What steps should you take to safely de‑energize an EV high‑voltage system before service?

• A. Just turn off the car ignition.
• B. Locate the high‑voltage service disconnect, switch it OFF per OEM procedure, remove the key, apply lockout/tagout, and verify zero voltage with a rated HV detector before touching components.
• C. Open the hood and unplug battery.
• D. Rely on ambient disconnection.

Answer: (B)

Isolating and confirming the high‑voltage system is de‑energized before service is performed is the essential safety step. The goal is to physically remove the HV battery from the vehicle’s circuits and prove there’s no stored energy left in the system.

First, locate the high‑voltage service disconnect and switch it OFF according to the OEM procedure. This action physically isolates the high‑voltage battery from the rest of the system, stopping normal current flow.

Next, remove the key and apply lockout/tagout. Lockout/tagout prevents anyone from re‑energizing the system while work is underway, so the device cannot be turned back on accidentally.

Finally, verify zero voltage with a rated high‑voltage detector before touching any components. This check confirms there is no residual energy in capacitors or wiring that could cause a shock, even after the disconnect is opened.

Turning off the ignition alone isn’t enough because the HV system can remain energized for safety‑critical circuits. Opening the hood and unplugging a battery isn’t a reliable or standard method for safely de‑energizing the high‑voltage system. Relying on ambient disconnection offers no deliberate isolation or verification and is unsafe.