Don't Let Your Technicians Get Fried

Maintenance needs for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs) and all-electric vehicles (EVs) are similar to those of conventional vehicles. However, hybrid/electric vehicles have high-voltage electrical systems that range from 100V to 600V. Consequently, servicing them requires some particular precautions.

Before attempting to perform service operations on any hybrid/electric vehicle, technicians should be fully trained in high-voltage service work, advise subject matter experts (SMEs) at CDX Automotive ( “Once they are trained, the most important rule technicians need to remember is this: Never work on a high-voltage vehicle without first notifying someone who is trained in dealing with high-voltage electrocution,” they say. “There needs to be a responsible person in the work environment to check on technicians as they work around high voltage.”

The SMEs also stress that technicians need to always read the manufacturer’s service information for the vehicle they are about to service. The service information will instruct them in how to properly follow all safety procedures.

CDX Automotive, a division of Jones & Barlett Learning, is the world’s leading provider of interactive and experiential automotive curriculum for light vehicle, medium and heavy truck and bus technician training. Jones & Bartlett Learning ( is a world-leading provider of instructional, assessment and learning-performance management solutions for the secondary, post-secondary and professional markets.


The matter of servicing electric vehicles safely is to be taken seriously since high voltage can easily and quickly kill you. If you have any doubts, just think of the purpose of an electric chair. That should help everyone keep a safe mindset.

While there are many safety features built into hybrid/electric vehicles to help reduce the possibility of accidental shock, shops that decide to venture into servicing high-voltage vehicles should be prepared to spend some money on safety equipment, the SMEs say. This is no time to pinch pennies.

Some of the standard equipment for servicing high-voltage vehicle systems includes:

  • OEM or equivalent scan tools.
  • A high-quality (three-phase CAT III or CAT IV) digital volt-ohmmeter (DVOM) with appropriate high-voltage leads.
  • Insulated gloves rated for 5,000V and certified to 1,000V (Class 0), as well as approved glove covers. The gloves need to be visually inspected and air tested for any possible defects (for example, cuts, holes, tears, embedded objects, changes in texture, etc.) before each day’s use and whenever there is a reason to believe they may have been damaged.
  • Safety cones and safety tape to mark off service areas, and other such items.
  • A retrieval hook in case someone becomes disabled from electrical shock.

If you decide to service hybrid/electric vehicles, get the proper training on the high-voltage areas, as well as a full understanding of how they operate, recommend the SMEs. Make sure technicians stay alert and continually practice situational awareness.


Besides the high-voltage dangers of a hybrid/electric vehicle, there are other precautions that technicians need to be aware of. Because all hybrid/electric vehicles are designed to operate uniquely, there are safety precautions specific to each vehicle model.

One of the first safety precautions is that the vehicle should be completely powered down before working on it. The reason being: the internal combustion engine (ICE) can start at any time the vehicle’s powertrain control module (PCM) deems necessary.

Never assume that the vehicle is turned off because it is silent or still, CDX Automotive SMEs stress. The vehicle may appear to be turned off because the ICE has been shut down and the vehicle is silent, but the system can still be in “ready” mode (most vehicle models show this on the vehicle dash display panel), capable of engaging the ICE or the drive motor at any moment.

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.