As a certified technician specializing in electric vehicles, I recently encountered a challenging case involving a BYD EV that presented intermittent power system failures. This BYD car, a 2024 model with advanced blade battery technology and an integrated high-voltage system, had accumulated approximately 6,000 km. The owner reported occasional power limitations accompanied by a “Power System Failure” alert on the dashboard, particularly during rainy conditions. This issue would resolve itself after a day or two of dry weather, making it a perplexing intermittent fault. In this detailed account, I will walk through the diagnostic process, leveraging my expertise with BYD EV systems, and incorporate key data through tables and formulas to elucidate the findings.
The initial step involved verifying the fault. Upon receiving the BYD car, I performed a standard startup procedure: depressing the brake pedal and activating the start switch. The dashboard’s “OK” light illuminated normally without any warnings. Using BYD’s proprietary diagnostic tool, the Vehicle Diagnostic System (VDS), I scanned for fault codes and retrieved historical codes related to high-voltage system leakage. These codes were clearable, indicating a transient issue. Communicating with the owner revealed a pattern: the fault consistently occurred during rainy drives and subsided in sunny weather. This correlation suggested that moisture infiltration into the high-voltage system might be triggering leakage faults, leading to power limitations. A test drive under dry conditions showed normal acceleration and no alerts, so I returned the BYD EV to the owner with instructions to report back immediately if the issue recurred.
Two weeks later, during a rainy day, the owner notified me that the “Power System Failure” alert had reappeared. The vehicle remained operational but exhibited reduced acceleration. I advised the owner to bring the BYD car to the service center safely. Upon arrival, the alert persisted. A subsequent VDS scan revealed current fault code “P1A0100 General electric leakage” and historical code “P1A0000 Serious electric leakage” stored in the Battery Management System (BMS). With the fault active, I proceeded to investigate using standard high-voltage leakage detection methods for BYD EV models.
Given that the leakage codes were stored in the BMS, and the high-voltage components are interconnected, I needed to isolate whether the leakage originated from the battery pack or external parts. Referring to BYD’s “3+3” platform high-voltage system framework, I donned appropriate insulating gear and executed a high-voltage power-down. At the battery pack end, I disconnected the high-voltage DC busbars and inspected the connections; the waterproof seals appeared intact, with no signs of moisture. Using a megohmmeter, I measured the insulation resistance between the positive and negative high-voltage DC busbars and the shielding layer (vehicle chassis ground). Both readings were infinite, indicating no leakage in the non-battery high-voltage sections. This pointed toward a potential internal leakage within the battery pack of the BYD EV.
To confirm internal battery pack leakage, further insulation testing was necessary. However, direct measurement with a megohmmeter was not feasible due to the internal placement of the main positive and negative contactors in the blade battery. According to the national standard GB 18384-2020 for electric vehicle safety, BYD has defined specific insulation criteria for their high-voltage systems. The insulation resistance is calculated as the ratio of measured resistance to system voltage, and the standards are summarized in the table below:
| Insulation Resistance (Ω/V) | Status |
|---|---|
| ≥ 500 | No Leakage |
| 100 ≤ R < 500 | General Leakage |
| < 100 | Serious Leakage |
With the battery pack’s high-voltage DC busbars disconnected, I reconnected the low-voltage battery’s negative terminal and powered on the vehicle. Connecting the VDS, I accessed BMS data streams and recorded a total battery voltage of 299 V. Entering maintenance mode, I used the VDS to measure the internal insulation resistance of the battery pack, which read 61 kΩ. The insulation resistance per volt can be calculated using the formula:
$$ R_{\text{ins}} = \frac{R_{\text{meas}}}{V} $$
where \( R_{\text{meas}} \) is the measured resistance and \( V \) is the voltage. Substituting the values:
$$ R_{\text{ins}} = \frac{61,000 \, \Omega}{299 \, \text{V}} \approx 204 \, \Omega/\text{V} $$
This result, 204 Ω/V, falls within the “General Leakage” range according to BYD’s standards, consistent with the current fault code P1A0100. Thus, I concluded that the battery pack internal leakage was the root cause in this BYD car.
Considering the owner’s feedback that faults occurred predominantly in rainy weather, I suspected compromised battery pack seals allowing water ingress. Upon lifting the vehicle, I observed significant impact-induced凹陷 on the battery pack underside, with the deepest point measuring nearly 7 mm. This damage likely caused cracks in the cell tray, permitting rainwater entry and triggering leakage faults. Since blade batteries are not serviceable, replacement was necessary. After installing a new battery pack, I rechecked the internal insulation resistance, which exceeded 500 Ω/V. Multiple road tests under various conditions, including simulated rain, confirmed no recurrence of faults. Follow-ups with the owner during rainy periods affirmed normal operation without alerts, validating the repair.
The diagnostic process for this BYD EV highlighted the importance of systematic insulation testing and environmental factors in electric vehicle maintenance. To further illustrate the insulation resistance calculations and their implications, I have compiled key formulas and data in the following sections. These elements are crucial for technicians working on BYD EV models to ensure accurate fault isolation and repair.
Insulation resistance is a critical parameter in high-voltage systems of BYD cars, as it directly impacts safety and performance. The general formula for insulation resistance per volt is:
$$ R_{\text{ins}} = \frac{R_{\text{total}}}{V_{\text{system}}} $$
where \( R_{\text{total}} \) is the total insulation resistance measured in ohms, and \( V_{\text{system}} \) is the system voltage in volts. For instance, in this BYD EV case, with \( R_{\text{total}} = 61,000 \, \Omega \) and \( V_{\text{system}} = 299 \, \text{V} \), the calculation aligns with BYD’s leakage thresholds. Repeated testing under different conditions can help monitor degradation; for example, if a BYD car exhibits insulation values below 100 Ω/V, immediate action is required to prevent serious faults.
In addition to formulas, tabulating common fault codes and their interpretations aids in efficient diagnosis. Below is a table summarizing typical BMS fault codes in BYD EV systems related to leakage, based on my experience:
| Fault Code | Description | Implication |
|---|---|---|
| P1A0000 | Serious Electric Leakage | Insulation resistance < 100 Ω/V; requires urgent inspection |
| P1A0100 | General Electric Leakage | 100 Ω/V ≤ R < 500 Ω/V; indicates potential moisture issues |
| Other codes | Various system errors | May relate to sensors or connectors in BYD EV high-voltage network |
Furthermore, the integration of high-voltage components in BYD EV designs, such as the “3+3” system, necessitates a holistic approach to troubleshooting. The overall insulation resistance of the system can be modeled as a parallel combination of resistances from individual components. For a system with multiple high-voltage parts, the total insulation resistance \( R_{\text{total}} \) is given by:
$$ \frac{1}{R_{\text{total}}} = \frac{1}{R_1} + \frac{1}{R_2} + \cdots + \frac{1}{R_n} $$
where \( R_1, R_2, \ldots, R_n \) represent the insulation resistances of each component. In practice, for a BYD car, this means that even a small leakage in one part, like the battery pack, can significantly reduce the overall resistance, triggering faults. During my diagnosis, by isolating the battery pack, I simplified this to \( R_{\text{total}} = R_{\text{battery}} \), confirming the source.
Preventive maintenance for BYD EV models should include regular insulation checks, especially after exposure to harsh conditions. The recommended insulation resistance for a healthy BYD EV high-voltage system is derived from the standard:
$$ R_{\text{min}} = 500 \times V_{\text{system}} $$
For a typical BYD car with a system voltage of 300 V, this translates to \( R_{\text{min}} = 150,000 \, \Omega \) or 150 kΩ. Values below this threshold warrant investigation. In this case, the measured 61 kΩ was substantially lower, indicating degradation. Additionally, environmental factors like humidity can affect readings; thus, I often use correction factors in calculations. For example, the adjusted insulation resistance \( R_{\text{adj}} \) might be estimated as:
$$ R_{\text{adj}} = R_{\text{meas}} \times k_h $$
where \( k_h \) is a humidity-dependent factor, typically ranging from 0.8 to 1.2 for BYD EV systems in varying climates.
In conclusion, diagnosing and resolving power system failures in BYD EV units requires a methodical approach, combining diagnostic tools, insulation testing, and environmental analysis. The use of formulas and tables, as demonstrated, streamlines the process and enhances accuracy. For this BYD car, replacing the battery pack resolved the issue, but ongoing monitoring is essential to prevent recurrences. As electric vehicles evolve, techniques like these will remain vital for maintaining the reliability and safety of BYD EV fleets worldwide.