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B16C0

On BYD vehicles, DTC B16C0 indicates a front passenger Occupant Classification System (OCS) sensor fault, not an internal SRS ECU fault — Seal U

Safety System

On BYD vehicles, DTC B16C0 indicates a front passenger Occupant Classification System (OCS) sensor fault, not an internal SRS ECU fault.

The system detects seat load status using a capacitive or piezoresistive pressure-sensing membrane inside the front passenger seat cushion.

It distinguishes between an adult, a child, or an unoccupied seat to control the front passenger airbag deployment strategy (deployment decision, timing, and force).

When the SRS ECU detects an OCS sensor signal open circuit, short circuit, out-of-range value, or incomplete calibration, it sets this DTC and illuminates the airbag warning lamp.

This fault creates an extreme safety risk: the system may incorrectly identify the seat as unoccupied and disable airbag deployment, or erroneously deploy the airbag when a child seat is installed.

This safety hazard requires immediate repair.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Oxidation, loose connection, or poor contact at the yellow 2-pin harness connector under the seat, causing signal interruption or abnormal resistance.
  • 2Prolonged chafing between the wiring harness and the metal seat frame damages the insulation, causing a short to ground or a short to power.
  • 3OCS sensor mat cut, folded, or physically damaged during front passenger seat modification (leather retrimming, foam replacement).
  • 4Failure to perform the OCS (Occupant Classification Calibration) procedure after replacing the seat assembly or airbag ECU, resulting in an unwritten sensor ID or uncalibrated weight threshold.
  • 5Sensor body internal circuit aging, corrosion from water ingress, or capacitor/resistor value drift causes the output signal to exceed the ECU-recognized threshold range (2.5kΩ-3.0kΩ is the normal no-load value).
What To Do
  • 1
    Connect the VDS2000 or X431 diagnostic tool and access the SRS system to read the fault code and freeze frame data. Check the 'Passenger Seat Status' and 'OCS Sensor Resistance' values in the data stream to confirm whether the fault is permanent or intermittent.
  • 2
    Disconnect the yellow connector under the front passenger seat (usually located ahead of the seat slide rail). Inspect the pins for oxidation or backing out. Clean the pins with electrical contact cleaner and apply conductive grease. Measure the resistance between the connector terminals (normal no-load resistance is 2.5 kΩ–3.0 kΩ; resistance changes when occupied).
  • 3
    Inspect along the seat wiring harness routing to the floor harness connection point. Pay special attention to the contact areas between the harness, seat frame, and slide rails. If the harness shows wear or damaged insulation, cut out the damaged section and solder an extension wire. Apply heat-shrink tubing and waterproof tape for double-layer insulation. Re-secure the harness with cable ties, maintaining a clearance of at least 20mm.
  • 4
    If wiring harness continuity is normal but sensor resistance is abnormal (infinite, shorted, or a fixed value that does not change with pressure), replace the front passenger seat cushion assembly (including the integrated OCS sensor mat). Do not disassemble the sensor mat separately for repair.
  • 5
    After replacing the component or repairing the wiring harness, enter the diagnostic tool 'Special Functions' → 'Passenger Classification System Calibration'. Follow the prompts to place standard weights of 5kg (simulating a child seat) and 75kg (simulating an adult) in sequence to complete the sensor zero-point and full-scale calibration.
  • 6
    Clear the fault code and perform a 20-minute dynamic road test (including bumpy roads). Confirm the instrument cluster airbag warning light turns off, the data stream seat status correctly switches between 'Empty' and 'Occupied' based on occupancy, and the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

Oxidised wiring harness connector on Tang DM caused intermittent fault

✓
2019 BYD Tang DM, 32,000 km. The airbag warning light on the dash would illuminate intermittently with no set pattern, easily triggered after driving over speed bumps. VDS pulled fault code B16C0 (passenger seat occupancy sensor signal abnormal/open circuit), alternating between current and history. Under-seat inspection found green oxide inside the yellow connector. Resistance measurement showed the sensor open circuit (infinite resistance) when shaken. Cleaned the connector pins, applied conductive grease, and replaced the wiring harness connector (part no. BYD-282104-XXXX). Cleared the fault codes and road tested—issue resolved.
Original source ↗
BYD DTC AI Analysis

Han EV OCS uncalibrated after accident repair

✓
2021 BYD Han EV. After repairs following a right-front side collision, the airbag warning light stayed on constantly. VDS read code B16C0 (front passenger OCS sensor not calibrated); live data showed seat status always 'Empty'. Diagnosis found the accident repair had used a lower-spec salvaged seat, the sensor ID didn't match the vehicle, and the calibration option in VDS was greyed out. Replaced the front passenger seat cushion assembly with a new genuine unit (Part No.: SCEA-XXXXXXXX). Performed passenger classification system calibration using 5kg and 75kg standard weights. Fault cleared after successful calibration.
Original source ↗
BYD DTC AI Analysis

Aftermarket seat modification on Qin Pro caused sensor damage

✓
2020 BYD Qin Pro. Airbag warning light stayed on after leather seat modification, with DTCs B16C0 (Sensor Performance Range) and B16C1 (Hardware Failure). Disassembly revealed the modification blade had sliced through the OCS sensor mat inside the seat cushion. Resistance measured only 120 Ω (near short circuit). Replaced the genuine front passenger seat occupancy sensor together with the cushion foam (part number: F3-XXXXXXXX). Advised the owner to always transplant the original sensor mat intact during future seat modifications, and then perform the calibration procedure.
Original source ↗
BYD DTC AI Analysis

Song Plus DM-i wiring harness chafing against frame

✓
2022 BYD Song Plus DM-i, 18,000 km. After starting, the airbag warning light flashes for 6 seconds then stays on continuously, displaying 'Please check airbag system'. DTC B16C0 (passenger seat occupancy sensor circuit short to ground). Inspection found an unsecured wiring harness under the seat, rubbing against the metal frame and causing the 5V supply wire to wear through and short to ground, putting the ECU into protection mode. Repaired the damaged harness by soldering and insulating with heat-shrink tubing, re-secured the harness routing with clearance from the frame, cleared the fault codes, and the data stream returned to normal.
Original source ↗
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.