As an automotive technician specializing in electric vehicles, I recently encountered a challenging case involving a BYD EV that refused to power on. The vehicle in question was a 2017 BYD E5 pure electric model, and the owner reported that upon pressing the start button while braking, the dashboard displayed a “Check Powertrain” warning without the green “OK” light illuminating. This prevented the BYD car from operating normally, indicating a failure in the high-voltage system. In this detailed account, I will walk through the entire diagnostic and repair process, emphasizing the critical role of safety protocols, systematic testing, and the importance of understanding high-voltage interlock systems in BYD EV models.
Before diving into the diagnostics, I prioritized safety measures to prevent any electrical hazards. High-voltage systems in BYD EV vehicles can be dangerous if mishandled, so I began by parking the car securely and placing wheel chocks to immobilize it. I then installed protective covers, including seat covers, floor mats, steering wheel covers, and gearshift covers, to maintain cleanliness and prevent damage. Additionally, I laid out insulating mats in the work area and wore personal protective equipment such as insulated shoes and a helmet. A safety warning sign was positioned nearby to alert others to the ongoing high-voltage work. These steps are standard for any BYD car repair to ensure both technician and vehicle safety.
With safety in place, I proceeded to verify the fault as described by the owner. I pressed the brake pedal and activated the start button, observing that the “OK” light did not illuminate, and the dashboard consistently showed the “Check Powertrain” message. This confirmed that the BYD EV was not achieving a proper power-on state, meaning the high-voltage battery was not supplying power to the drive system. Such symptoms often point to issues like high-voltage interlock faults, which are common in BYD EV models due to their complex electrical architecture.
To diagnose the problem, I started with the low-voltage system, as it powers the control circuits. I measured the voltage of the low-voltage iron battery using a digital multimeter. The results are summarized in the table below, which confirmed that the battery was within the normal operating range, and all connected wiring harnesses were secure without any looseness.
| Measurement Terminal | Standard Value (V) | Measured Value (V) | Result Analysis |
|---|---|---|---|
| +, – | 11–14 | 13.4 | Normal |
Since the low-voltage system was functional, I connected a diagnostic scanner to retrieve trouble codes. The scanner communicated successfully with the vehicle’s systems and reported a single fault code: P1A6000, indicating a high-voltage interlock failure. This code is critical in BYD EV models, as it relates to the safety loop that ensures all high-voltage components are properly connected before enabling high-voltage power. The high-voltage interlock system in a BYD car acts as a safeguard; if any high-voltage connector is loose or damaged, the interlock circuit opens, prompting the battery management system (BMS) to disconnect high-voltage contactors and prevent potential hazards like electric shocks or arcs.
To further investigate, I analyzed data streams from the vehicle’s control modules. The data revealed that while high-voltage interlock 1 was locked, interlocks 2 and 3 were not, pinpointing the fault to the interlock 1 circuit. This insight directed my focus toward the specific components involved in that circuit. In BYD EV designs, the high-voltage interlock loop typically includes the BMS, power battery pack, high-voltage electronic control unit (often integrated as a four-in-one unit), and modules like the air conditioning compressor and PTC heater. The interlock circuit forms a series connection through low-voltage wires and connectors, with each high-voltage plug containing a normally closed interlock switch. If any connector is disengaged, the circuit breaks, and the BMS detects this, leading to a shutdown. The overall resistance of a healthy interlock circuit can be expressed as: $$R_{\text{interlock}} = \sum_{i=1}^{n} R_i$$ where each \( R_i \) represents the resistance of a segment, and the total should be less than 1 Ω for proper operation.
Next, I examined the low-voltage control circuits associated with the high-voltage interlock. Using a digital multimeter set to the 200 Ω range, I measured resistances across various wiring harnesses between components. The following tables summarize the measurements, which all fell within acceptable limits, indicating no issues with the low-voltage wiring or connections.
| Measurement Terminals | Standard Value (Ω) | Measured Value (Ω) | Result Analysis |
|---|---|---|---|
| B52/2, B28(B)/22 | < 1 | 0.3 | Normal |
| Measurement Terminals | Standard Value (Ω) | Measured Value (Ω) | Result Analysis |
|---|---|---|---|
| B52/1, BK45(A)/22 | < 1 | 0 | Normal |
| Measurement Terminals | Standard Value (Ω) | Measured Value (Ω) | Result Analysis |
|---|---|---|---|
| BK45(B)/7, KxK51/30 | < 1 | 0.5 | Normal |
| Measurement Terminals | Standard Value (Ω) | Measured Value (Ω) | Result Analysis |
|---|---|---|---|
| BK45(B)/7, B28(B)/23 | < 1 | 0 | Normal |
After confirming the low-voltage circuits were intact, I moved on to inspect the high-voltage components and their interlock terminals. Wearing high-voltage insulated gloves, I checked connections at the BMS, power battery pack, high-voltage control unit, PTC module, and air conditioning compressor. For instance, I measured the resistance between terminals 29 and 30 on the power battery pack’s KxK51 connector, which showed 0 Ω, indicating a good connection. Similarly, terminals on other components were tested, but when I reached the high-voltage control unit’s B28(B) connector, terminals 22 and 23 displayed an infinite resistance, suggesting a fault. To isolate the issue, I systematically disconnected high-voltage connectors one by one and shorted the interlock tabs while measuring resistance. This method revealed that the air conditioning compressor connector had a damaged interlock tab, as shorting it resulted in 0 Ω resistance instead of the expected open circuit. This damage—likely due to previous repairs—prevented the interlock circuit from closing properly, causing the BYD EV to remain in a safe mode and not power on.
Although the vehicle did not show any insulation-related fault codes, I performed insulation tests to rule out potential leaks. Using a dedicated megohmmeter, I verified its functionality by performing open and short circuit checks. For example, with the meter set to 500 V, open-circuit measurements showed infinite resistance, and short-circuit measurements showed 0 Ω, confirming the tool was operational. I then tested the insulation between the air conditioning compressor’s high-voltage terminals and the vehicle chassis, as well as the high-voltage control unit’s terminals and its casing. The results, summarized below, exceeded the minimum requirement of 2 MΩ, indicating no insulation faults.
| Measurement Point | Standard Resistance (Ω) | Measured Value (Ω) | Result Analysis |
|---|---|---|---|
| Compressor terminals to chassis | > 2M | > 20M | Normal |
| Control unit terminals to casing | > 2M | > 20M | Normal |
With the fault pinpointed to the air conditioning compressor’s high-voltage harness, I consulted the vehicle’s VIN to order a genuine replacement part. After installing the new harness and reconnecting all low-voltage and high-voltage connections, I reinstalled the manual service plug and reconnected the low-voltage battery negative terminal. Upon activating the start switch, the green “OK” light illuminated immediately, and the BYD EV powered on successfully, confirming that the repair resolved the issue. The entire process underscored the importance of methodical testing and adherence to safety protocols when working on high-voltage systems in BYD car models.
In conclusion, diagnosing and repairing high-voltage interlock failures in BYD EV vehicles requires a thorough understanding of the interlock circuit原理 and a step-by-step approach. Key takeaways include the necessity of safety precautions, the use of diagnostic tools to read fault codes and data streams, and systematic resistance and insulation measurements. For this BYD car, the root cause was a damaged interlock tab in the air conditioning compressor connector, which disrupted the high-voltage interlock loop. By replacing the faulty high-voltage harness, the vehicle was restored to full functionality. This case highlights how even minor component damage can lead to significant issues in electric vehicles, and it reinforces the value of comprehensive troubleshooting in maintaining the reliability and safety of BYD EV models. Future repairs on similar BYD EV systems should always begin with verifying the interlock circuit integrity, as it is a common failure point that can prevent the vehicle from powering on.