AU
B163B

This DTC indicates a Parking Assist System (PAS/PSD) fault — Seal U

Safety System

This DTC indicates a Parking Assist System (PAS/PSD) fault.

Specifically, the Left Rear Ultrasonic Sensor detects an abnormally low resistance signal (typically <0.8kΩ or a short to ground).

Normal ultrasonic sensor operating resistance ranges from 9-11kΩ.

The sensor transmits and receives 40kHz ultrasonic signals to detect the distance to rear obstacles.

The system sets this DTC when the sensor’s internal piezoelectric ceramic element shorts, wiring harness insulation chafes and grounds, connector water ingress shorts the signal wire to ground, or an incorrect sensor installation gap causes continuous false triggering.

This fault prevents obstacle detection in the vehicle’s left rear blind spot, causes missing or false reversing sensor warning tones, and severely compromises parking safety.

This DTC relates exclusively to the Parking Assist System, not the "front passenger side airbag" described in the original data.

Airbag resistance faults typically trigger other codes (such as the B163C series).

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left rear radar sensor damaged: Cracked or aged internal piezoelectric ceramic element, or seal failure, causes a short circuit and drops resistance to a very low level.
  • 2Wiring harness and connector fault: Crushed or chafed wiring harness inside the bumper causing a short to ground, or aged connector seals causing water ingress and pin oxidation, resulting in an abnormal signal.
  • 3Incorrect installation gap: Bumper modification, repair, or deformation causes the gap between the sensor and bumper surface to be too large (>2mm) or too small (<0.3mm), affecting ultrasonic transmission and triggering an impedance detection fault.
  • 4External contamination and physical damage: Thick mud, ice, or snow covers the sensor surface, or scraping cracks the housing, causing moisture ingress and an internal short circuit.
  • 5Parking Assist Controller (PAS ECU) fault: Damaged internal sampling circuit causes resistance detection deviation for the left rear radar channel (less common).
What To Do
  • 1
    Diagnostic tool check: Use VDS or Launch X-431 to read the fault code. Confirm whether B163B is Active or History. Check accompanying sub-codes (such as B163B-11 short to ground, B163B-13 open circuit) and record the freeze frame data.
  • 2
    Visual inspection: Check the left rear bumper radar sensor for cracks, dents, or contamination. Clean the sensor surface and verify the sensor is flush with the bumper surface (deviation <0.5mm).
  • 3
    Electrical measurement: Disconnect the sensor connector. Measure the supply voltage (should be >10 V, standard 12 V) and ground resistance (<1 Ω). Measure the signal wire to ground resistance (normally >10 MΩ, close to 0 Ω when faulty) and the sensor body resistance (normally 9–11 kΩ).
  • 4
    Signal waveform check: Use an oscilloscope to check the signal wire. A normal signal is a 40kHz pulsed square wave. If the display shows 0V or a continuous high level, confirm a wiring short circuit or damaged sensor.
  • 5
    Swap test: Swap the left rear and right rear radar sensors. If the fault code changes to B163C (right rear fault), the sensor is faulty. If the fault code remains B163B, check the wiring harness and ECU.
  • 6
    Wiring harness inspection: Inspect the wiring harness along its routing inside the bumper for damaged insulation or shorts to ground, focusing on bends and retaining clips. Repair the wiring harness if necessary and reinforce the waterproof insulation.
  • 7
    Replacement and calibration: After confirming the sensor fault, replace the left rear radar sensor (note the updated part number, e.g., with the -A suffix). Ensure the correct installation position, clear the fault code, and perform a system function test (verify using an obstacle at a distance of 20cm-150cm).
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song Pro left rear radar sensor unit damaged

✓
The owner reported the instrument cluster displayed 'Check parking assist system', with no warning sound from the left rear when reversing. Used VDS to retrieve DTC B163B (current code). Inspection revealed light scrapes on the left rear bumper and fine cracks on the sensor surface. Measured the sensor power supply as normal, but the signal line had no pulse output. Swapped the left rear and right rear sensors; the DTC moved to the right rear, confirming internal piezoelectric element failure in the sensor. Replaced the left rear radar sensor (part number: EA2E-2804411), cleared the DTC, and road tested. The parking function returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Pro DM: Intermittent radar fault (water ingress)

✓
The vehicle displayed an intermittent dashboard warning. The fault became more frequent after rain or washing. A diagnostic scan showed DTC B163B stored as a historical code, with subcode B163B-11 (short to ground). I found the left rear radar plug seal had deteriorated, with water inside and oxidised pins. The wiring harness showed normal continuity, but the signal occasionally dropped out. I replaced the radar plug (including the seal), cleaned the controller-side connector and applied conductive grease, then reinforced the harness seal with waterproof tape. After one week of follow-up, the fault did not recur.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Tang DM: Aftermarket bumper modification causes multiple radar faults

✓
After the owner fitted an aftermarket rear bumper, parking system faults developed and multiple DTCs logged, including B163B (left rear) and B163D (right rear). Inspection found the modified bumper's radar mounting holes misaligned; the left rear radar mounting gap measured 3 mm (standard 0.5–1.5 mm). The wiring harness was crushed and damaged, causing the signal wire to short to ground. Repaired the damaged harness and repositioned the sensor flush with the bumper outer surface. Cleared DTCs; B163B remained. Replaced the left rear radar sensor, permanently resolving the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song MAX radar sensor batch quality defect

✓
The dealership received multiple Song MAX vehicles built between March and May 2019. All reported left rear radar sensor failure with fault code B163B. Disassembling the faulty sensors revealed cold solder joints between the internal piezoelectric ceramic plates and circuit boards. The measured operating current was 0mA (normal: 15-25mA). The manufacturer issued Technical Service Bulletin TSB-2019-PAS-03, confirming a manufacturing defect in this sensor batch. Solution: direct replacement with the improved left rear radar sensor (new part number with suffix -A). The manufacturer covered the repair under warranty.
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. Sources: [1]