As an experienced automotive technician specializing in BYD car models, I recently encountered a challenging case involving a 2019 BYD Tang DM, a plug-in hybrid electric vehicle (PHEV) that exemplifies the complexities of modern BYD EV systems. The owner reported an inability to charge the vehicle using various charging stations, with the dashboard displaying a “Check On-board Charging System” warning. This issue not only highlights the critical nature of charging infrastructure for BYD EV owners but also underscores the importance of precise diagnostic procedures in high-voltage systems common to BYD car technologies.
The vehicle in question, a BYD Tang DM with all-wheel drive and a 2.0L engine, had accumulated approximately 59,612 km. Initial inspection revealed that the charging process would initiate briefly before automatically disconnecting, consistently triggering the same warning message. Using a professional diagnostic scanner, I retrieved a current fault code P157217, indicating “On-board Charger DC Side Voltage High.” This code persisted even after attempted resets, pointing to a potential hardware or configuration issue within the BYD EV charging system.
To understand the fault better, it is essential to grasp the charging control logic in BYD car models. The on-board charger (OBC) manages AC power input and communicates with the Battery Management System (BMS) to enable charging. Upon connection, the OBC supplies low-voltage power to the BMS and high-voltage distribution unit. After receiving charging permission, the BMS engages contactors, allowing the OBC to detect the battery pack’s back-emf and output charging voltage. The fault code P157217 is triggered under specific conditions related to DC side voltage anomalies, such as excessive voltage slope or absolute values exceeding thresholds. For instance, if the DC output voltage slope surpasses 80 V per 20 microseconds, or if the RMS voltage exceeds the charging上限 by 10 V for 100 ms, the system logs this fault. This mechanism is critical for protecting BYD EV components from overvoltage damage.
My diagnostic approach began with verifying software integrity, as outdated firmware can cause irregularities in BYD car systems. All control modules, including the OBC and BMS, were confirmed to be running the latest versions, eliminating software as a root cause. Next, I performed a physical inspection of the charging port and connections, which appeared secure and undamaged. Using the diagnostic tool, I monitored real-time data streams from the OBC, which showed a DC side voltage reading of 593 V, flagged as a severe fault. This abnormal voltage level, compared to the expected range, suggested an underlying hardware issue.
To systematically evaluate potential causes, I referred to the vehicle’s wiring diagrams and conducted electrical tests. The following table summarizes the key measurements taken during the initial inspection:
| Component | Parameter | Measured Value | Normal Range |
|---|---|---|---|
| OBC Low-Voltage Connector | Supply Voltage | 12.1 V | 11-14 V |
| OBC Low-Voltage Connector | Ground Resistance | 0.2 Ω | < 1 Ω |
| OBC DC Output | Insulation Resistance | 2.5 MΩ | > 1 MΩ |
| Battery Pack Voltage | High-Voltage Output | 586 V | ~600 V (nominal) |
All low-voltage circuits, including power, ground, and communication lines, tested within specifications, with no signs of pin damage or corrosion. The insulation resistance between DC positive and negative terminals was adequate, ruling out short circuits. Given these results, I suspected a fault in the OBC itself and performed a substitution test with a known-good unit from another BYD EV. However, the fault persisted, indicating that the OBC was not the primary issue. Cross-referencing the part number confirmed compatibility, so I shifted focus to other high-voltage components.
Further discussion with the owner revealed that the vehicle had previously been serviced at an independent repair shop for an “EV Function Restricted” error, during which the high-voltage distribution box was reportedly repaired, including replacement of power relays. This history raised suspicions about improper reassembly. I proceeded to dismantle the high-voltage distribution box for a thorough inspection. Inside, I checked fuses, relays, and the pre-charge resistor, all of which showed normal continuity and resistance values. The pre-charge resistor measured 199.5 Ω, close to the nominal 200 Ω, suggesting it was functional. However, upon comparing the wiring layout with technical diagrams, I discovered that the pre-charge resistor’s connections were reversed—a critical error introduced during the previous repair.
In BYD EV systems, the pre-charge circuit is vital for managing inrush currents when high-voltage contactors close. The circuit typically includes a pre-charge contactor and resistor, which limit current flow to charge capacitive loads, such as those in motor controllers, gradually. This prevents excessive current surges that could damage components. The pre-charge process can be modeled using the following equations, which describe the voltage across the capacitor during pre-charging:
$$ V_c(t) = V_{\text{battery}} \left(1 – e^{-\frac{t}{R_{\text{pre}} C}}\right) $$
where \( V_c(t) \) is the capacitor voltage at time \( t \), \( V_{\text{battery}} \) is the battery voltage, \( R_{\text{pre}} \) is the pre-charge resistance, and \( C \) is the equivalent capacitance. The pre-charge current \( I_{\text{pre}}(t) \) is given by:
$$ I_{\text{pre}}(t) = \frac{V_{\text{battery}} – V_c(t)}{R_{\text{pre}}} $$
In this BYD car, the reversed connections bypassed the pre-charge resistor, eliminating the current-limiting effect. Consequently, when the contactors engaged during charging, the full battery voltage was applied instantaneously to the OBC, causing a voltage spike that exceeded the OBC’s thresholds and triggered fault code P157217. This miswiring effectively disabled the pre-charge sequence, leading to the observed charging failure.
After correcting the pre-charge resistor connections, I performed multiple charging tests to validate the repair. The vehicle successfully charged without warnings, and diagnostic scans confirmed no recurring fault codes. The table below outlines the key parameters before and after the repair, emphasizing the impact of the pre-charge circuit on system behavior:
| Parameter | Before Repair | After Repair |
|---|---|---|
| DC Side Voltage (OBC Data Stream) | 593 V (Fault) | ~586 V (Normal) |
| Charging Duration | Few seconds before disconnect | Sustained until full charge |
| Fault Code Status | P157217 (Current) | No faults |
| Pre-charge Resistance | Effective bypass due to reversed wires | 199.5 Ω (Properly connected) |
This case highlights the intricacies of BYD EV high-voltage systems and the necessity for meticulous repair practices. The pre-charge mechanism is not just a safety feature but a fundamental aspect of preserving component longevity in BYD car architectures. For example, the energy dissipated during pre-charging can be approximated as:
$$ E_{\text{pre}} = \int_0^{t_{\text{pre}}} I_{\text{pre}}(t) V_c(t) dt $$
where \( t_{\text{pre}} \) is the pre-charge duration. Improper wiring, as in this instance, can lead to uncontrolled energy transfer, increasing the risk of insulation breakdown or contactor welding.
In conclusion, diagnosing and resolving charging issues in BYD EV models requires a holistic understanding of both electrical principles and vehicle-specific designs. This BYD car incident underscores how minor assembly errors can precipitate significant faults, reinforcing the need for standardized procedures in high-voltage repairs. As BYD EV technologies evolve, technicians must prioritize continuous education and adherence to manufacturer guidelines to ensure reliability and safety. Regular verification tests post-repair, such as charging cycles and data stream analyses, are indispensable for preventing recurrences. Ultimately, this experience with the BYD Tang DM reaffirms the importance of precision in maintaining the integrity of advanced BYD car systems, safeguarding both vehicle performance and user trust in electric mobility.