As an automotive repair technician specializing in electric vehicles, I recently encountered a challenging case involving a BYD car, specifically a 2018 BYD Tang DM model. This BYD EV, equipped with a BYD487ZQA engine and a 3.3kW onboard charger, presented an unusual issue where the charging power was limited to only 1.5kW when using standard 3.3kW or 7kW AC charging stations. The vehicle lacked DC charging capability, making this AC charging problem critical for the owner’s daily use. In this detailed account, I will walk through the diagnostic process, share insights into BYD EV systems, and highlight how we resolved the issue, emphasizing the importance of thorough electrical checks in modern BYD car maintenance.
The customer reported that during charging, the dashboard consistently displayed a charging power of 1.5kW, which was significantly lower than the expected 3.3kW. This BYD EV had a relatively low mileage of around 11,076 km, and initial scans revealed no fault codes in the system. As a technician, I knew that such power limitations in a BYD car could stem from various factors, including signal abnormalities, lock mechanisms, or thermal issues. To begin, I connected the diagnostic tool to retrieve data streams from the onboard charger. The readings appeared normal, with no obvious anomalies in voltage or current parameters. For instance, the PWM duty cycle for the control pilot (CP) signal was measured at 55%, which falls within the standard range for BYD EV charging systems. Similarly, the CC resistance was around 687 ohms, indicating a proper connection between the charging gun and the vehicle.
Next, I focused on the AC charging port’s electronic lock. In BYD EV models, if this lock fails to engage, it can trigger a power limitation as a safety measure. Upon inspection, the lock was functioning correctly, and the dashboard showed no warnings related to it. This ruled out one potential cause. I then checked the battery pack temperature through the battery management system. The data indicated that the highest and lowest cell temperatures were around 30°C, which is well within the normal operating range for a BYD car. Thermal issues are common culprits in charging problems, as excessive heat can force the system to reduce power output. For example, if the charging port temperature exceeds 75°C, the BYD EV may limit power, and at 85°C, it could shut down charging entirely. However, in this case, the temperatures were stable.
Moving forward, I examined the onboard charger itself. Located in the rear compartment, this component is crucial for converting AC power to DC for the battery. I noted that the cooling fan was operating smoothly, and there were no signs of overheating. To eliminate the possibility of a faulty charger, I swapped it with a known good unit from another BYD EV. Surprisingly, the issue persisted, indicating that the problem lay elsewhere in the system. This was a turning point in the diagnosis, as it shifted our focus to the power supply circuits. The customer mentioned that the onboard charger had been replaced recently due to a previous failure, and the old unit had a burnt smell. This history suggested that an electrical fault might have damaged related components.
Upon reviewing the wiring diagrams for this BYD car, I identified that the onboard charger receives power from two sources: a constant live feed and an ignition-switched (IG1) feed. These are protected by fuses in the rear distribution box. Specifically, the constant power fuse was labeled F8/10 (20A), and the IG1 fuse was F8/29 (7.5A). Using a multimeter, I tested these fuses and found that F8/29 had blown, showing infinite resistance. This meant that the IG1 circuit was interrupted, likely causing the onboard charger to operate in a limited mode. I then checked for short circuits by measuring the resistance between the fuse terminals and the chassis; it read approximately 1kΩ, indicating no direct short. Replacing the fuse resolved the issue immediately, and subsequent charging tests showed the power restored to over 3kW, as expected for this BYD EV.
This case underscores the complexity of diagnosing BYD EV charging systems. To summarize key points, I’ve compiled tables and formulas that highlight critical aspects of such faults. For instance, the charging power in a BYD car can be calculated using the basic formula for AC power: $$P = V \times I \times \text{Power Factor}$$ where P is power in watts, V is voltage, I is current, and the power factor accounts for efficiency. In this scenario, the limited power of 1.5kW might relate to reduced current due to the fuse failure. Additionally, the PWM duty cycle plays a role in communication between the charger and BYD EV; it can be expressed as: $$\text{Duty Cycle} = \frac{\text{Pulse Width}}{\text{Period}} \times 100\%$$ A normal duty cycle of around 55% ensures proper signal transmission, as seen in this case.
| Cause | Description | Typical Symptoms |
|---|---|---|
| CC or CP Signal Anomalies | Issues with resistance or PWM signals from charging station | Reduced power, no fault codes |
| AC Electronic Lock Failure | Lock not engaging properly during charging | Dashboard warnings, power limitation |
| Battery Temperature Issues | High or low cell temperatures triggering safety limits | Gradual power reduction, thermal warnings |
| Onboard Charger Faults | Internal failures or power supply problems | Burnt smells, inconsistent charging |
| Fuse or Circuit Breaks | Blown fuses in distribution boxes | Sudden power drops, no obvious faults |
Another important aspect is the thermal management in BYD EV charging. For example, if the charging port temperature sensor reads abnormally, such as -40°C, it might indicate an open or short circuit, leading to half-power charging. In 3kW charging setups, the BYD car may not monitor port temperature, defaulting to -40°C in data streams without action. However, for higher power levels, temperature thresholds are critical. The cooling system also plays a role; if the coolant temperature exceeds 65°C, the BYD EV begins to reduce charging current by 2A per degree, and it stops entirely above 85°C. These strategies are platform-specific and may evolve, but they highlight the need for comprehensive checks in any BYD car diagnosis.
| Component | Temperature Range | System Response |
|---|---|---|
| Charging Port | Below 75°C | Normal charging |
| Charging Port | 75°C to 85°C | Limited power charging |
| Charging Port | Above 85°C | Charging stopped |
| Coolant Circuit | Above 65°C | Current reduction by 2A/°C |
| Coolant Circuit | Above 85°C | Charging terminated |
In this particular BYD EV, the fuse failure was likely a residual effect from the previous charger replacement. When the onboard charger shorted internally, it could have caused a surge that blew the IG1 fuse. This emphasizes the importance of verifying all power circuits after component swaps in a BYD car. To prevent recurrence, I advised the customer on regular maintenance checks, such as inspecting fuses and ensuring proper cooling system function. The restored charging power not only improved the vehicle’s usability but also demonstrated the resilience of BYD EV designs when properly maintained.
Reflecting on this experience, I realize that diagnosing BYD EV issues requires a methodical approach. Starting with simple checks like fuse integrity can save time and resources. For example, the resistance measurement for the CC circuit should ideally match standards, such as 680 ohms for a fully connected state. Using Ohm’s law, $$V = I \times R$$, we can relate voltage drops to potential issues. In this BYD car, the multimeter readings confirmed the circuit was intact, guiding us to the fuse. Moreover, data log analysis is crucial; by monitoring parameters like PWM and temperature over time, technicians can identify patterns that point to underlying faults. This case also highlights the value of customer history; without the input on the previous charger failure, we might have overlooked the fuse entirely.
In conclusion, working on this BYD EV taught me valuable lessons about electric vehicle diagnostics. The integration of advanced systems in BYD car models demands a deep understanding of both hardware and software. By sharing this account, I hope to assist other technicians facing similar challenges with BYD EV charging limitations. Remember, even minor components like fuses can have major impacts, and a comprehensive diagnostic strategy is key to efficient repairs. As the adoption of BYD EV and other electric vehicles grows, such insights will become increasingly important in the automotive repair industry.