AU
U014987

DTC U014987 indicates a communication link interruption between the battery thermal management controller (usually integrated into the Battery Management System (BMS) or a separate thermal management control unit) and the battery thermal circuit electric coolant pump — Seal U

Thermal Management System

DTC U014987 indicates a communication link interruption between the battery thermal management controller (usually integrated into the Battery Management System (BMS) or a separate thermal management control unit) and the battery thermal circuit electric coolant pump.

This pump drives battery coolant circulation and typically uses LIN bus (CAN bus on some models) for digital communication.

The controller triggers this fault when it fails to receive pump status feedback signals (such as speed, temperature, or fault status) within a specified period (generally 100-200ms), or when it cannot send control commands (such as target speed requests).

This fault forces the battery thermal management system into open-loop control or degraded mode, limiting fast-charging power and power output.

Extreme cases may trigger battery high-temperature protection.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Electric water pump power supply circuit fault: Includes a blown 15A/20A fuse, an open circuit, or a poor connection in the power supply line, preventing the water pump control module from operating normally.
  • 2LIN/CAN communication circuit fault: short to ground, short to power, open circuit, or excessive contact resistance (>5Ω). This fault typically occurs at harness bends near the battery pack or the firewall wiring grommet.
  • 3Electronic water pump assembly fault: damaged internal brushless motor drive circuit, seized motor rotor, damaged LIN transceiver chip, or triggered internal overheat protection.
  • 4Connector issue: Water ingress, oxidation, terminal back-out, or locking mechanism failure at the battery pack low-voltage connector (usually located at the front of the battery pack near the BJB or service disconnect switch)
  • 5Thermal management controller or gateway fault: damaged controller internal communication chip, software version defect, incorrect gateway routing table configuration, or abnormal terminating resistor.
What To Do
  • 1
    Use the VDS diagnostic tool to read all fault codes, confirm if U014987 is a current fault, check for accompanying communication fault codes, and view the freeze frame data (record parameters such as battery temperature and requested water pump speed when the fault occurred).
  • 2
    Visually inspect the electric water pump appearance and installation. Confirm no coolant leakage, abnormal noise, or mechanical damage to the wiring harness. Specifically check that the low-voltage connector at the front of the battery pack is fully locked and shows no signs of water ingress.
  • 3
    Disconnect the electric water pump connector. Measure the voltage between the constant power pin (usually B+) and body ground; it should be 12V±0.5V. Measure the resistance between the ground wire pin and body ground; it should be <1Ω. Check if the fuse is blown.
  • 4
    Measure communication line voltages and waveforms (LIN line normally approx. 9-11 V, CAN-H approx. 2.6-2.8 V, CAN-L approx. 2.2-2.4 V). Use an oscilloscope to check for signal distortion. Measure circuit resistance to confirm no open or short circuits.
  • 5
    Check the connector pins for green copper corrosion, pin back-out, or enlarged pin holes. Repair the pins using the special tool. Clean the pins, apply electrical contact protectant, and verify the connector waterproof seal is intact.
  • 6
    Perform an active test: Use the diagnostic tool to command the water pump to run and listen for pump operation. If the pump fails to actuate, swap in a known-good electric water pump to verify whether the fault follows the component.
  • 7
    Check the thermal management controller: Measure wiring harness continuity from the controller to the water pump (resistance <1Ω). Check the controller software version and update to the latest version. Replace the thermal management controller or gateway module if necessary.
Real-World Cases
BYD DTC AI Analysis

Poor contact in the front-end wiring harness of the Qin EV battery pack caused an intermittent communication fault.

✓
A 2019 Qin EV intermittently displayed "Check Power System" on the instrument cluster while driving, accompanied by DTC U014987. Technicians connected a VDS scan tool and reviewed live data; the battery thermal management pump status showed "communication timeout" when the fault occurred. They inspected the low-voltage harness connector at the front of the battery pack where it mates to the body harness and found an intermittent loose connection at the LIN bus terminal, with resistance fluctuating between 0.5 and 50 Ω. Disassembling the connector revealed a fractured internal locking clip that caused the terminal to back out. Solution: Replaced the battery pack low-voltage harness assembly, re-crimped the terminals and applied conductive paste. Technicians ran the thermal management system self-test with VDS and confirmed the fault cleared.
Original source ↗
BYD DTC AI Analysis

Loose ground point on Qin EV thermal management water pump caused communication loss

✓
A Qin EV lit the powertrain warning light while driving on rough roads. Scanning showed DTC U014987 (Lost communication with battery thermal management electric water pump). The fault returned when the vehicle bounced. Diagnosis found a loose bolt at ground point G107 (on the left front frame rail), causing intermittent power loss to the water pump control module. The water pump connector also had a loose communication line. Fix: Tightened ground point G107 to 8–10 N·m, repaired the LIN wiring inside the water pump connector, cleared the codes, and completed a 20 km road test with no recurrence.
Original source ↗
BYD DTC AI Analysis

e5 water pump power fuse holder burned, causing communication fault

✓
A BYD e5 (same thermal management platform as the Qin EV) could not fast charge. The dashboard displayed a thermal management fault, and the BMS stored DTC U014987. The LV battery management data stream showed abnormal thermal management water pump status. Inspection found burn damage on the 15A water pump fuse holder inside the front compartment distribution box. This caused pump supply voltage to fluctuate between 8-12V, below the LIN bus minimum operating voltage of 9V. Replaced the front compartment distribution box assembly, repaired the fuse holder contact surface, and confirmed stable 12V at the pump. Cleared the fault codes; fast charging returned to normal.
Original source ↗
BYD DTC AI Analysis

Burnt thermal management relay contacts caused water pump communication failure on Qin EV

✓
Qin EV displayed "Thermal Management System Fault" (DTC U014987) during cold start after sitting overnight. The fault appeared consistently at startup but cleared once warm. Multimeter measurement of the water pump supply voltage showed a drop below 6V during startup. Further inspection found burnt contacts on the thermal management water pump relay inside the front compartment fuse box. High inrush current during startup pulled the voltage down, resetting the water pump control module. Replaced the front compartment fuse box assembly, checked water pump operating current (normal: <8A), confirmed no abnormalities, and delivered the vehicle.
Original source ↗
BYD DTC AI Analysis

Seal 06 thermal management controller software defect caused water pump communication error

✓
A Seal 06 DM-i (thermal management architecture similar to the Qin EV) intermittently displayed thermal management warnings on the dashboard with reduced A/C cooling. Scanning showed fault code U014987 and related communication errors. The LIN bus termination resistance measured 45Ω (standard: 60Ω), causing signal reflection. Oscilloscope testing revealed waveform distortion. The battery thermal management controller had outdated software with a known protocol compatibility issue. Solution: Upgraded the thermal management controller to the latest software and added a 120Ω resistor in parallel at the LIN network end to match impedance. Cleared the fault codes and monitored for one week with no recurrence.
Original source ↗
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.