As an automotive technician specializing in electric vehicles, I recently encountered a challenging case involving a BYD EV model, specifically a 2023 BYD car from the Qin PLUS EV Champion series. This BYD EV was equipped with a 100kW permanent magnet front motor and an advanced heat pump air conditioning system. The owner reported that the air conditioning was not cooling properly, and the airflow direction could not be adjusted despite changes shown on the multimedia display. No fault indicators appeared on the instrument cluster, which made this an intriguing diagnostic puzzle. In this article, I will detail the step-by-step process I followed to identify and resolve the issue, emphasizing the importance of understanding modern BYD car systems. Throughout, I will incorporate tables and formulas to summarize key points, ensuring a comprehensive analysis of this BYD EV fault.
Upon initial inspection of the BYD EV, I confirmed the owner’s complaints: the air conditioning system failed to produce cold air, and the vent direction remained static even when adjusted via the multimedia interface. This BYD car exhibited no obvious signs of damage or wear, so I proceeded with a systematic diagnostic approach. Using the BYD-specific diagnostic tool VDS2100, I performed a full module scan of the vehicle. The scan revealed multiple current fault codes stored in the right body domain controller, all related to the HVAC system. These included errors such as mode motor rotation failure, internal ECU faults, and refrigerant temperature sensor shorts. Notably, these codes could not be cleared, indicating a persistent hardware or wiring issue in this BYD EV.
The heat pump air conditioning system in this BYD car is a sophisticated setup that uses refrigerant as a medium to transfer heat. In cooling mode, it moves heat from the passenger compartment to the outside; in heating mode, it draws heat from the environment or vehicle waste heat into the cabin. This system supports various functions, including air conditioning, battery heating and cooling, and dehumidification, all controlled by the right body domain controller. The controller integrates sensors and actuators like the electric compressor, high-voltage PTC, flap motors, electronic expansion valves, and fans. For a BYD EV, this design simplifies refrigerant管路布局 but increases complexity in diagnostics. To understand the fault, I considered potential causes: software glitches, motor failures, controller defects, or wiring problems. Given the multiple fault codes, I hypothesized that a common point of failure, such as a shared circuit or ground, might be affecting multiple components in this BYD car.
First, I verified that all system software in the BYD EV was up-to-date using the VDS2100 tool. After confirming no software issues, I attempted to forcibly reprogram the right body domain controller, but the faults persisted. This ruled out software-related problems and shifted focus to hardware. I then examined the circuit diagrams for this BYD car model, which showed that various mode motors, sensors, and actuators are controlled by the right body domain controller but not necessarily through common fuses or ground points. This suggested a possible wiring short that could disrupt multiple systems. I used a multimeter to measure resistances of motors like the mode and blend door actuators; all readings were within normal ranges, and power supplies were stable. Disconnecting individual components one by one did not resolve the issue, reinforcing that the problem might lie in the wiring harness.
Further investigation involved physically manipulating the wiring harness in the BYD EV’s front compartment, near the compressor area. When I shook the harness, the air conditioning temporarily resumed normal function, pointing to an intermittent short. Upon closer inspection, I found that a branch of the front drive unit harness had rubbed against the compressor mounting bracket, causing insulation wear and exposing wires. The damaged section included lines for the air conditioning pressure sensor, which shares a junction with other sensors. This short to ground likely triggered cascading faults in other sensors, prompting the right body domain controller to enter a protective mode that disabled motor adjustments. In a BYD car, such issues can stem from improper harness routing during assembly. According to service guidelines, the harness tie should be positioned at least 30±5 mm from protective外壳 to prevent contact with fixed brackets. In this case, the distance was only about 20 mm, leading to interference and abrasion.
To resolve the fault in this BYD EV, I repaired the damaged wires by splicing and insulating them properly. I then adjusted the harness tie position to maintain the recommended 30 mm clearance from the protective外壳 and secured the branch harness above the main loom to prevent future contact. After reassembly, I tested the system: the air conditioning cooled effectively, and vent direction changes responded correctly. All fault codes were cleared, and subsequent scans showed no errors, confirming a successful repair. This case highlights how minor manufacturing deviations can cause significant failures in a BYD car, emphasizing the need for meticulous inspections.
Reflecting on this diagnostic journey, I realized that troubleshooting modern BYD EV systems requires a deep understanding of their design principles and control logic. The heat pump system in a BYD car, for instance, relies on precise sensor inputs to regulate refrigerant flow and temperature. A general formula for heat pump efficiency is the Coefficient of Performance (COP), given by $$ \text{COP} = \frac{Q_c}{W} $$ where \( Q_c \) is the cooling capacity and \( W \) is the work input. In this BYD EV, faults in sensors like the pressure or temperature units can skew calculations, leading to system shutdowns. Additionally, Ohm’s law, $$ V = I \times R $$, where \( V \) is voltage, \( I \) is current, and \( R \) is resistance, proved useful in testing motor integrity. For example, measuring resistance helped verify that motors were not shorted or open-circuited, common issues in BYD car HVAC systems.
To summarize the diagnostic steps, I have compiled key data into tables below. These tables outline the fault codes, component checks, and repair actions, providing a clear reference for similar cases in BYD EV models.
| Fault Code | Description | Status |
|---|---|---|
| B2A2A92 | Mode Motor Rotation Not Achieved | Current |
| B134413 | ECU Internal Fault | Current |
| B134611 | Compressor Outlet Refrigerant Temperature Sensor T1 Short to Ground | Current |
This table illustrates the range of errors that can occur in a BYD car’s HVAC system, often interlinked through shared circuits. For instance, a short in one sensor can propagate faults to others, as seen in this BYD EV.
| Step | Action | Observation | Conclusion |
|---|---|---|---|
| 1 | Full module scan with VDS2100 | Multiple current fault codes in right body domain controller | Hardware or wiring issue likely |
| 2 | Software update and reprogramming | Faults persisted after reset | Software ruled out |
| 3 | Resistance measurement of motors | All values within normal range (e.g., 10-50 Ω for typical motors) | Motors not faulty |
| 4 | Harness manipulation test | AC function restored temporarily when harness shaken | Intermittent short identified |
| 5 | Visual inspection of harness | Abrasion found near compressor bracket, wires exposed | Root cause: wiring short to ground |
This diagnostic table underscores the importance of a methodical approach in BYD EV repairs. By eliminating possibilities step by step, I narrowed down the fault to a specific wiring issue, which is common in densely packed BYD car engine bays.
In terms of technical insights, the heat pump system in a BYD EV operates based on thermodynamic principles. The cooling capacity \( Q_c \) can be expressed as $$ Q_c = \dot{m} \cdot \Delta h $$ where \( \dot{m} \) is the mass flow rate of refrigerant and \( \Delta h \) is the enthalpy change across the evaporator. If sensors like the pressure or temperature units fail, the controller cannot calculate these values accurately, leading to malfunctions. For this BYD car, the pressure sensor’s output voltage \( V_{\text{sensor}} \) relates to pressure \( P \) by a linear approximation $$ V_{\text{sensor}} = k \cdot P + C $$ where \( k \) is a constant and \( C \) is an offset. A short to ground would force \( V_{\text{sensor}} \) to zero, causing erroneous readings and system shutdown.
Preventive measures for such issues in BYD EV models include regular inspections of wire routing and adherence to assembly specifications. The formula for minimum clearance \( d_{\text{min}} \) between harness and fixed parts is $$ d_{\text{min}} = 30 \pm 5 \text{ mm} $$ as per BYD guidelines. In this case, non-compliance led to the fault, highlighting the need for quality control in BYD car production. Additionally, using diagnostic tools to monitor live data, such as sensor voltages and motor positions, can preempt failures. For example, if a mode motor’s position feedback deviates from expected values, it might indicate an impending fault in a BYD EV.
In conclusion, diagnosing and fixing the HVAC failure in this BYD EV required a blend of theoretical knowledge and practical skills. The integration of advanced systems in modern BYD cars demands continuous learning and adaptation from technicians. By sharing this experience, I hope to emphasize the value of thorough diagnostics and the role of detailed circuit analysis in maintaining BYD EV reliability. As electric vehicles evolve, staying updated with technologies like heat pumps and domain controllers will be crucial for addressing similar challenges in future BYD car models.