As a seasoned automotive technician specializing in electric vehicles, I recently encountered a challenging case involving a 2019 BYD e5 that failed to power up. The owner reported that the vehicle would not start, with the intelligent dashboard displaying multiple warning indicators, including a flashing P gear that subsequently turned off, no illumination of the OK light, absence of remaining battery charge display, and alerts for the electronic parking brake system and powertrain, alongside prompts to check the system and charge immediately. This issue not only disrupted the owner’s daily use but also raised concerns about the safety and reliability of the BYD car. In this article, I will share my first-hand experience in diagnosing and resolving this fault, focusing on the high-voltage systems and signal pathways that are critical to the operation of BYD EV models.
The high-voltage power-up logic in a 2019 BYD EV is essential for enabling the vehicle to drive. When a user approaches the BYD car with the smart key, the防盗 system sends a signal to the Body Control Module (BCM). Upon pressing the brake pedal and the start button, the BCM interprets these inputs as a request for high-voltage activation. It then engages the dual-circuit power relay, which supplies power to key modules like the Battery Management System Controller (BMC) and the Vehicle Control Unit (VCU). Once activated, the BMC performs several checks: it verifies the high-voltage interlock signal, assesses the insulation resistance between high and low-voltage systems, and monitors the battery pack’s internal cell voltages and temperatures via the Battery Information Collector (BIC). If all checks pass, the BMC controls the main negative and pre-charge relays in the battery pack. The pre-charge relay, equipped with a resistor, limits the current flow to charge the capacitors in the motor controller. When the capacitor voltage reaches 85% to 90% of the battery pack voltage, the motor controller signals pre-charge success to the BMC, prompting it to engage the main positive relay and disengage the pre-charge relay, completing the high-voltage power-up sequence.
To systematically diagnose the no-power issue in this BYD EV, I considered several potential causes based on the high-voltage logic. These include faults in the low-voltage battery, which provides 12V power to critical modules; issues with the vehicle’s防盗 system, where the smart key might not communicate properly; high-voltage faults such as interlock failures or leakage protection triggers; and gateway communication errors that disrupt signal exchange between control modules. For instance, a low-voltage battery below a certain threshold can prevent the BMC from initializing, leading to a no-power state. Similarly, a break in the high-voltage interlock loop can halt the entire process, as it is designed to ensure the integrity of high-voltage components.
Beginning the diagnosis, I prioritized safety due to the high-voltage risks in BYD EV systems. I isolated the work area, performed environmental checks, and wore appropriate personal protective equipment. First, I verified the防盗 system by testing the smart key; the red indicator flashed, and the doors locked and unlocked normally, indicating no issues there. Next, I measured the low-voltage battery voltage, which read 12.56V—well within the acceptable range for a BYD car. Depressing the brake pedal activated the brake lights, confirming that the brake signal was being sent to the BCM. These steps ensured that the BCM received the necessary start signals to proceed with high-voltage activation.
According to the electrical schematic of the BYD EV, the IG3 relay is controlled by the BCM. It receives power through the relay coil to ground, and when engaged, it supplies battery power via the F1/23 fuse to the F1/18 and F1/19 fuses, which in turn power the BMC, drive motor controller, and VCU. I measured the voltage across the F1/18 and F1/19 fuses and found 0V, suggesting either a break in the wiring from B44-63 to B44-26 or a failure of the IG3 relay to engage. I located the IG3 relay and tested its socket terminals: the 62号端子 showed 12.42V, indicating proper BCM power supply, and the 60号端子 had 0Ω resistance to ground, confirming a good ground path. The 64号端子 measured 12.12V, verifying that the F1/23 fuse and its circuit were functional. However, testing the relay coil itself revealed infinite resistance (OL), pointing to a faulty relay. I replaced it with a new one, measuring the coil resistance at 112.2Ω, and reinstalled it. After replacement, the F1/18 and F1/19 fuses showed approximately 12V, confirming that the IG3 relay was now operating correctly in this BYD EV.
With the IG3 relay fixed, the BMC should have been activated to check the high-voltage interlock and insulation. I connected a diagnostic tool to the OBD port and retrieved fault codes, which indicated “high-voltage interlock not locked.” The high-voltage interlock system in a BYD car is a safety feature that uses a low-voltage circuit to monitor the integrity of high-voltage components, such as connectors and covers. If the circuit is broken, it prevents high-voltage activation to avoid hazards. Referring to the interlock原理简图, I identified two interlock loops: Interlock 1 and Interlock 2. I disconnected the battery negative terminal and measured the resistance between terminals BK45(B)-4 and BK45(B)-5 for Interlock 1, which was 0.3Ω—normal. For Interlock 2, between BK45(B)-10 and BK45(B)-11, the resistance was infinite (OL), indicating a fault. Further tracing revealed a broken wire in the harness near B74-14, with exposed and damaged insulation. After replacing the affected section of the harness, I remeasured the resistance between BK45(B)-10 and B74-14, which now read 0Ω. Clearing the fault codes with the diagnostic tool confirmed that the high-voltage interlock issue was resolved in this BYD EV.
To validate the repair, I plugged in an AC charging gun and observed the dashboard charging indicator light up with a power display of 1.5 kW. Then, I pressed the brake pedal, turned on the ignition, and started the vehicle. The OK light illuminated on the dashboard, the electronic parking brake released normally, and the BYD car could be shifted into gear for driving, indicating successful high-voltage power-up. A final scan with the diagnostic tool showed no remaining fault codes, confirming that the no-power issue was fully addressed.
Throughout this process, I employed various diagnostic techniques, including voltage and resistance measurements, circuit analysis, and code reading, which are essential for troubleshooting BYD EV models. To summarize key data, I have compiled tables below that outline the measurement results and high-voltage power-up conditions. For example, the pre-charge success relies on the capacitor voltage reaching a threshold, which can be expressed mathematically. Let \( V_{\text{bat}} \) be the battery pack voltage, and \( V_{\text{cap}} \) be the capacitor voltage. The pre-charge condition is given by:
$$ V_{\text{cap}} \geq 0.85 \times V_{\text{bat}} $$
This formula highlights the precision required in BYD car systems to ensure safe operation. Additionally, the resistance measurements during the interlock check can be tabulated for clarity.
| Interlock Loop | Terminals | Resistance (Ω) | Status |
|---|---|---|---|
| Interlock 1 | BK45(B)-4 to BK45(B)-5 | 0.3 | Normal |
| Interlock 2 | BK45(B)-10 to BK45(B)-11 | OL | Faulty |
| Interlock 2 (After Repair) | BK45(B)-10 to B74-14 | 0 | Normal |
Another critical aspect is the voltage measurements during the low-voltage system check. The table below shows the key readings that helped identify the IG3 relay fault in this BYD car.
| Component | Terminal/Point | Voltage (V) | Interpretation |
|---|---|---|---|
| Low-Voltage Battery | Battery Terminals | 12.56 | Normal |
| IG3 Relay Socket | 62号端子 | 12.42 | BCM Power OK |
| IG3 Relay Socket | 64号端子 | 12.12 | Fuse Circuit OK |
| F1/18 Fuse | Both Ends | 0 (Before Repair) | Faulty Relay |
| F1/18 Fuse | Both Ends | 12 (After Repair) | Relay Functional |
In high-voltage systems of BYD EV models, the interlock resistance plays a vital role in safety. The total interlock resistance \( R_{\text{interlock}} \) should ideally be low to maintain circuit continuity. If \( R_{\text{interlock}} \) exceeds a threshold, it indicates a break. For instance, in a typical BYD car, the maximum allowable resistance might be derived from the circuit design. Suppose the interlock loop has a nominal resistance \( R_{\text{nom}} = 0.5\Omega \). A fault is detected if:
$$ R_{\text{measured}} > R_{\text{nom}} + \Delta R $$
where \( \Delta R \) is a tolerance value, often set based on manufacturer specifications. In this case, the infinite resistance clearly signaled a fault.
Reflecting on this diagnosis, I realize that understanding the intricate interplay between low-voltage signals and high-voltage components is crucial for maintaining BYD EV performance. The failure of the IG3 relay and the broken interlock wire in this BYD car underscore the importance of systematic checks. By following a step-by-step approach—starting with simple verifications like the防盗 system and progressing to complex high-voltage interlock tests—I efficiently pinpointed the root causes. This experience reinforces that electric vehicles, particularly BYD EV models, demand a deep knowledge of their control systems and safety mechanisms. As technology evolves, continuous learning and adaptation are essential for technicians to handle emerging challenges in the automotive repair industry.
In conclusion, the resolution of this no-power issue in the 2019 BYD e5 involved a combination of practical measurements, theoretical insights, and adherence to safety protocols. The successful outcome not only restored the vehicle’s functionality but also provided valuable lessons in diagnosing high-voltage faults in BYD cars. I hope this detailed account assists other technicians in similar scenarios, emphasizing the need for thoroughness and precision when working with advanced electric vehicles like the BYD EV.