When your electric vehicle suddenly lights up the lightning symbol and the dashboard jumps out of the red warning of "high voltage insulation failure", the instant panic and bewilderment, I believe that every new energy owner has a deep understanding.
High-voltage insulation failure seems professional and complex, but it is directly related to driving safety and vehicle performance-it may cause the car to suddenly lose power, charge for no reason, and even cause more serious safety risks.
But don't worry, identifying and troubleshooting insulation faults isn't a daunting technical challenge.
This article will take you step by step to disassemble the core of the problem with the most intuitive signal interpretation, the highest frequency of fault component analysis, and standardized safety operation process. Whether you are a car owner, a maintenance novice or a technology enthusiast, you can get started quickly and deal with it calmly.
High-voltage insulation fault refers to the current leakage or short circuit caused by the failure of insulation materials in high-voltage electrical system.
Here, the steps of identification and detection of "insulation fault" can be followed to get started quickly and avoid safety risks.
Step 1: Find out-what signals indicate "insulation problems"?
Insulation failure is not "hidden", the car will take the initiative to give you "tips", first remember the three most intuitive signals, can be the first time to judge "the probability is insulation failure":
1. Core signal: the vehicle is "not electrified"
This is the most obvious performance-the car key is turned to on gear, the instrument does not light up the high voltage light, or the start button does not respond, or even directly displays "unable to get on the high voltage".
For example, when the vehicle is completely unable to drive, the diagnostic computer is used to read and report "high-voltage insulation failure" directly, which is a typical insulation problem leading to the locking of the high-voltage system.
2. Instrument prompt: "lightning symbol" or fault code appears.
A lightning-shaped fault lamp pops up on the instrument (the icons of different models are similar, which are all warnings of high-voltage system);
When the diagnostic computer reads the data stream, it will be clear that such fault codes as "high voltage insulation fault" and "low insulation resistance" will appear, which is the "first clue" to lock the fault.
3. Abnormal function: charging/power/air conditioning problems
Insulation failure will affect the function of high-voltage components, and in these cases, we should also think about "insulation":
- Interruption of charging: After the charging pile is plugged in, the charging stops after a while, and it is useless to restart;
- Power failure: no strength to step on the accelerator, or even sudden loss of power during driving;
- Failure of air conditioner: the fault will be reported as soon as the air conditioner/heater is turned on, and the fault light will go out when it is turned off.
Step 2: Check the 4 high-frequency fault components, and remember the corresponding characteristics.
When you know it's an insulation fault, you don't have to look for it! 80% of the problems lie in these four components, which can be quickly narrowed down according to the corresponding check of "component + feature":
| High frequency fault component | Identifiable feature | Common causes |
|---|---|---|
| Battery pack | 1. Sudden drop in endurance (for example, it used to run 300 km, but now it is only 200 km); 2. After opening the battery pack, there are water droplets inside and leakage of the battery core (liquid corrodes the insulation layer); 3. The battery has been repaired before (for example, the module has been replaced), and the seal is not done well. | Poor sealing of the shell, water ingress, leakage of the battery core, aging of the busbar insulation support |
| High voltage harness | 1. The fault light is "sometimes on and sometimes off", and it is more frequent when walking on bumpy roads and crossing speed bumps; 2. Look at the wiring harness of the chassis: it is worn (the insulation skin is broken due to friction with the body), and the joints are oxidized and rusted (especially where the chassis is easily hit by gravel). | Wear of harness, water ingress/oxidation of connector |
| Motor controller/on-board charger | 1. Sudden interruption of power (no response when stepping on the accelerator); 2. Unable to charge (no current after insertion); 3. There are signs of water leakage inside (the cooling system leaks into the high pressure area) | Capacitor aging, PCB board dampness, cooling system water leakage |
| A/C compressor/heater | The fault is reported as soon as the air conditioner/heater is turned on, and the fault disappears after it is turned off. | The insulation sleeve of the high-voltage terminal is damaged and the insulation layer of the internal coil is aged. |
Step 3: Learn to detect-3 steps of standardized operation, safety first
After identifying the suspicious parts, it is necessary to use tools to detect and confirm them. Newcomers must remember:
The voltage of the high-voltage system is extremely high (usually above 300 V), so safety protection must be done before operation, and the high-voltage terminal must not be touched directly
Premise: Safety preparation is indispensable.
- Wear insulating clothes, insulating shoes and insulating gloves (the insulation level shall meet the requirements, such as 1000V);
- Power off the vehicle first (disconnect the negative electrode of the low-voltage battery and the high-voltage maintenance switch), and wait for more than 5 minutes (discharge the residual electricity of the capacitor);
- Use the electroscope to confirm that there is no electricity in the high-voltage components, and then start the test.
Step 1: Preliminary inspection of the whole vehicle-measure the "key high-voltage components" with the insulation meter
Check the insulation resistance of the air conditioning compressor, MCU motor controller, motor and OBC on-board charger with a common multimeter to see if they meet the standard (different manufacturers have different requirements, usually the qualified value will be marked with "250 qualified", if it is lower than this value, there will be problems):
For example, when testing the motor, if the insulation resistance of the three buses is only 0.001 megohm (far below the qualified value), it can be basically judged that it is the internal insulation fault of the motor (oil or water may enter the interior, causing the insulation problem of the motor, and the vehicle detects the insulation problem, so the high voltage can not be applied).
Step 2: Battery Pack Scrutiny-Focus on "Sealing and Internal Status"
If there is no problem with the vehicle parts, check the battery pack:
- First measure the insulation value of the high-voltage plug of the battery pack. If it fails to meet the manufacturer's requirements, open the battery pack;
- Visual observation: whether there are water drops, leakage of the battery core, and damage of the copper bar insulation layer of the wiring harness;
- Measure the insulation resistance of the internal harness and busbar of the battery pack with an insulation meter to confirm the fault point (for example, after the module of a vehicle is repaired, the sealing is not done well, and water droplets are accumulated inside, which is a typical sealing problem leading to insulation failure).
Step 3: BMS Troubleshooting-Finally, confirm whether the detection system is abnormal.
If the battery pack is OK, check the battery management system (BMS):
- Because the "insulation detection function" of most vehicles on the market is controlled by BMS, if the BMS insulation acquisition is abnormal, it will also misreport the fault;
- Test method: Read the BMS data stream with the diagnostic computer to check whether the collected value of insulation resistance is consistent with the actual measured value. If not, replace the BMS and retest.
Important Reminder
- Do not skip the "power-off discharge": even if there is no response, there may be residual electricity in the capacitor, which will cause electric shock if touched directly;
- Do not judge by "experience": for example, if you see that the battery pack does not leak, you must use an insulation meter to measure the value, which is the hard standard;
- Remember "sudden drop vs slow drop": "sudden drop" of insulation value (suddenly change from qualified to very low) is likely to be physical damage (water ingress, damage), "slow drop" (slowly decrease) may be aging (oxidation of insulation layer), and targeted investigation is faster.
High-voltage insulation failure is a headache, but it is not a mystery.
By capturing key signals such as "no high-voltage power supply", "lightning symbol alarm" and abnormal function, locking the four high-frequency fault components of battery pack, high-voltage wiring harness, motor controller and air conditioning compressor, supplemented by a standardized and safe insulation detection process, you can solve the problem systematically and efficiently.
Remember, safety always comes first --- powering down, wearing insulation, and relying on data rather than experience are insurmountable red lines in operations.
I hope this guide will help you clear up the fog and deal with the insulation failure of electric vehicle more calmly and safely.