High-Voltage Failures in Electric Vehicles (EVs): Troubleshooting and Solutions

High-Voltage Failure in EVs: Troubleshooting and Countermeasures

Due to the numerous electrical components in EVs, high-voltage failures often occur during use for various reasons, causing the vehicle to fail to operate normally. This brings significant inconvenience to users. During repairs, the occasional nature of some faults makes the troubleshooting process difficult and it is often challenging to determine the direction of investigation. Based on practical experience, this article summarizes several common situations of high-voltage failure in electric vehicles, along with troubleshooting methods and countermeasures, hoping to provide some reference and assistance to relevant technicians.

High-Voltage Failure in Electric Vehicles (EVs): Troubleshooting and Solutions

High-voltage failures are common in electric vehicles (EVs) due to the numerous electrical components involved. These failures can prevent the vehicle from operating normally, leading to significant inconvenience for users. Since some faults are intermittent, troubleshooting can be challenging, and it may be hard to identify where to begin the investigation. Based on practical experience, this article summarizes several typical scenarios of high-voltage failures in electric vehicles and provides troubleshooting methods and solutions, offering guidance for technicians in the field.

I. Abnormal Power Supply to Key Controllers in the Electric Powertrain

Power Loss to Key Controllers (VCU, BMS, MCU) Leading to High-Voltage Loss

Troubleshooting:
If the high-voltage fails to restore after a drop, measure the voltage at the low-voltage power supply terminals of the Vehicle Control Unit (VCU), Battery Management System (BMS), and Motor Control Unit (MCU). If there is no power at these terminals, check if the positive and negative terminals of the battery are securely connected and ensure there are no loose connections. Verify that the power supply lines to these controllers are intact.

Solution:
If the battery’s positive and negative terminals are loose, reconnect them. If any power supply lines are broken or disconnected, use a multimeter to trace and repair the damaged wiring.

Troubleshooting:
If high-voltage is restored after turning the key to the “Start” position, but the voltage drops again after a period, this might be an intermittent fault caused by loose low-voltage connectors at the VCU, BMS, or MCU, or possibly loose battery connections. This can result in power loss due to poor contact.

Solution:
If any low-voltage connectors are improperly connected, reseat or replace them. If any power supply lines are loose, tighten them. If the battery’s terminals are loose, secure them.

Abnormal Power Supply Voltage to Key Controllers (VCU, BMS, MCU), Too Low or Too High

Troubleshooting:
Check the status of the DC-DC converter. If it is not working and its output is 0V, it indicates the battery is discharging continuously, causing the voltage to drop too low, which can trigger a low-voltage condition for the VCU, BMS, and MCU.

Solution:
In this case, further investigation is needed to determine why the DC-DC converter failed. Repair or replace the converter as necessary.

Troubleshooting:
If the DC-DC converter is working but the output voltage is too high—exceeding the normal operating range of the controllers—this could trigger a high-voltage loss request.

Solution:
Investigate the root cause of the high output voltage and repair the DC-DC converter accordingly.

II. Vehicle CAN Communication Failure

Controller Failure Sending Error Frames, Causing CAN Communication Failure and High-Voltage Loss

Troubleshooting:
If high-voltage cannot be restored after a drop, disconnect each controller in the vehicle’s CAN (Controller Area Network) system one by one and check if the high-voltage is restored. If disconnecting a specific controller restores high-voltage, this indicates that the fault lies with that controller.

Solution:
Analyze the faulty controller, and if necessary, replace the component.

Troubleshooting:
Check the supply voltage to the VCU, BMS, and MCU controllers. Use a CAN logger to capture data and analyze communication when high-voltage loss occurs. Identify which controller’s message is abnormal, confirming the faulty controller.

Solution:
Analyze the faulty controller and replace it if needed.

Loose or Faulty Controller Connectors Causing Message Loss, Triggering Communication Failure and High-Voltage Loss

Troubleshooting:
Review the fault messages and check for missing data during the high-voltage drop. Check whether the low-voltage connectors to the controllers are properly inserted, undamaged, and that CAN pins are secure without any loose connections.

Solution:
If the connector is loose or damaged, reseat or replace it. Tighten the CAN pins or replace any faulty connectors.

Water Ingress into Controller Connectors Causing CAN Communication Failure

Troubleshooting:
If the CAN network shows error frames across all controllers, this could be caused by water ingress into one of the controller connectors. Water can cause the CAN lines or other signals to short, disrupting communication and leading to high-voltage loss.

Solution:
Dry out any affected controllers and seal them properly. Inspect the wiring harness and controller to ensure that the waterproof rating meets specifications.

Short Circuit or Open Circuit in the CAN Line Causing Communication Failure and High-Voltage Loss

Troubleshooting:
Measure the resistance between the CAN_H and CAN_L lines. If the resistance is 0, there is a short circuit; if the resistance is infinite, there is an open circuit.

Solution:
Locate the exact fault within the wiring and repair the damaged harness.

Electromagnetic Interference from High-Voltage Components Affecting CAN Communication

Troubleshooting:
Electromagnetic interference (EMI) from high-voltage components can intermittently cause high-voltage loss. Inspect the wiring and components around the key controllers (such as high-voltage boxes and all-in-one controllers) for adequate electromagnetic shielding. Ensure that the high-voltage connectors are properly shielded, and check if the shielding is properly grounded.

Solution:
If the shielding is inadequate, apply foil or grounding to prevent interference.

III. High-Voltage System Failures

Main Contactor Sticking in the High-Voltage Distribution Box or All-in-One Controller

Troubleshooting:
Examine fault messages and check the contactor feedback status. If a main contactor is stuck (e.g., the positive or negative main contactor), this is likely the cause of the failure. Investigate whether the sticking is due to software misreporting or a hardware malfunction.

Solution:
Determine whether the issue is caused by a software bug or a hardware failure. Repair or replace the faulty component as necessary.

Low Insulation Resistance in the High-Voltage System Triggering High-Voltage Loss

Troubleshooting:
Review fault messages, as insulation faults typically trigger fault codes. Measure the insulation resistance between the high-voltage terminals and the ground. If normal insulation is confirmed after disconnecting a component, the issue lies within that component.

Solution:
Water ingress in high-voltage components or connectors is a common cause of insulation faults. Replace any faulty components and investigate the cause of water ingress.

IV. Faults Leading to Serious Safety Incidents

BMS Detecting High Battery Temperature and Triggering Fire Alarm

Troubleshooting:
If the BMS triggers an overheating alarm, this should appear on the instrument panel. Check if the alarm is a result of software misreporting or if a fault in the battery pack is causing excessive heat, which may pose a fire risk.

Solution:
If misreporting is found in the BMS software, optimize the program. If the issue is due to a battery fault, disassemble the pack and identify the cause of the overheating, then carry out the necessary repairs.

PTC Overheating Fire Alarm Triggering High-Voltage Loss

Troubleshooting:
A PTC (Positive Temperature Coefficient) overheating alarm is displayed when the thermal management system detects excessive heat, which could lead to a fire. Investigate the VCU or thermal management controller for misreporting, or check for a faulty relay causing the PTC to overheat.

Solution:
If the issue is misreporting by the VCU or thermal controller, optimize the software. If the relay is faulty, disassemble the all-in-one controller, check the PTC relay, and repair or replace it as needed.

V. Loss of VCU Wake-Up Signal

Key “ON” Signal Loss, Causing VCU to Fail to Receive Wake-Up Signal

Troubleshooting:
If high-voltage drops after the key “ON” signal is lost, check the wiring from the key switch to the VCU. A loose or poorly connected wire may be the cause.

Solution:
Inspect the wiring for any short circuits, poor connections, or loose connections. Repair as needed.

Charging Wake-Up Signal Loss, Causing High-Voltage Loss

Troubleshooting:
A loss of the charging wake-up signal can also trigger high-voltage loss. This may be caused by issues in the wiring or a faulty relay between the charging station and the VCU.

Solution:
Inspect the wiring between the charging station and the VCU, and check for any issues with the relay. Repair or replace any faulty components.