AU
B16AC

For BYD new energy models (Qin, Tang, Song, Yuan, and Han series), DTC B16AC indicates an air conditioning evaporator temperature sensor circuit fault (Evaporator Temperature Sensor Circuit Range/Performance), not the SRS_ECU fault stated in the original information — Seal 6 EV

Safety System

For BYD new energy models (Qin, Tang, Song, Yuan, and Han series), DTC B16AC indicates an air conditioning evaporator temperature sensor circuit fault (Evaporator Temperature Sensor Circuit Range/Performance), not the SRS_ECU fault stated in the original information.

This NTC thermistor mounts on the air conditioning evaporator surface.

It monitors the evaporator temperature in real time to prevent surface icing from blocking the air ducts.

The controller sets this DTC and triggers the air conditioning system protection strategy (compressor shutdown or restricted cooling) upon detecting an out-of-range sensor signal voltage (close to 5V during an open circuit, close to 0V during a short circuit, or unresponsive to temperature changes), abnormal resistance, or an abnormal sampling frequency.

This fault results in a lack of cooling, intermittent A/C operation, or evaporator icing.

The B16AC fault code on the Seal 6 EV indicates an air conditioning evaporator temperature sensor circuit malfunction, causing poor cooling or intermittent A/C operation. The system protects itself by shutting down the compressor when the sensor reports out-of-range values due to wiring damage or sensor failure. Severity is medium. Fix requires visiting an authorised dealer. Typical repair cost data is available based on 5 recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Faulty evaporator temperature sensor: Internal thermistor open circuit, short circuit, or resistance drift fixes the signal voltage at a specific value (such as 4.9V or 0.1V) regardless of temperature.
  • 2Wiring harness open circuit or poor contact: Repeated bending or interference at the glovebox hinge or firewall pass-through breaks the signal wire, 5V reference voltage wire, or ground wire from the sensor to the air conditioning controller.
  • 3Connector oxidation or looseness: High humidity near the passenger-side evaporator housing forms copper corrosion or an oxide layer on the sensor connector terminals, resulting in contact resistance fluctuations (0.5Ω-50Ω variation).
  • 4Wiring harness chafing and short circuit: Incorrect routing causes the wiring harness to interfere with the body sheet metal. Worn insulation shorts the signal wire to ground, causing the controller to detect an abnormally low voltage.
  • 5Control module software fault: Air conditioning controller software in certain batches is sensitive to temperature signal spikes or contains sampling algorithm defects, causing false sensor circuit fault reports during sun exposure or high-load operating conditions.
What To Do
  • 1
    Connect the VDS or X431 diagnostic tool, access the air conditioning system, and read the fault codes. Confirm whether B16AC is a current fault (Active) or a history fault (History). Record the ambient temperature and evaporator temperature values from the freeze frame data.
  • 2
    Read the data stream and observe the 'evaporator temperature sensor' value. During cooling, the value should gradually drop from ambient temperature (25-30°C) to 2-5°C. A reading of -40°C, -25°C, 85°C, or a fixed unchanging value indicates an abnormal signal.
  • 3
    Remove the front passenger glovebox (usually requires removing the damper and retaining screws) to expose the evaporator housing. Locate the evaporator temperature sensor (two-wire or three-wire connector, pink/yellow signal wire).
  • 4
    Measure the sensor resistance: the standard value at 25°C is approximately 1.5-2.5kΩ. Grasp the sensor head; the resistance must decrease as the temperature rises (NTC negative temperature coefficient characteristic). Replace the sensor if the resistance is infinite (open circuit) or close to 0Ω (short circuit).
  • 5
    Measure circuit continuity: Disconnect the battery negative terminal and the air conditioning controller connector. Measure the continuity of the signal wire, power wire, and ground wire between the sensor connector and the controller. Inspect the wiring harness for breaks or chafing, focusing on the glove box hinge and the firewall pass-through.
  • 6
    Check the connector condition: Inspect male and female terminals for green corrosion (oxidation) or looseness, clean with electronic contact cleaner, apply conductive grease to improve contact, and adjust terminal tension if necessary.
  • 7
    If the wiring and sensor are normal, check the air conditioning controller software version against the BYD Technical Service Bulletin (TSB). If a relevant software update is available (such as V2.3 for the Han EV), flash the controller software.
  • 8
    After repair or replacement, restore all connections and clear the fault codes. Start the vehicle and set the air conditioning to maximum cooling mode. Observe the data stream to verify the evaporator temperature drops normally and confirm the compressor no longer stops abnormally.
Real-World Cases
BYD DTC AI Analysis

BYD Song Pro DM evaporator sensor circuit open

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Symptoms: With A/C on, the system blows ambient air only. Compressor does not engage – no cooling. Intermittent fault. Diagnosis: Connected a Launch X431 and read the A/C system. Retrieved DTC B16AC: Evaporator Temperature Sensor Circuit Open. Removed the glovebox and measured infinite resistance at the sensor connector (spec: 1.5–2.5 kΩ). Traced the pink signal wire between the sensor and controller; found it broken at the glovebox hinge from repeated bending. Repair: Soldered the broken harness wires and sealed with heat-shrink tubing. Rerouted and secured the wiring harness to prevent chafing. Cleared the DTCs – A/C returned to normal operation. Sensor not replaced.
Original source ↗
BYD DTC AI Analysis

BYD Qin Plus EV sensor connector oxidised, poor contact

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Symptoms: Air conditioning cooling intermittent, evaporator surface frequently icing up, airflow gradually decreasing. Stored DTC B16AC. Diagnosis: Data stream showed evaporator temperature -25°C (actual ambient 30°C) — signal abnormal. Inspected connector, found obvious green corrosion and oxidation on male/female terminals. Sensor body resistance measured normal, but contact resistance fluctuated between 0.5Ω and 50Ω when connected. Resolution: Cleaned connector terminals with electronic contact cleaner, applied conductive grease to improve contact, reconnected and wrapped with waterproof tape. Fault resolved, no parts replaced.
Original source ↗
BYD DTC AI Analysis

Damaged thermistor in BYD Tang DM sensor body

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Symptoms: The A/C stopped working after 5–10 minutes of operation. It recovered after restarting but shut down again shortly after. The temperature display on the A/C panel showed '--' or a fixed 85°C. Diagnosis: Scan tool retrieved active fault B16AC and communication loss code U0164. Sensor supply voltage measured 5V and ground was normal, but signal wire voltage stuck at 4.9V and did not vary with temperature. Fitted a new sensor for comparison – signal voltage returned to normal, varying from 1.2V to 3.8V with temperature changes. Repair: Replaced the A/C evaporator temperature sensor (part no. EG-8103010). Removed the passenger-side dashboard and evaporator housing to access it. Recharged refrigerant and test drove – fault did not return.
Original source ↗
BYD DTC AI Analysis

BYD e5 taxi wiring harness chafed causing short to ground

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Symptom: Air conditioning suddenly cuts out when driving on rough roads but works normally on smooth surfaces. B16AC is an intermittent fault code; freeze frame data shows the vehicle was on uneven terrain when the fault occurred. Diagnosis: Inspected the wiring harness routing and found it chafing against the body sheet metal where it passes through the firewall. Stripped back the corrugated conduit to reveal the signal wire insulation worn through, exposing the copper strands. The wire intermittently shorts to ground when the vehicle bounces. The sensor itself tested normal; the controller logged B16AC (signal voltage below threshold) when the short occurred. Repair: Repaired the wiring harness with electrical tape and heat-shrink tubing. Re-routed the harness and fitted a rubber grommet at the firewall opening. Installed a foam sleeve at the rubbing point to prevent further chafing.
Original source ↗
BYD DTC AI Analysis

BYD Han EV control module software false-positive fault detection

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Symptoms: Air conditioning stopped cooling at 5,000 km on a new vehicle. Scanned DTC B16AC. Measured the sensor and wiring circuits—both completely normal. The fault occurred more frequently after the vehicle had been parked in the sun. Diagnosis: Measured sensor resistance and voltage—both within specification (approximately 1.8 kΩ at 25°C, signal voltage 2.3 V). Compared the data stream against a known-good identical vehicle; identified abnormal sensor sampling frequency on the faulty vehicle. Consulted the BYD technical service bulletin; confirmed certain batches of AC controller software are sensitive to temperature fluctuations, causing false B16AC codes. Solution: Updated the AC controller software to the latest version (V2.3 or higher). After flashing, monitored the data stream—temperature sampling smoothness improved. The DTC has not returned. Did not replace any hardware.
Original source ↗
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.