As a seasoned automotive technician specializing in hybrid and electric vehicles, I recently encountered a challenging case involving a 2024 BYD Han DM-i model, equipped with a BYD476ZQC engine and the BYD E-CVT-2 electro-hybrid system. This BYD car presented an intermittent issue where the vehicle failed to switch to EV mode despite having a high state of charge, causing the engine to remain active unnecessarily. Such problems in BYD EV systems can be perplexing due to their complex integration of electric and internal combustion components. In this article, I will delve into the diagnostic process, data analysis, and resolution of this fault, emphasizing the importance of systematic troubleshooting for modern BYD car technologies. Throughout this discussion, I will incorporate tables and mathematical formulas to summarize key findings and principles, aiding in a clearer understanding of the underlying mechanisms in BYD EV systems.
The initial complaint from the owner was that the BYD car occasionally refused to enter EV mode, even when the battery charge was sufficient. This was evident on the instrument panel, which displayed the engine running continuously, preventing the typical electric driving experience expected from a BYD EV. Upon connecting the VDS diagnostic tool to scan the vehicle’s systems, I retrieved a historical fault code: P230009, indicating an issue with the EV switch in the gear shift control assembly. Believing this to be the root cause, I replaced the gear shift control assembly unit. However, after two days of testing, the problem resurfaced without any new fault codes stored in the system. This highlighted the elusive nature of intermittent faults in BYD car models, necessitating a deeper investigation into the vehicle’s data streams and operational parameters.
To proceed, I focused on the data flow from the vehicle’s central controller, which revealed that the engine was being initiated due to an “ECVT cooling request.” This data pointed toward the electro-hybrid transmission system as the potential culprit. I verified the ECVT fluid level, inspected the cooling system for blockages, and ensured the radiator fans were functioning correctly—all of which appeared normal. This led me to conduct an extended road test with the customer’s BYD car left at the workshop. After approximately 30 kilometers of driving on a national highway, the fault manifested again: the vehicle remained stuck in HEV mode, with the engine running persistently and no energy regeneration occurring, even when shifting gears. At this point, I halted the BYD EV in a safe location to monitor real-time data, where I noticed an anomaly in the generator temperature reading.
The data stream from the central controller provided critical insights, particularly the temperature values for various components. For instance, the ECVT oil temperature was recorded at 85°C, the front motor temperature at 56°C, but the generator temperature soared to 103°C, which was significantly higher than expected. This discrepancy suggested an internal fault within the ECVT electro-hybrid system of the BYD car. To quantify this, I referred to the electrical schematics and performed resistance measurements on the temperature sensors. Specifically, I disconnected the ECVT system’s wiring harness and measured the resistance between pins AB72-2 and AB72-6 for the drive motor winding temperature, which read 27.29 kΩ. In contrast, the resistance between pins AB72-1 and AB72-5 for the generator winding temperature was only 4.74 kΩ. According to repair manuals for BYD EV systems, the expected resistance for motor windings at 20°C ambient temperature should range between 20 kΩ and 30 kΩ. The lower resistance for the generator indicated a potential short or degradation, correlating with the elevated temperature data.
This discovery underscored the importance of data-driven diagnostics in BYD car repairs. The relationship between temperature and resistance in electric motor windings can be described using the formula for temperature-dependent resistance, which is often approximated as: $$ R = R_0 [1 + \alpha (T – T_0)] $$ where \( R \) is the resistance at temperature \( T \), \( R_0 \) is the resistance at reference temperature \( T_0 \), and \( \alpha \) is the temperature coefficient of resistance. For copper windings commonly used in BYD EV motors, \( \alpha \) is approximately 0.00393 per °C. In this case, the measured resistance of 4.74 kΩ at an indicated temperature of 103°C deviated substantially from the expected range, suggesting an internal failure that disrupted the normal operation of the BYD car’s hybrid system.
To further illustrate the diagnostic data, I have compiled a table summarizing the key parameters observed during the fault occurrence. This table highlights the critical temperature and resistance values that guided the troubleshooting process for this BYD EV:
| Component | Temperature (°C) | Resistance (kΩ) | Expected Resistance at 20°C (kΩ) |
|---|---|---|---|
| ECVT Oil | 85 | N/A | N/A |
| Front Motor | 56 | 27.29 | 20-30 |
| Generator | 103 | 4.74 | 20-30 |
Based on this analysis, I concluded that the ECVT electro-hybrid system in the BYD car had internal damage, likely due to a faulty generator winding temperature sensor or related circuitry. This fault caused the system to misinterpret the generator’s thermal state, triggering unnecessary engine starts for cooling purposes and preventing the BYD EV from switching to electric mode. After replacing the affected ECVT component, I retested the vehicle over several days, confirming that the issue was resolved and the BYD car could seamlessly transition between EV and HEV modes as designed.
Reflecting on this case, it becomes evident that troubleshooting modern BYD EV systems requires a holistic approach, combining diagnostic tools, data interpretation, and an understanding of electro-thermal dynamics. The efficiency of a hybrid system like the BYD E-CVT-2 can be modeled using formulas such as the overall system efficiency \( \eta \), given by: $$ \eta = \frac{P_{\text{output}}}{P_{\text{input}}} \times 100\% $$ where \( P_{\text{output}} \) is the useful power delivered to the wheels, and \( P_{\text{input}} \) is the total power from the battery and engine. In this instance, the faulty generator increased losses, reducing efficiency and causing the observed symptoms. To prevent similar issues in BYD car models, regular monitoring of data streams—especially temperature-related parameters—is crucial. Below is another table summarizing preventive measures and key learning points for maintaining optimal performance in BYD EV systems:
| Aspect | Recommendation | Impact on BYD EV Performance |
|---|---|---|
| Data Stream Analysis | Regularly check temperature and resistance values during diagnostics | Early detection of anomalies, preventing mode-switching failures |
| Component Inspection | Verify sensor resistances against specifications | Ensures accurate thermal management in BYD car systems |
| System Testing | Conduct extended road tests to replicate intermittent faults | Identifies hidden issues not captured by fault codes |
In summary, this case of a BYD car with intermittent EV mode failure demonstrates the value of meticulous data analysis and adherence to technical specifications. By leveraging formulas like the temperature-resistance relationship and efficiency calculations, technicians can better diagnose and resolve complex issues in BYD EV platforms. As hybrid and electric vehicles evolve, such methodologies will become increasingly vital for ensuring reliability and customer satisfaction. The integration of advanced diagnostics with fundamental principles not only fixes immediate problems but also enhances the overall understanding of BYD car technologies, paving the way for more efficient and sustainable automotive solutions.