As an automotive technician specializing in electric vehicles, I recently encountered a challenging case involving a BYD EV model E5 from 2016, which had accumulated approximately 13,000 km in mileage. The customer reported an intermittent issue where the vehicle failed to achieve OK power status, accompanied by a dashboard warning prompting “Check Powertrain System.” This BYD car exhibited sporadic behavior, making diagnosis complex due to the non-recurring nature of the fault during initial inspection. In this article, I will detail my systematic approach to diagnosing and resolving this problem, emphasizing the importance of understanding the BYD EV’s high-voltage systems and utilizing precise measurements. The insights gained from this case can serve as a valuable reference for professionals working on similar BYD car models, highlighting common pitfalls in electric vehicle maintenance.
The BYD EV in question, a 2016 E5 model, is equipped with a sophisticated high-voltage architecture that includes components like the Battery Management System (BMS), motor controller (VTOG), and various sensors. The OK power status in this BYD car is critical for enabling the vehicle’s drive functions, and its activation depends on a seamless interaction between the BMS and VTOG. Specifically, during startup, the BMS initiates a pre-charge sequence to mitigate high-voltage surges. This involves the pre-charge contactor closing, allowing current to flow through a current-limiting resistor to the VTOG’s busbar. Once the busbar voltage reaches two-thirds of the battery pack’s rated voltage, the VTOG sends a pre-charge completion signal via CAN communication to the BMS, which then engages the main contactor and disengages the pre-charge contactor. Any disruption in this process can lead to the observed OK power failure in the BYD EV.
Upon connecting a diagnostic scanner to the BYD car, I retrieved two historical fault codes: P1A5A00, indicating a communication fault with the DC leakage sensor, and P1A6000, pointing to a high-voltage interlock loop (HVIL) fault. These codes were stored as historical data, and after clearing them, no active faults reappeared, suggesting an intermittent issue. Given the sporadic nature, I focused on potential causes such as faults in the DC leakage sensor circuitry, the sensor itself, CAN communication lines related to the sensor, HVIL component failures, or wiring issues within the HVIL circuit. This BYD EV’s design integrates these systems tightly, so a methodical check was essential.
To begin, I examined the DC leakage sensor, which is housed within the high-voltage electric control assembly (a four-in-one unit) in this BYD car. This sensor communicates via the powertrain CAN network and is connected to the BMS through “general leakage” and “severe leakage” signal lines. Using a multimeter, I measured voltages at the diagnostic port to assess CAN bus integrity. The results are summarized in the table below, confirming normal operation based on standard CAN voltage ranges for a BYD EV.
| Measurement Point | Expected Value (V) | Measured Value (V) | Status |
|---|---|---|---|
| G03/12 (CAN-H) to Ground | 2.5 – 2.7 | 2.69 | Normal |
| G03/13 (CAN-L) to Ground | 2.2 – 2.4 | 2.27 | Normal |
Next, I inspected the connector terminals for the DC leakage sensor, visually checking for anomalies such as corrosion or damage, but found none. Resistance measurements for the “general leakage” and “severe leakage” lines were performed to ensure continuity, as shown in the following table. All values were within specification, indicating no open or short circuits in this BYD EV’s wiring.
| Circuit Tested | Terminals Measured | Resistance (Ω) | Status |
|---|---|---|---|
| General Leakage | B28(B)/20 to BK45(A)/2 | < 1 | Normal |
| Severe Leakage | B28(B)/21 to BK45(A)/10 | < 1 | Normal |
Additionally, I used the diagnostic tool to read live data from the DC leakage sensor in this BYD car. The values for insulation resistance were consistently high, as expected for a properly functioning system. For instance, the “insulation resistance value” was 9,780 kΩ, “insulation resistance during detection” was 195 kΩ, and “post-detection insulation resistance” was 9,780 kΩ. These readings align with the formula for insulation integrity in a BYD EV, where the resistance should exceed a threshold to prevent leakage currents, often defined as $$ R_{\text{insulation}} > \frac{V_{\text{system}}}{I_{\text{leakage}}} $$ where \( V_{\text{system}} \) is the operating voltage and \( I_{\text{leakage}} \) is the maximum allowable leakage current. In this case, the data confirmed no faults in the DC leakage sensor or its associated circuits, leading me to shift focus to the HVIL system.
The high-voltage interlock loop in a BYD EV is a safety feature that ensures all high-voltage connectors are securely mated before enabling the powertrain. A break in this loop can cause intermittent OK power failures. I accessed the HVIL data stream via the diagnostic tool, which showed parameters like “discharge allowed: yes,” “charge allowed: yes,” and “HVIL status: unlocked” for all segments, suggesting no active faults. However, given the historical code and intermittent nature, I suspected a loose connection in the HVIL circuit. The HVIL in this BYD car forms a continuous loop through multiple connectors, and any gap can trigger a fault. To quantify this, I performed resistance measurements across key points in the HVIL pathway, as detailed in the table below.
| Measurement Segment | Terminals Measured | Resistance (Ω) | Status |
|---|---|---|---|
| Segment 1 | B28(B)/22 to B52/2 | < 1 | Normal |
| Segment 2 | B52/1 to BK45(A)/1 | < 1 | Normal |
| Segment 3 | BK45(B)/7 to KxK51/30 | < 1 | Normal |
| Segment 4 | KxK51/29 to B28(B)/23 | < 1 | Abnormal (gap observed) |
During the resistance check for the segment between KxK51/29 and B28(B)/23, I noted that the terminal B28(B)/23 had an excessive gap, which could cause intermittent disconnections. This finding was critical, as it explained the sporadic nature of the fault in this BYD EV. To verify, I reassembled the circuit and simulated real-world conditions by gently wiggling the connector while monitoring the OK power status. The vehicle repeatedly cycled between losing and regaining OK power, eventually settling into a persistent failure mode. This confirmed that the loose terminal was the root cause, disrupting the HVIL and preventing the BYD car from achieving a stable pre-charge state.
The pre-charge process in a BYD EV can be modeled mathematically to understand the voltage thresholds involved. For instance, the pre-charge voltage condition is defined as $$ V_{\text{precharge}} = \frac{2}{3} \times V_{\text{battery}} $$ where \( V_{\text{battery}} \) is the nominal voltage of the battery pack. In this BYD car, if the HVIL is broken, the BMS may not initiate pre-charge, leading to a failure in meeting this condition. The resistance measurements I conducted can be related to Ohm’s law, $$ V = I \times R $$ where any increase in resistance due to poor connections could cause voltage drops, affecting sensor readings. Although my measurements showed low resistance, the intermittent gap introduced a variable resistance that only manifested under certain conditions, highlighting the importance of physical inspection in BYD EV diagnostics.
After identifying the faulty terminal B28(B)/23, I proceeded to adjust its gap to restore proper contact. This involved carefully bending the terminal pin to ensure a snug fit within the connector. Once corrected, I test-drove the BYD car extensively, including on various road surfaces to simulate vibrations that might trigger the fault. The OK power status remained stable throughout, and no warning messages reappeared. This successful resolution underscores how subtle mechanical issues, such as terminal gaps, can lead to significant electrical faults in a BYD EV. In this case, the customer mentioned that the vehicle had been involved in an accident around 10,000 km, during which the HVIL might have been improperly handled, leading to the terminal deformation. This experience reinforces the need for meticulous inspections after any repairs on a BYD car, especially involving high-voltage systems.
In summary, diagnosing intermittent faults in a BYD EV requires a holistic approach that combines code reading, data stream analysis, and physical checks. The use of multimeter measurements and diagnostic tools is essential, but as seen in this BYD car, visual inspection of connectors can be equally important. The table below recaps the key diagnostic steps and outcomes, emphasizing the iterative process used to isolate the fault in this BYD EV.
| Diagnostic Step | Tool/Method Used | Observation | Conclusion |
|---|---|---|---|
| Initial Code Scan | Diagnostic Scanner | Historical codes P1A5A00 and P1A6000 | Intermittent fault suspected |
| DC Leakage Sensor Check | Multimeter and Data Stream | Normal voltages and resistances | Sensor and circuits ruled out |
| HVIL Circuit Inspection | Resistance Measurements | Low resistance but terminal gap found | Fault localized to B28(B)/23 |
| Verification Test | Physical Manipulation | OK power fluctuated with connector movement | Root cause confirmed |
Furthermore, the principles of high-voltage system integrity in a BYD EV can be generalized using formulas for reliability. For example, the probability of an intermittent fault occurring might be expressed as $$ P_{\text{fault}} = 1 – e^{-\lambda t} $$ where \( \lambda \) is the failure rate and \( t \) is time, but in practice, it often boils down to physical connections. This case with the BYD car demonstrates that even minor oversights during maintenance can escalate into recurring issues. As electric vehicles like the BYD EV evolve, technicians must prioritize connector integrity and follow standardized procedures to avoid such pitfalls. Ultimately, this diagnosis not only resolved the immediate problem but also provided a learning opportunity for handling similar cases in other BYD car models, ensuring safer and more reliable operation.