found the right knee airbag harness pinched where it passes through the instrument panel crossbeam mounting bracket. The insulation had chafed through, exposing copper wire, which made direct contact with the vehicle body and created a short to ground. The cause was improper assembly during the accident repair – the harness was not routed to specification. Repaired the wiring by cutting out the damaged section, soldering the joint and sealing with heat-shrink tubing. Rerouted the harness correctly and fitted protective corrugated tubing. Fault cleared.
BYD DTC AI Analysis

Internal short circuit in knee airbag module igniter

✓
A 2020 E3 airbag warning light suddenly illuminated during normal use, logging DTC B172211. Disconnected the airbag connector—harness-side resistance to ground measured normal (infinite). Measured 0.3Ω between pins of the airbag module (lower right of dashboard), indicating an internal short. Replaced the right knee airbag module and used a scan tool to perform coding and configuration (some models require a new airbag ID). Fault resolved. The old module was returned to the manufacturer for analysis, who confirmed an insulation defect in the internal bridge wire.
BYD DTC AI Analysis

Intermittent fault caused by SRS ECU misjudgement

✓
A 2019 E2 intermittently logged DTC B172211, appearing when cold and disappearing when warm. We measured the wiring harness and airbag resistance; both were within normal range. We suspected a fault in the ECU's internal sampling circuit. After replacing the SRS ECU with an identical unit (which required immobiliser and VIN recoding), the fault vanished. Analysis pointed to a drift in the ground-sampling resistor of the ECU's monitoring chip, causing a false short-circuit alert. In similar cases, distinguish between actual wiring shorts and ECU hardware faults.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.