As a technician specializing in BYD EV models, I recently encountered a case involving a BYD car that failed to charge via slow charging. The owner reported that during the last charging attempt, the instrument panel displayed only a connector icon without any additional information, such as charging status, power, or estimated time to full charge. Normally, the BYD EV should show “charging in progress” along with relevant data. This issue prevented the BYD car from initiating the charging process, indicating a potential fault in the charging system.
To address this, I began by examining the slow charging principles for the BYD EV. The AC slow charging system involves multiple stages of signal exchange between the charging pile and the vehicle. Key components include the charging gun, vehicle charging port, onboard charger, and control modules. In a typical BYD car, the process starts with the physical connection: the PE (Protective Earth) terminal of the charging gun connects first, followed by the L (Live) and N (Neutral) terminals. Subsequently, the CC (Connection Confirm) and CP (Control Pilot) terminals engage. The CP signal plays a critical role in communication, with voltage transitions indicating connection status and charging readiness.
The CP signal in a BYD EV should follow a specific sequence: initially at 12 V DC when disconnected, it drops to 9 V DC upon partial connection, then switches to a 9 V PWM signal, and finally to a 6 V PWM signal when the vehicle is ready to charge. This can be represented mathematically for clarity. The voltage transitions are defined by the following equations, where $V_{CP}$ denotes the CP voltage:
$$V_{CP} = 12\, \text{V} \quad \text{(Disconnected State)}$$
$$V_{CP} = 9\, \text{V} \quad \text{(Partial Connection)}$$
$$V_{CP} = 9\, \text{V}_{PWM} \quad \text{(Initialization)}$$
$$V_{CP} = 6\, \text{V}_{PWM} \quad \text{(Charing Readiness)}$$
Additionally, the resistance at detection points verifies the connection. For instance, the combined resistance $R_{total} = R_C + R_4$ indicates a semi-connected state, while $R_{total} = R_C$ confirms full connection. Here, $R_C$ is the characteristic resistance, and $R_4$ is a fixed resistor in the circuit.
In this BYD EV case, I used a diagnostic tool to check for trouble codes, but none were stored. The data stream from the onboard charger revealed a PWM duty cycle of 0%, while the charging gun connection status was normal, and the vehicle state indicated “charging.” This discrepancy suggested an issue with the CP signal. To investigate further, I referred to the charging system circuit diagram and performed measurements with an oscilloscope on the CP terminal at the vehicle’s charging port.
The expected CP signal waveform for a properly functioning BYD car should show the voltage transitions described above. However, in this instance, the CP signal remained at a constant 12 V DC without transitioning to PWM, as shown in the table below summarizing the ideal vs. observed states:
| Stage | Expected CP Signal | Observed CP Signal |
|---|---|---|
| Disconnected | 12 V DC | 12 V DC |
| Partial Connection | 9 V DC | 12 V DC (No Change) |
| Initialization | 9 V PWM | No Transition |
| Charging Readiness | 6 V PWM | No Transition |
This indicated a fault in the CP signal path, likely due to an open circuit between the charging port and the power distribution unit in the BYD EV. Using a multimeter, I measured the resistance along the CP line. The circuit involves connectors such as KB53(B)/1 at the charging port and BK46/5 at the power distribution unit, with an intermediate connector KJB01/BJK01. The resistance measurements are summarized below:
| Measurement Point | Expected Resistance | Measured Resistance |
|---|---|---|
| KB53(B)/1 to BK46/5 | Low (e.g., < 1 Ω) | OL (Open Loop) |
| BK46/5 to BJK01/2 | Low (e.g., 0.2 Ω) | 0.2 Ω |
| KB53(B)/1 to KJB01/2 | Low (e.g., < 1 Ω) | OL (Open Loop) |
The open circuit between KB53(B)/1 and KJB01/2 confirmed a break in the wiring. This break prevented the CP signal from propagating correctly, causing the BYD car to fail in recognizing the charging state. The resistance can be modeled as $R = \infty$ for an open circuit, whereas a healthy connection should have $R \approx 0\, \Omega$.
To resolve the issue, I repaired the faulty wire between the KB53(B)/1 terminal and the KJB01/2 connector. After the repair, the CP signal transitions returned to normal, and the BYD EV successfully initiated charging. The instrument panel then displayed the expected charging information, confirming the fix.
In summary, diagnosing slow charging failures in a BYD EV requires a systematic approach. Key steps include understanding the charging principles, analyzing data streams, and performing electrical measurements. For this BYD car, the CP signal was critical, and its failure due to an open circuit highlighted the importance of verifying wiring integrity. Regular maintenance and thorough inspections can prevent such issues in BYD EV models, ensuring reliable performance. The overall process can be generalized using the formula for fault probability $P_{fault}$ based on signal integrity:
$$P_{fault} = 1 – e^{-\lambda t}$$
where $\lambda$ represents the failure rate of components, and $t$ is time. By monitoring signals like CP and CC, technicians can quickly isolate faults in BYD EV charging systems, enhancing efficiency and customer satisfaction.