Don't Let Your Technicians Get Fried

The need for high-voltage safety training.

If a technician is changing a belt or working around the ICE and the engine starts up, they could be injured or killed.

Prior to service, the vehicle should be in park, with the parking brake applied and the “power” button powered down, instruct the SMEs. The keyless fob, if equipped, should be more than 15’ (4.6m) from the vehicle.

What’s more, technicians should not assume that the safety precautions for an older model are the same for a newer model, and vice versa. They should always check the service information for the vehicle they are working on.


In many hybrid/electric vehicles, high voltage is used to operate a variety of accessories, such as power steering and air conditioning, so technicians need to be aware that high-voltage wires can be located nearly anywhere in the vehicle. These high-voltage wires are usually recognized by orange convolute or wiring. Some vehicles have used other colors, such as blue, to designate high-voltage wiring so technicians need to check the service information.

It should be noted that manufacturers of HEVs, PHEVs and EVs design these vehicles with safety features that deactivate the electrical system when they detect a collision or short circuit. One method uses built-in electrical leakage detectors within the insulating material on high-voltage wires that are designed to detect broken insulation or physical damage and shut down the high-voltage system.

Never pierce a high-voltage wire when testing for voltage or the technician may inadvertently shut down the system and permanently ruin the cable.

Technicians should avoid working on these high-voltage areas without first having the proper training, service information and experienced help on hand, the SMEs say. The main high-voltage battery pack must be disconnected before service is performed in or around the high-voltage components.

Every manufacturer has a different way of disconnecting high-voltage batteries from the main electrical system. However, it usually involves a service plug that is removed from near the battery or a battery module switch that is turned to the off position, both of which will disconnect the high-voltage battery from the electrical system.

As an example of disconnecting the high-voltage battery using a Third Generation Prius, CDX SMEs offer these general guidelines for technicians:

  • Locate the high-voltage battery disconnect (service plug). Release the lock, release the lever and remove the service plug. Store it in a safe place where it cannot be reinserted accidentally.
  • Wait for the specified time for the residual electricity to bleed off. This typically takes five to 15 minutes.
  • Then, verify that the system is no longer live. To do that, locate the high-voltage access panel and remove the bolts that secure the cover. Next, remove the cover and, using the correctly rated meter, measure that there is no voltage at the specified terminals.

Before disabling the high-voltage system, technicians must be wearing the appropriate personal protective equipment (PPE).


Shops and technicians must adapt and change with advancing vehicle technology. Alternative-fueled vehicles, HEVs, EVs and fuel cell vehicles are becoming much more common forms of transportation today, and will continue to grow in market share for the foreseeable future. Because of this, standard operating policies should be adopted to reflect the requirements for handling each specific powertrain type.

Technicians should be trained to at least a basic level of high-voltage service competency depending on their level of interaction with those vehicles, say CDX Automotive SMEs. Because vehicles and technology continue to change rapidly, all service personnel have an inherent responsibility to update their knowledge and skill on a regular basis.

One of the best ways to stay current on the service precautions and procedures of these vehicles is to regularly download and study each manufacturer’s emergency response guide.

We Recommend