AU
B132816

This DTC indicates the Battery Thermal Management Electric Water Pump supply voltage falls below the system normal operating threshold (typically below 9V or 10 — Seal U

Thermal Management System

This DTC indicates the Battery Thermal Management Electric Water Pump supply voltage falls below the system normal operating threshold (typically below 9V or 10.5V, depending on vehicle calibration).

In the BYD Qin EV thermal management system, this water pump circulates coolant between the battery pack and the heat exchanger to maintain cell temperature within the optimal 15–35°C operating range.

During an undervoltage fault, the pump may experience an abnormal speed drop, stop intermittently, or fail completely, reducing battery cooling and heating efficiency.

Prolonged operation with this fault can trigger the BMS power limit protection strategy (reduced-power driving) and, in extreme cases, pose a risk of battery thermal runaway.

The air conditioning controller (or thermal management controller) triggers this fault upon detecting an abnormal PWM feedback signal from the water pump or an abnormal power supply voltage.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Low-voltage battery (12V auxiliary battery) aging or low voltage: Voltage drops below 9V during vehicle startup, causing unstable power supply to the water pump.
  • 2Poor connection in the water pump power supply circuit or damaged wiring harness: high temperatures in the front compartment causing connector oxidation or backed-out pins, or body wiring harness wear increasing contact resistance and causing a voltage drop.
  • 3Water pump internal motor short circuit or seizure: Water pump bearing wear or a seized impeller abnormally increases operating current, pulling down the supply voltage.
  • 4Fuse or relay fault: Internally blown water pump power supply circuit fuse (typically 15A-20A), poor contact at the fuse base, or burnt relay contacts causing a voltage drop.
  • 5Thermal management controller output fault: The water pump PWM drive module or power output stage MOSFET is damaged and fails to provide stable voltage.
What To Do
  • 1
    Fault confirmation and Freeze Frame reading: Use the VDS2000/VDS6000 diagnostic tool to read the fault code, confirm if it is a current fault (Current), and record the ambient temperature, battery temperature, and water pump duty cycle data at the time of the fault.
  • 2
    Low-voltage battery check: Measure the 12V battery static voltage (≥12.4V) and startup voltage (≥9.6V). Check the battery state of health (SOH). Charge or replace the battery if necessary.
  • 3
    Power supply circuit measurement: Disconnect the negative terminal. Locate the battery thermal management water pump connector (usually on the right side of the front compartment or the front of the battery pack). Measure the voltage between connector Pin 1 (constant power) and Pin 2 (ground). With the ignition ON, the voltage must be ≥11.5V. If the voltage is below 10V, check fuse F1/16 or F2/13 (depending on vehicle configuration) and relay E13 in the front compartment fuse box.
  • 4
    Wiring harness continuity check: Measure the wiring harness resistance between the water pump connector and the thermal management controller (or air conditioning controller). Resistance must be <1Ω. Inspect the connector for backed-out pins, oxidation, or water corrosion. Focus on areas where the front compartment wiring harness rubs against the vehicle body.
  • 5
    Water pump load test: Use an oscilloscope to measure the voltage waveform during water pump operation. If the voltage drop exceeds 2V, directly connect an external 12V regulated power supply to test the water pump. If the water pump makes abnormal noise or the current is >8A (normal 2-4A), replace the water pump assembly.
  • 6
    Controller diagnosis: If the wiring and water pump are normal, check the thermal management controller software version. Upgrade to the latest version if necessary. Measure the voltage at the controller output terminal. If the output is abnormal, replace the controller.
  • 7
    Repair verification: Clear the fault code, start the air conditioning in cooling/heating mode, and verify the 'Battery Coolant Pump Speed' in the data stream reaches the target speed (usually 2000-4000 rpm). Perform a 30-minute road test to confirm the fault does not recur.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Oxidised water pump connector causing intermittent undervoltage on Qin EV

✓
The dashboard occasionally displayed 'Thermal Management System Fault'. DTC B132816 (current) retrieved. Inspection found the battery thermal management coolant pump on the right side of the front compartment, with a 3-pin waterproof connector. Disassembly revealed green corrosion inside the connector, and the Pin 1 (power) terminal had slightly backed out, causing increased contact resistance (measured 3.2 Ω). Fix: Cleaned the connector with WD-40 precision electrical contact cleaner, replaced the female terminal, applied conductive grease, and reconnected. Fault cleared.
BYD DTC AI AnalysisFrom Chinese market (translated)

Aging 12V battery caused cascading undervoltage failure in water pump

✓
The owner reported that after parking the vehicle overnight, the air conditioning failed to cool and a fault appeared on startup. Diagnosis found the 12V battery voltage was only 11.2V, dropping to 8.5V during startup. The thermal management controller triggered B132816 when its self-check detected the water pump voltage below threshold. After replacing the AGM 60Ah battery, startup voltage recovered to 10.2V and the fault code cleared automatically. This case suggests checking the low-voltage power supply system first.
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal short circuit in the water pump burned the fuse holder.

✓
Vehicle thermal management completely failed and battery temperature rose rapidly. Inspection found the water pump fuse (15A) in the front compartment fuse box had blown; it blew again immediately after replacement. Measured water pump resistance at only 0.8Ω (normal 3-5Ω). Disassembled the water pump and found a partial short circuit in the motor winding. Replaced the water pump assembly and repaired the burnt fuse holder (fitted a tin-plated copper sleeve to improve contact). Fault fully resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Wiring harness wear caused high-resistance connection and voltage drop

✓
Warning light illuminated when driving on rough roads. Inspection found the water pump power harness from the front compartment to the battery pack had lost its retaining clip at the firewall pass‑through, causing the harness to chafe against the metal body edge. This wore through the insulation and partially fractured the copper wires, creating an intermittent connection. Stationary voltage read 12V, but dropped below 8V over bumps. Repair: cut out the damaged section, spliced in 2.0 mm² high‑temperature silicone wire with soldered joints, and re‑secured the harness routing.
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]