What Is HVIL?

HVIL, or high-voltage interlock loop, is a safety feature of hybrid and all-electric vehicles that protects people during the assembly, repair, maintenance and operation of a vehicle. The HVIL system is designed to protect anyone who might come into contact with high-voltage components of an electric vehicle at any stage in its lifecycle.

HVIL is not necessary in gas-powered vehicles because their electrical systems operate at low voltages and pose no risk to operators and service technicians. But hybrid and electric vehicles include subsystems of batteries, wires, adapters and controllers that operate at higher power levels and therefore require additional safety features.

HVIL acts as a kind of circuit breaker that sends an alert or trouble code to the driver if a high-voltage connection becomes loose, disconnected or damaged during the operation of the vehicle. HVIL also helps protect a vehicle’s driver and passengers in the event of an accident.

How does HVIL work?

HVIL uses a continuous, low-voltage loop that monitors all high-voltage connectors and components in an electric vehicle (EV). If the low-voltage HVIL signal is interrupted for any reason, it indicates that there is an issue with the high-voltage system that should be addressed.

When an HVIL circuit fails, a diagnostic trouble code is triggered and an alert appears on the vehicle’s control panel to let drivers know they should bring the vehicle in for service. The trouble code also provides information for service technicians on the nature of the problem so the technicians can avoid any safety-related issues.

Part of a complete safety solution

HVIL is just one aspect of a comprehensive approach to the safe use of electricity in an EV. There are thousands of connection points inside a typical EV. If any one of them malfunctions, the results can range from a minor inconvenience to a major, life-threatening problem.

High-voltage connectors throughout the vehicle also provide finger-proof, touch-safe two-step disconnection technologies to guarantee optimum safety during all handling operations. These measures make it impossible for someone to touch any internal portion of the metal electrical contacts, which protects a consumer or a service technician who might accidentally touch an open connection.

Fuse-in connectors and other innovative technologies ensure that if a spike in current reaches a potentially dangerous level, the battery will disconnect from the rest of the car and the charger, thus eliminating any potential for a catastrophic event.

Another way to lower risk, even when voltages grow higher, is to exceed the highest safety specs set by OEMs. Most specs cover vehicles in the 600V-to-750V range, but Aptiv designs its products for 1,000 volts.

HVIL technology is important, but it is also important for OEMs to look at HVIL in the larger context of a hybrid or all-electric vehicle that is built to the latest safety and performance standards across the entire electrical infrastructure.