AU
B2A0E12

This DTC indicates a short to battery in the signal circuit of the Battery Thermal Management System (BTMS) inlet coolant temperature sensor (typically located on the line before the battery cooling circuit enters the battery pack) — Atto 8

Thermal Management System

This DTC indicates a short to battery in the signal circuit of the Battery Thermal Management System (BTMS) inlet coolant temperature sensor (typically located on the line before the battery cooling circuit enters the battery pack).

The sensor utilizes an NTC (Negative Temperature Coefficient) thermistor and outputs a 0-5V analog voltage signal to the BMS or thermal management controller during normal operation.

During a short to battery (12V), the ECU detects a continuous signal voltage above the normal range (e.g., >4.8V or equal to battery voltage) and registers a short circuit fault.

This fault prevents the BMS from accurately reading the battery pack inlet coolant temperature, affecting the battery thermal management strategy and potentially triggering: 1) Disabled battery fast charging or limited discharge power; 2) False battery over-temperature protection triggers, forcing the battery cooling system (electric compressor, water pump) to operate; 3) Thermal runaway risk in extreme cases due to the inability to monitor actual battery temperature.

This is a severe DTC.

Inspect and repair immediately due to the high-voltage battery system thermal runaway risk.

The B2A0E12 fault code on the Atto 8 indicates a high-severity short to battery in the BTMS inlet coolant temperature sensor signal circuit. This can stop accurate battery coolant temperature readings and may limit charging or power. Common causes include a failed temperature sensor or damaged wiring shorting to a 12V supply. Visit an authorised dealer immediately for inspection and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Internal short circuit in the battery pack inlet coolant temperature sensor body (thermistor breakdown or internal package failure), shorting the signal terminal to the power supply terminal.
  • 2Worn or damaged sensor wiring harness insulation causes the signal wire to short to a vehicle 12V power wire (such as the reversing light power supply or a constant power circuit). This commonly results from chassis impacts or loose wiring harness retaining clips rubbing against sharp edges.
  • 3Water ingress or severe corrosion in the sensor connector (e.g., from wading or improper car washing) creates electrolytic conduction between the signal and power terminals inside the connector, causing a short circuit.
  • 4Internal sampling circuit fault in the thermal management controller (TMS) or battery management system (BMS), such as a burnt signal sampling resistor or scorched circuit board, causing a false external short circuit detection.
  • 5Improper repair procedures, such as a screw piercing the wiring harness during underbody guard installation, or incorrect harness wrapping during a previous repair compressing the harness against a power supply line and causing a short circuit.
What To Do
  • 1
    Safety Preparation: Wear insulated gloves, disconnect the high-voltage manual service disconnect (MSD), wait 5 minutes for the high-voltage system to discharge, and locate the battery pack inlet coolant temperature sensor (typically at the cooling pipe connection at the front of the battery pack).
  • 2
    Visual inspection: Check the sensor connector for looseness, backed-out pins, water ingress, or obvious burn marks. Check the wiring harness for damage at wear-prone areas such as the battery pack housing, crossmember, and underbody shield mounting points.
  • 3
    Disconnected sensor measurement: Unplug the sensor connector and measure the resistance across the two terminals of the sensor body. A normal NTC sensor measures 1-10kΩ at room temperature (varies with temperature). If the resistance is 0Ω or very low (<10Ω), the sensor has an internal short circuit. Replace the sensor.
  • 4
    Harness continuity test: Keep the sensor disconnected. Use a multimeter to measure the voltage from the harness connector signal wire (SIG) to body ground, and to the battery positive terminal. Normal voltage is 0V (or <0.1V). A 12V reading indicates a short to power. Inspect the harness routing to locate the damage.
  • 5
    Insulation test: Measure the insulation resistance between the signal wire and ground. The resistance must be >10MΩ. If the resistance is too low, repair or replace the wiring harness.
  • 6
    Component replacement verification: If the wiring harness is normal, replace the OEM imported coolant temperature sensor (verify the part number against the vehicle model year). Clear the fault code, power on, and verify the 'Battery Pack Inlet Temp' in the data stream displays correctly (matches actual temperature, no abnormal 12V value).
  • 7
    System function verification: Perform a battery cooling system function test. Verify the electric water pump and cooling fan operate normally with no other related fault codes present. Road test the vehicle to confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

2019 Qin EV sets DTC B2A0E12 and cannot fast charge after driving through water.

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After driving through flood water, the instrument cluster displayed "Check Powertrain" and fast charging failed. VDS retrieved DTC B2A0E12 (battery pack inlet water temperature sensor short circuit) along with multiple network faults. Inspection found water inside the battery pack front inlet water temperature sensor connector; severe green corrosion had shorted the signal terminal to the 12V reference supply. Repair: Cleaned the connector terminals with anhydrous alcohol, dried them, applied conductive paste, and repaired the sealing ring. The sensor internals were damaged, so the inlet water temperature sensor was replaced. After clearing the fault codes, the data stream showed inlet temperature back to normal at 28°C and fast charging restored.
BYD DTC AI Analysis

Wiring harness worn through and shorted after Qin EV underbody scrape

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The vehicle bottomed out while driving. No issues appeared initially, but DTC B2A0E12 triggered the following day accompanied by a "Battery temperature too high" warning. Raised on a lift, found the edge of an underbody shield mounting bracket had cut through the coolant temperature sensor wiring harness at the battery pack inlet. The signal wire (pink) contacted the reverse light power wire (red) at the damaged section, causing a short circuit. Stripped back the insulation, resoldered the signal wire, and applied double-layer heat shrink tubing. Rerouted the harness away from sharp edges and added corrugated tubing protection. Verified no short circuit remained, cleared the DTC, and road tested. Fault resolved.
BYD DTC AI Analysis

Internal short in Qin EV coolant temperature sensor causing false reading

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The vehicle suddenly set DTC B2A0E12 during normal operation, with the dashboard displaying a Thermal Management System Fault. Connected a scan tool and checked live data: Battery Pack Inlet Temp read -40°C or showed an abnormal 12V value (matching battery voltage). Disconnected the sensor connector and measured 0V on the harness side signal wire (normal), but 0.5Ω across the sensor terminals (near short). Diagnosed as internal thermistor breakdown. Replaced the battery pack inlet coolant temperature sensor (use OEM parts with matching resistance curves), refilled coolant and bled the system, cleared the fault codes. Live data then showed normal temperature readings varying with ambient temperature. Fault resolved.
BYD DTC AI Analysis

Qin EV aftermarket underbody shield crushed wiring harness, causing short circuit

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One week after the owner installed an aftermarket underbody guard, a B2A0E12 code appeared. Inspection found the mounting bolts were too long and pierced the protective sheath of the battery pack inlet coolant temperature sensor harness, shorting the signal wire to the bolt. The bolt connects to chassis ground, but at this location it was compressed against the reversing light power supply wiring. Fix: Removed the aftermarket guard. Repaired the harness by cutting out the damaged section and re-crimping the terminals. Replaced the bolts with OEM standard-length fasteners. Rerouted the harness to maintain at least 20 mm clearance from sharp metal edges and power cables. Replaced the damaged sensor. Fault resolved.
Other Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.