AU
B132971

This DTC indicates the electric water pump in the battery thermal management circuit (typically located in the battery pack liquid-cooling circuit or battery heat pipe circulation branch) detects a locked rotor condition — Seal U

Thermal Management System

This DTC indicates the electric water pump in the battery thermal management circuit (typically located in the battery pack liquid-cooling circuit or battery heat pipe circulation branch) detects a locked rotor condition.

Specifically, the pump control module detects the drive current continuously exceeding the threshold (typically 3-5 times the rated current) while the speed feedback signal remains at zero or extremely low, determining a mechanical rotor seizure.

This is a hard fault.

Upon triggering, the thermal management controller immediately cuts pump power to protect the drive circuit.

Consequences include interrupted battery pack coolant circulation, causing loss of battery temperature control during fast charging and reduced heat pump air conditioning heating efficiency (if equipped with a water-source heat pump system).

Continued operation may trigger BMS power derating protection or high-voltage system shutdown.

The DTC suffix '71' typically serves as a subtype identifier indicating a persistent locked rotor condition rather than a momentary overload.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Water pump impeller mechanically jammed: After long-term use, limescale, coolant corrosion products, or external contaminants enter the pump chamber and seize the impeller against the pump housing; or in low temperatures (below -20°C), localized coolant freezing and expansion jam the impeller.
  • 2Motor drive circuit fault: A damaged MOSFET half-bridge driver chip inside the water pump controller causes abnormal three-phase drive waveforms. The motor fails to generate an effective rotating magnetic field and enters a DC braking state (exhibiting stall current characteristics).
  • 3Electrical connection fault: A loose water pump wiring harness connector, backed-out terminals, or water ingress causing oxidation leads to phase loss in the three-phase power supply. Insufficient torque prevents the motor from starting, resulting in a stall.
  • 4Water pump bearing seizure: Prolonged dry running (caused by coolant leakage) or bearing defects cause rotor-to-stator rubbing (mechanical friction) and rotor lock-up.
  • 5Control logic fault: The thermal management controller outputs an abnormal PWM control signal duty cycle (e.g., always 100% or incorrect frequency), causing the motor drive module to enter protective lockout.
What To Do
  • 1
    Initial diagnosis: Read all DTCs using the VDS2000/3000 diagnostic tool. Check for related fault codes (such as B132A00 idling fault and U0121 communication fault). Record the battery temperature, ambient temperature, water pump duty cycle, and current values from the freeze frame data.
  • 2
    Safety preparation: Disconnect the low-voltage battery negative terminal, wait 5 minutes to discharge the high voltage, confirm the cooling system has no pressure (slowly open the expansion tank cap), and wear insulated gloves during operation.
  • 3
    Visual and mechanical inspection: Inspect the water pump mounting bracket for breaks causing axial load. Remove the motor end cover and manually rotate the water pump impeller to check for seizing. Check the coolant for cloudiness or metal debris.
  • 4
    Electrical measurement: Disconnect the wiring harness connector. Measure the water pump three-phase winding resistance (normal value 2-5 Ω, three-phase balance <5%). Measure the connector insulation resistance to ground (must be >20 MΩ). Check the 12 V power supply and PWM signal wire (normal PWM frequency 100-500 Hz, duty cycle adjustable 0-100%).
  • 5
    Load test: Drive the water pump directly using an external adjustable power supply (first test rotation at 2V, then increase to 12V). Observe the no-load current (normal: 0.5-1.5A). If the current is >5A and the speed is low, it indicates internal mechanical binding.
  • 6
    Replacement verification: Replace the water pump assembly (verify the model matches; distinguish between the integrated and standalone electronic three-way valve types). Perform the 'Thermal Management Water Pump Bleeding' special function and complete adaptive learning.
  • 7
    System verification: Start the vehicle, activate the air conditioning heating mode, and read the data stream to confirm the coolant pump target speed matches the actual speed (typically 1000-6000 rpm). Observe for 10 minutes to verify the fault code does not recur. Check the expansion tank coolant level and top up.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV coolant crystallisation causing periodic water pump seizure

✓
2019 BYD Qin EV, 62,000 km. Dash displayed "Thermal Management Fault" during fast charging. Scan tool retrieved DTC B132971. Freeze frame data indicated battery temperature at 42°C when the fault occurred, coolant pump duty cycle at 100%, and drive current at 8.5 A (normal 3 A). Disassembled the pump and found heavy white ethylene glycol crystal deposits between the impeller and housing, caused by prolonged failure to replace the coolant. Replaced the pump, flushed the cooling circuit thoroughly, and refilled with low-conductivity coolant (BYD specification LG-2). Fault resolved. Recommend replacing coolant every 40,000 km.
BYD DTC AI AnalysisFrom Chinese market (translated)

Loose wiring harness connection caused water pump phase loss and locked rotor

✓
2019 Qin EV. Intermittent fault reported on rough roads. Water pump tested normal statically; wiggling the harness reproduced the fault. Inspection found a backed-out terminal pin in the GJB02 connector (water pump power plug) inside the left front wheel arch liner, causing poor contact on one phase. With phase loss, the water pump produced insufficient starting torque. The controller detected overcurrent but no speed feedback and judged the motor as stalled. Repaired the harness terminal, applied conductive paste, and wrapped with waterproof tape. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Water pump bearing seized, causing rotor-to-housing contact

✓
One month after wading through water, the fault appeared. Disassembly revealed the rotor bearing seized due to corrosion, causing the rotor to contact the stator (scuffing) with visible scoring on the rotor surface. Water entered through the pump breather during wading. Although the pump is rated IP67, the seal had deteriorated. Replaced the water pump assembly. Also checked insulation on other pumps in the same circuit (e.g., motor coolant pump) to prevent consequential damage. After wading, inspect thermal management system seals promptly.
BYD DTC AI AnalysisFrom Chinese market (translated)

Controller MOSFET breakdown causing drive malfunction

✓
This DTC appeared alongside 'Battery heat pipe electric water pump overvoltage fault B132817'. Measured the pump body resistance as normal and the impeller turned freely by hand. Inspected the water pump controller (separate from the HVAC controller on some models) and found one MOSFET (model IRFB3607) on the drive board with a drain-source breakdown short circuit. This caused two motor phases to short-circuit, producing a DC braking effect. Replaced the water pump controller (or the pump assembly with integrated controller) and the fault was resolved. Replacing the controller alone requires reflashing the parameter configuration.
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]