In my extensive research on the BYD EV, specifically focusing on the BYD car’s electronic parking brake (EPB) system, I have delved into the intricate control logic and common failures that affect its operation. The EPB system is a critical safety feature in modern BYD EV models, ensuring stable parking and preventing unintended vehicle movement. However, malfunctions such as failure to engage or release can pose significant risks, including accidents or brake system damage. This article presents a first-person perspective analysis of the EPB system in the BYD EV, exploring its components, operational principles, and methodologies for diagnosing and resolving faults. Through experimental validation, I have verified the control logic and developed systematic approaches to address issues, emphasizing the importance of understanding the BYD car’s electrical architecture and employing modern diagnostic tools. To enhance clarity, I incorporate tables and mathematical formulations to summarize key concepts, and I include a visual reference to illustrate the system setup in the BYD EV.
The BYD EV’s electronic parking brake system comprises several core components: a 12V lead-acid battery, fuses, left and right EPB motors, an EPB switch, and an EPB control unit. In the BYD car, this system operates electronically, allowing drivers to activate or deactivate the brake via the switch, which sends signals to the control unit for motor execution. The power distribution involves multiple circuits; for instance, the battery supplies constant power through fuses like F2/47 and F2/48 to the EPB motors, while the ignition (IG1) relay provides switched power to the control unit. Ground connections and CAN bus links to the gateway controller facilitate communication and control. My analysis of the BYD EV’s circuit diagrams reveals that the EPB control unit manages motor operations based on switch inputs, with voltage levels indicating different states. For example, when the EPB switch is not engaged, specific terminals exhibit near-zero voltage, whereas engagement alters these values, reflecting the control logic. This setup in the BYD car ensures reliable performance, but faults can arise from various sources, which I categorize and analyze in subsequent sections.
To understand the EPB system’s behavior in the BYD EV, I derived mathematical representations of its operational principles. The voltage relationships at the EPB switch terminals can be modeled using basic circuit theory. Let $$V_{\text{battery}}$$ represent the battery voltage, typically around 12.00 V. When the switch is idle, the voltages at terminals K31/9 and K31/19 approximate 0 V, while K31/10 and K31/18 are close to $$V_{\text{battery}}$$. Upon pulling the switch, the voltages at K31/9, K31/10, and K31/18 equalize to approximately 8.00 V, which is less than $$V_{\text{battery}}$$ due to internal resistance and voltage division. This can be expressed as: $$V_{\text{switch}} = V_{\text{battery}} – I \cdot R_{\text{internal}}$$ where $$I$$ is the current and $$R_{\text{internal}}$$ is the resistance in the circuit. Similarly, pressing the switch sets K31/9, K31/18, and K31/19 to near 0 V, with K31/10 at $$V_{\text{battery}}$$. For the motors, the resistance between terminals, such as K31/14 and K31/29 for the left motor, is measured to be around 4.5 Ω, indicating normal operation if within specified limits. The power supply to the control unit follows Ohm’s law: $$V = I \cdot R$$, where deviations can signal faults. In the BYD EV, these equations help quantify system health and guide diagnostic procedures.
Common faults in the BYD car’s EPB system often stem from electrical, mechanical, or software issues. Based on my experiments with the BYD EV, I have identified five primary fault categories, which I summarize in the table below. This classification aids in systematic troubleshooting, especially when using diagnostic tools like code readers or multimeters.
| Fault Type | Possible Causes | Diagnosis Methods | Typical Symptoms in BYD Car |
|---|---|---|---|
| Power Supply Issues | Blown fuses (e.g., F2/47, F2/48), low battery voltage, poor connections | Measure voltage at terminals (e.g., K31/15, K31/13), inspect fuses visually or with resistance tests | No motor sound when operating EPB switch, vehicle unable to hold position on slopes |
| Wiring Faults | Open circuits, short circuits (to power or ground), loose connections due to vibration or corrosion | Check voltage drops and resistance along wires; e.g., if voltage approaches $$V_{\text{battery}}$$, short to power suspected | Inconsistent EPB operation, error codes indicating communication failures |
| Switch Malfunctions | Internal failure of EPB switch, damaged contacts | Verify switch backlight illumination, test signal voltages at terminals (K31/9, K31/10, etc.) during operation | No response to switch inputs, despite power being present |
| Motor Failures | Worn-out motors, internal faults in left or right EPB motors | Measure motor resistance (e.g., between K31/14 and K31/29); normal range is 4.0–5.0 Ω for BYD EV | One or both motors unresponsive, even with correct voltage supply |
| Control Unit or Software Errors | EPB control unit hardware failure, corrupted software or programming issues | Use diagnostic tools to read fault codes, reprogram or replace control unit if other causes ruled out | Systematic failures not resolved by component checks, persistent error messages |
In the BYD EV, these faults can manifest as unilateral or bilateral motor inactivity. For instance, a power supply issue might affect one motor if a specific fuse blows, whereas a control unit error could disable both. My approach involves starting with simple checks, such as visual inspections and voltage measurements, before progressing to complex diagnostics. The resistance of the EPB motors can be calculated using the formula: $$R_{\text{motor}} = \frac{V_{\text{applied}}}{I_{\text{measured}}}$$ where $$V_{\text{applied}}$$ is the voltage across the motor terminals and $$I_{\text{measured}}$$ is the current. In the BYD car, normal motor resistance values are critical for efficient operation; deviations indicate potential faults. Additionally, the voltage at the EPB switch terminals during engagement can be analyzed using Kirchhoff’s laws to identify abnormalities. For example, if the voltage at K31/9 does not change during switch activation, it suggests an open circuit, which I have encountered in practical scenarios with the BYD EV.
To validate these findings, I conducted an experiment on a 2020 BYD EV model exhibiting EPB system failure. The vehicle started normally and displayed an “OK” status but showed a “Check Electronic Parking Brake System” warning on the dashboard. When attempting to engage the EPB, no motor sound was audible, and the vehicle rolled on slopes, indicating a complete system failure. Using a diagnostic scanner, I retrieved fault codes pointing to left and right motor state mode errors and an EPB switch fault. This aligned with my initial hypothesis for the BYD car, prompting a detailed electrical analysis. I measured voltages at key terminals: K31/15 and K31/13 showed approximately 13.36 V, confirming adequate power supply. However, terminals for the motors (K31/14, K31/29, K31/12, K31/27) displayed voltages around 6.00 V regardless of switch operation, indicating an inconsistency. Further tests on the EPB switch terminals revealed that K31/9 remained at 0.07 V during both pull and press actions, unlike the expected behavior where it should shift to 8.00 V when pulled. Resistance measurements between K31/9 and other terminals during switch activation showed open circuit conditions (indicated as OL on the multimeter), specifically between KJG02/22 and K31/9. This confirmed a wiring fault—an open circuit in the harness connecting the EPB switch to the control unit. After repairing this section, I cleared the fault codes, and the BYD EV’s EPB system resumed normal function, demonstrating the efficacy of this diagnostic approach.
This case study underscores the importance of a methodical process in troubleshooting the BYD EV’s EPB system. By applying the control logic derived from circuit diagrams, I could isolate the fault efficiently. The relationship between voltage and resistance in the BYD car’s system can be generalized using the formula for voltage drop: $$\Delta V = I \cdot R_{\text{wire}}$$ where $$\Delta V$$ is the voltage loss across a wire, $$I$$ is the current, and $$R_{\text{wire}}$$ is the wire resistance. In instances of high resistance or open circuits, $$\Delta V$$ becomes significant, leading to operational failures. Moreover, the EPB control logic in the BYD EV involves Boolean conditions for switch states; for example, the engagement condition can be represented as: $$\text{Engage} = (S_{\text{pull}} = \text{high}) \land (V_{\text{K31/9}} \approx 8.00\, \text{V})$$ where $$S_{\text{pull}}$$ is the pull signal and $$\land$$ denotes logical AND. Violations of these conditions, as seen in the fault case, necessitate wiring repairs. The table below summarizes the diagnostic parameters and their implications for the BYD EV, based on my experimental data.
| Parameter | Normal Value | Fault Indicator | Mathematical Expression |
|---|---|---|---|
| Voltage at K31/15 (Power Supply) | ≈13.36 V | Low voltage suggests fuse or connection issue | $$V \geq 12.5\, \text{V}$$ for proper operation |
| Resistance of Left EPB Motor | 4.47 Ω | High resistance indicates motor damage | $$R_{\text{motor}} = 4.5 \pm 0.5\, \Omega$$ |
| Voltage at K31/9 (Switch Signal) | 0 V (idle), 8 V (pulled) | Constant voltage suggests open circuit | $$V_{\text{K31/9}} = f(S_{\text{switch}})$$ |
| Current Through EPB Motor | 2–3 A (estimated) | Zero current implies open circuit or motor failure | $$I = \frac{V}{R}$$ |
In conclusion, my investigation into the BYD EV’s electronic parking brake system highlights the critical role of control logic in fault diagnosis and resolution. Through hands-on experimentation, I have demonstrated that a deep understanding of the BYD car’s electrical systems, combined with mathematical modeling and systematic testing, can effectively address common issues like wiring faults or component failures. The integration of tables and formulas, as presented, provides a structured framework for technicians and researchers working on the BYD EV. This exploratory learning not only validates the EPB control logic but also enhances the reliability and safety of the BYD EV, reinforcing the importance of continuous innovation in automotive electronics. As electric vehicles like the BYD car evolve, such diagnostic methodologies will remain essential for maintaining high performance standards.