As an automotive technician specializing in electric vehicles, I recently encountered a challenging case involving a BYD EV model that failed to charge via AC power. The vehicle, a BYD car with approximately 50,000 km on the odometer, was brought in with customer complaints of inability to initiate AC charging. This BYD EV is known for its reliability, so I approached the diagnosis systematically to identify the root cause. In this article, I will detail the entire diagnostic process, from initial inspection to final resolution, focusing on the AC charging system of the BYD car. Throughout, I will emphasize the importance of understanding circuit principles and using precise measurements, while incorporating tables and formulas to summarize key points. The goal is to provide a comprehensive guide for professionals working on similar BYD EV models.
Upon receiving the BYD EV, I first performed a preliminary test to verify the customer’s report. I connected an AC charging gun to the vehicle’s port and observed that the charging indicator did not illuminate, and the system showed no signs of activation. This confirmed the fault: the BYD car was indeed unable to charge using AC power. Using a diagnostic scanner, I read the fault codes from the vehicle’s onboard systems. Surprisingly, no fault codes were stored, which often complicates diagnostics. Next, I accessed the data stream from the charging and distribution unit, a critical component in BYD EV models. The data indicated a “charging pause” status, while the charging connection device showed “standard gun connected,” suggesting that the CC (Control Pilot) signal was functional. However, further analysis was needed to pinpoint the issue. The initial data stream readings are summarized in the table below, which highlights key parameters relevant to the BYD EV’s charging system.
| Parameter | Value | Interpretation |
|---|---|---|
| Charging System Status | Charging Pause | Indicates interruption in charging process |
| Connection State | Standard Gun Connected | CC line appears normal |
| CP Signal Voltage | Abnormal (measured later) | Key to diagnosing fault |
To proceed, I needed a deep understanding of the AC charging control circuit in BYD EV vehicles. The principle involves multiple detection points that communicate between the vehicle and the charging infrastructure. In a BYD car, the AC charging system relies on resistors and voltage dividers to manage signals. Detection point 3 monitors the connection between the vehicle plug and socket via the CC line. When disconnected, the resistance between CC and PE (Protective Earth) is infinite; when partially connected, it equals $R_C + R_4$; and when fully connected, it simplifies to $R_C$. This resistance variation translates into voltage changes, allowing the system to detect connection status. The voltage at detection point 3 can be modeled using Ohm’s law: $$V_3 = I \times R_{eq}$$ where $R_{eq}$ is the equivalent resistance in the circuit.
Detection point 2 assesses whether the charging connection device is fully engaged. In a properly functioning BYD EV, when the power supply equipment is operational and the interface is connected, switch S1 transitions from a 12 V state to a PWM (Pulse Width Modulation) state. This change alters the voltage due to series resistors $R_1$ and $R_3$, resulting in a PWM signal shift from 12 V to 9 V. The voltage here can be expressed as: $$V_2 = V_{source} \times \frac{R_3}{R_1 + R_3}$$ where $V_{source}$ is the initial voltage. Detection point 1 confirms vehicle readiness by closing switch S2, which parallels $R_3$ with $R_2$, further dividing the voltage and changing the PWM signal to 6 V. The formula for this scenario is: $$V_1 = V_{source} \times \frac{R_3 \parallel R_2}{R_1 + (R_3 \parallel R_2)}$$ where $R_3 \parallel R_2$ denotes the parallel resistance. If any of these signals deviate, the BYD EV may halt charging, as observed in this case.
After reviewing the theory, I examined the specific AC charging circuit of this BYD car. The circuit involves multiple connectors and wires, with the CP (Control Pilot) line playing a pivotal role in communication. Potential causes for the charging failure in this BYD EV included faults in the CP line, issues with the charging and distribution unit, or problems at the AC charging port itself. To narrow it down, I used an oscilloscope to measure the waveform at terminal BK46/5 relative to ground. The reading showed a constant 3.2 V line, which was abnormal; in a healthy BYD EV, the CP signal should exhibit a PWM waveform with variations between 6 V and 12 V, as illustrated in standard diagrams. Similarly, measuring at the AC charging port terminal KB53B/1 revealed a steady 10.8 V line, further indicating an anomaly. This suggested a possible discontinuity or high resistance in the CP line between terminals BK46/5 and KB53B/1.
I then proceeded with resistance measurements using a multimeter to isolate the fault. Disconnecting connectors BK46 and KB53B, I measured the resistance between terminals BK46/5 and KB53B/1. The value was 8.03 kΩ, significantly higher than the expected less than 1 Ω for a proper connection in a BYD EV. Next, I disconnected connector KJB01 and measured between KB53B/1 and KJB01/2, obtaining a normal 0.4 Ω. However, the resistance between BK46/5 and BJK01/2 was 8.0 kΩ, confirming a virtual open circuit in this segment. This high resistance explained why the CP signal was compromised: the elevated resistance prevented the PWM signal from transitioning correctly, leading the power control unit to interpret the vehicle as not ready, thus pausing the charge. The following table summarizes these measurements, emphasizing the critical values for the BYD car’s diagnosis.
| Measurement Point | Resistance Value | Normal Range | Status |
|---|---|---|---|
| BK46/5 to KB53B/1 | 8.03 kΩ | < 1 Ω | Abnormal |
| KB53B/1 to KJB01/2 | 0.4 Ω | < 1 Ω | Normal |
| BK46/5 to BJK01/2 | 8.0 kΩ | < 1 Ω | Abnormal |
Based on these findings, I concluded that the CP line between terminals BK46/5 and BJK01/2 in this BYD EV had a virtual connection, causing excessive resistance. This fault disrupted the CP signal’s integrity, which is essential for the charging handshake in a BYD car. The power control unit could not detect the vehicle’s readiness due to the distorted PWM signal, resulting in the charging pause. To resolve this, I ordered a replacement harness based on the vehicle’s chassis number. After installing the new wiring and reassembling the components, I tested the BYD EV again. The AC charging initiated smoothly, and the data stream showed normal operation, confirming that the issue was fixed.
In summary, this case underscores the importance of meticulous circuit analysis when dealing with charging failures in BYD EV models. The CP line’s role in facilitating communication between the vehicle and charger cannot be overstated; even minor resistances can lead to significant malfunctions. For technicians working on BYD cars, using tools like oscilloscopes and multimeters to measure waveforms and resistances is crucial. Additionally, understanding the underlying formulas, such as those for voltage division in PWM signals, can aid in diagnosing similar issues. This experience with the BYD EV has reinforced my approach to electric vehicle diagnostics, highlighting the need for systematic testing and a firm grasp of electronic principles. As the adoption of BYD EV vehicles grows, such insights will become increasingly valuable for maintaining their performance and reliability.
To further elaborate on the diagnostic process, let me discuss the broader implications for BYD EV charging systems. The AC charging mechanism in a BYD car involves a complex interplay of signals, and any deviation can trigger safety protocols that pause charging. In this instance, the high resistance in the CP line effectively mimicked an open circuit, preventing the necessary voltage drops that indicate vehicle readiness. The general equation for the PWM signal voltage in a BYD EV can be derived from the resistor network: $$V_{PWM} = V_{ref} \times \frac{R_{parallel}}{R_{series} + R_{parallel}}$$ where $V_{ref}$ is the reference voltage, $R_{series}$ is the series resistance, and $R_{parallel}$ is the equivalent parallel resistance in the detection points. When resistances exceed tolerances, as in this BYD car, $V_{PWM}$ fails to reach thresholds, causing malfunctions.
In future cases involving BYD EV models, I recommend starting with data stream analysis to identify anomalies, followed by physical measurements of key signals. Creating a checklist for common faults in BYD cars, such as CP line issues or connector corrosion, can streamline diagnostics. Moreover, regular maintenance of the charging ports and wiring harnesses in BYD EV vehicles can prevent such failures. This case not only resolved the immediate problem but also provided valuable insights into the robustness of BYD EV systems, demonstrating how detailed electrical knowledge can lead to efficient repairs. As electric vehicles like the BYD car evolve, continuous learning and adaptation will be essential for technicians to keep pace with advancing technologies.