As an automotive technician specializing in electric vehicles, I recently encountered a challenging case involving a BYD EV model, specifically a 2021 BYD Qin EV. The vehicle had accumulated approximately 53,000 km and was brought in with a complaint that the OK light illuminated normally, but upon pressing the acceleration pedal, the instrument panel cycled through warnings such as “Check Power System,” “Check ESP System,” and “Check Electronic Parking System.” Additionally, the electronic parking system failed to release automatically, and even manual release did not allow the BYD car to move. This issue directly impacted the drivability of the BYD EV, highlighting the critical role of sensor integration in modern electric vehicles.
Upon initial inspection, I confirmed the fault as described. The OK light indicated that the vehicle’s basic systems were operational, but the recurring warnings and inability to move suggested a deeper issue within the powertrain or related control systems. In BYD EV models, the acceleration pedal position sensor is a key component that feeds data to the Vehicle Control Unit (VCU), which then coordinates with systems like the ESP and electronic parking brake. Any discrepancy in this signal can trigger multiple faults, as observed here.
To begin the diagnosis, I connected a professional diagnostic tool to the BYD car’s onboard system. The tool retrieved several fault codes: P1D7B00 (Acceleration Pedal Signal Fault – Signal 1 Malfunction), P1D7C00 (Acceleration Pedal Signal Fault – Signal 2 Malfunction), and P1D6600 (Acceleration Pedal Fault – Verification Error). These codes pointed directly to issues with the acceleration pedal position sensor, which in BYD EV vehicles typically consists of two redundant signals for safety and accuracy. The presence of a verification error indicated that the VCU detected an inconsistency between the two signals, leading to a system-wide fault condition.
Next, I proceeded to analyze the data stream from the diagnostic tool to gather real-time information. While gradually depressing the acceleration pedal, I monitored key parameters. The data showed that the “Acceleration Pedal Depth” varied from 0% to 97%, and “Acceleration Pedal Depth Voltage 1” changed from 0.74 V to 4.8 V, which aligned with expected ranges. However, “Acceleration Pedal Depth Voltage 2” remained constant at 0 V, showing no variation. This anomaly suggested that Signal 2 from the acceleration pedal position sensor was not functioning, likely causing the verification fault and subsequent system warnings in the BYD EV.
To better understand the underlying cause, I referred to the technical documentation for BYD EV models, which outlines the circuit design for the acceleration pedal position sensor. In general, BYD cars use a dual-redundant sensor system where two separate signals (Signal 1 and Signal 2) are sent to the VCU to ensure reliability. Signal 1 typically operates in a higher voltage range, while Signal 2 provides a complementary lower voltage range; the VCU cross-checks these signals for consistency. Based on the fault codes and data stream, I hypothesized several potential causes for the failure in this BYD EV: a faulty acceleration pedal position sensor unit itself, a localized issue with the VCU, or wiring problems in the sensor circuit, such as open circuits, short circuits, or poor connections.
To systematically evaluate these possibilities, I focused on the electrical measurements. With the ignition switch turned on, I used a digital multimeter to measure voltages at the VCU connector terminals related to the acceleration pedal position sensor. For convenience, I targeted terminals GK49/24 (associated with Signal 1 power or reference), GK49/48 (associated with Signal 2 output), and GK49/38 (ground reference). The measurements were conducted while smoothly operating the acceleration pedal to simulate normal driving conditions in the BYD car. The results are summarized in the table below, which compares the standard expected values against the actual readings.
| Measurement Condition | Terminal GK49/24 to Ground Voltage | Terminal GK49/48 to Ground Voltage | Terminal GK49/38 to Ground Voltage | Standard Description | Conclusion |
|---|---|---|---|---|---|
| Ignition ON, gradual acceleration pedal press | 13.4 V | 0 V (no change) | 0 V | +B (approx. 12-14 V); 0.35 V to 2.25 V for signal variation | Normal for GK49/24 and GK49/38; Abnormal for GK49/48 |
The voltage at terminal GK49/24 was 13.4 V, which is within the expected range for the supply voltage in a BYD EV battery system. Terminal GK49/38 showed 0 V, correctly indicating ground. However, terminal GK49/48 remained at 0 V without any change, whereas it should have varied between approximately 0.35 V and 2.25 V based on the pedal position. This confirmed an issue with Signal 2. To isolate the problem, I then measured the voltages directly at the acceleration pedal position sensor connector terminals—specifically, terminal 2 (power supply), terminal 1 (Signal 2 output), and terminal 6 (ground). The results are presented in the following table.
| Measurement Condition | Terminal 2 to Ground Voltage | Terminal 1 to Ground Voltage | Terminal 6 to Ground Voltage | Standard Description | Conclusion |
|---|---|---|---|---|---|
| Ignition ON, gradual acceleration pedal press | 13.4 V | 0.34 V to 2.26 V | 0 V | +B (approx. 12-14 V); 0.35 V to 2.25 V for signal variation; 0 V for ground | Normal for all terminals at sensor side |
At the sensor side, terminal 2 showed 13.4 V (normal supply), terminal 1 displayed a varying voltage from 0.34 V to 2.26 V (which aligns with the expected Signal 2 range), and terminal 6 was at 0 V (proper ground). This indicated that the acceleration pedal position sensor itself was functioning correctly in this BYD EV, as it generated the appropriate Signal 2 output. The discrepancy between the sensor output and the VCU input suggested a fault in the wiring harness connecting the two. Specifically, the circuit between terminal 1 of the sensor and terminal GK49/48 of the VCU appeared to have an open circuit, preventing Signal 2 from reaching the VCU.
To confirm this hypothesis, I turned off the ignition and disconnected the battery negative terminal for safety. I then detached the connectors at both the VCU and the acceleration pedal position sensor. Using the multimeter in resistance mode, I measured the resistance between VCU terminal GK49/48 and sensor terminal 1. The reading was infinite resistance (∞ Ω), confirming an open circuit in the wire. This break in the circuit explained why Signal 2 was not being transmitted, leading to the verification fault and the overall system failure in the BYD car.
The relationship between the acceleration pedal position and the sensor outputs can be described using linear equations, which are fundamental in BYD EV designs for accurate control. For instance, the voltage output for Signal 1 (V1) and Signal 2 (V2) should ideally follow: $$ V1 = k1 \cdot \theta + c1 $$ and $$ V2 = k2 \cdot \theta + c2 $$ where $\theta$ represents the pedal angle or depth (from 0% to 100%), $k1$ and $k2$ are scaling factors, and $c1$ and $c2$ are offset voltages. In a properly working BYD EV, these signals should correlate closely, with the VCU performing a verification check such as $$ |V1 – f(V2)| < \epsilon $$ where $f$ is a transformation function and $\epsilon$ is a tolerance threshold. If this condition is violated, as in this case where V2 was stuck at 0 V at the VCU, the VCU triggers fault codes and disables critical systems to ensure safety.
With the fault identified, I proceeded to repair the wiring. Following standard procedures for BYD EV repairs, I carefully traced the harness between the VCU and the acceleration pedal position sensor, located the break in the wire, and soldered and insulated the connection securely. After reassembling the components and reconnecting the battery, I performed a comprehensive test. Starting the BYD car, I observed that the OK light illuminated, and the instrument panel no longer displayed the warning messages. Upon pressing the acceleration pedal, the electronic parking system released automatically, and the vehicle moved smoothly without any issues. Data stream verification showed that both “Acceleration Pedal Depth Voltage 1” and “Acceleration Pedal Depth Voltage 2” now varied correctly with pedal input, confirming the resolution of the fault.
This case underscores the importance of the acceleration pedal position sensor in BYD EV models. Not only does it control vehicle speed, but it also interfaces with systems like the ESP and electronic parking brake for enhanced driver convenience and safety. In BYD cars, a failure in this sensor or its circuitry can have cascading effects, leading to multiple system warnings and immobilization. The diagnosis process highlighted the value of methodical electrical measurements and data analysis, which are crucial for efficient troubleshooting in modern electric vehicles. For future reference, technicians working on BYD EV models should prioritize checking wiring integrity, especially in high-vibration areas, to prevent similar issues. Regular maintenance and system scans can also help detect early signs of sensor or circuit degradation in BYD cars, ensuring reliable performance and customer satisfaction.
In summary, the inability of this BYD EV to drive was resolved by addressing an open circuit in the acceleration pedal position sensor wiring. The integration of diagnostic tools, circuit analysis, and hands-on measurements proved effective in pinpointing the fault. This experience reinforces that even minor wiring issues can cause significant disruptions in advanced BYD EV systems, emphasizing the need for thorough and precise repair techniques in the evolving automotive landscape.