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 — Atto 3

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.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Evaporator temperature sensor failure: Internal thermistor open circuit, short circuit, or resistance drift causes the signal voltage to remain fixed at a specific value (such as 4.9V or 0.1V) regardless of temperature.
  • 2Wiring harness open circuit or poor contact: The signal wire, 5V reference voltage wire, or ground wire from the sensor to the air conditioning controller breaks at the glovebox hinge or firewall grommet due to repeated bending or interference.
  • 3Connector oxidation or looseness: High humidity near the front passenger evaporator housing causes copper corrosion or an oxide layer to form on the sensor connector terminals, resulting in contact resistance fluctuations (0.5Ω-50Ω).
  • 4Wiring harness abrasion short circuit: Improper harness routing causes interference with body sheet metal. Worn insulation shorts the signal wire to ground, causing the controller to detect abnormally low voltage.
  • 5Control module software fault: A/C controller software in certain batches is sensitive to temperature signal spikes or has sampling algorithm defects, triggering false sensor circuit faults during sun exposure or high-load operation.
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 the cooling process, it 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 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 body resistance: the standard value at 25°C ambient temperature is approximately 1.5–2.5 kΩ. Hold the sensor head; resistance should decrease as temperature rises (NTC negative temperature coefficient characteristic). Replace the sensor if resistance is infinite (open circuit) or close to 0 Ω (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 wear, especially at the glovebox hinge and firewall pass-through.
  • 6
    Check plug connection condition: Inspect male and female terminals for green corrosion (oxidation) or looseness. Clean with electrical contact cleaner, apply conductive grease to improve contact, and adjust terminal tension if necessary.
  • 7
    If the wiring and sensor are normal, check the A/C controller software version against the BYD Technical Service Bulletin (TSB). If a relevant software upgrade program 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. Check 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

✓
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

✓
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

✓
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

✓
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

✓
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 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: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.