Hybrid vehicles are becoming more common sight on roads today thanks to the popularity of their gas-saving powertrains. In hybrids like the Toyota Prius and Ford Escape, the car starts out in a full electric mode to save gas, then starts the engine and switches to gasoline mode when the vehicle reaches a certain speed. The electric motor can also work in tandem with the gasoline engine to provide a boost in power when passing.
Other hybrids, such as the Saturn View and Honda Civic, do not have a full electric mode. Instead, they use their hybrid battery and electric motor primarily for the engine start/stop system that saves gas when the vehicle is stopped in traffic, or to boost engine power when accelerating or passing.
Though hybrids get better fuel economy than conventional vehicles, they also present some unique hazards when they are involved in an accident or when they have to be serviced or repaired. The high voltage hybrid battery and hybrid powertrain components create a potential shock hazard. We haven't heard of anyone actually being electrocuted while working on a hybrid, or while being extracted from a wrecked hybrid, but the danger is real. Consequently, certain precautions must be used when working on a hybrid car or truck.
As a rule, hybrids that have a full electric driving mode use higher voltage batteries than those that do not have a full electric mode. The battery pack in the Honda Insight and Civic Hybrid at rated at 144 volts. The 1st generation 2001-2003 Toyota Prius battery is rated at 273.6 volts while the 2nd generation 2004-2008 Prius is rated at 201.6 volts. The Ford Escape Hybrid has the most potent battery of all, rated at 330 volts! By comparison, the battery in the Saturn Vue hybrid is rated at 36 volts.
The voltage in most hybrid batteries can deliver a lethal shock, much like that of an electric chair. What's more, the voltage from a hybrid battery is Direct Current (DC), which carries more of a wallop than Alternating Current (AC). The threshold voltage where DC becomes dangerous can be as low as 55 to 60 volts, compared to 110 volts for AC. Ordinary 12 volt DC car batteries and electrical systems pose no danger, but the high voltage secondary ignition system can give you a nasty shock (though the current is usually too low to cause serious harm).
So are hybrids truly dangerous? Not if you treat them with respect, are aware of the potential shock hazard, and follow the recommended safety procedure when working on one of these vehicles.
High voltage cables in hybrid vehicles are usually color-coded to warn you of their potential danger. On most, the high voltage cables are color-coded ORANGE. On the Saturn, with its 36-volt system, the cables are color-coded BLUE. Avoid contact with these cables unless the high voltage battery in the back of the vehicle has first been disconnected.
All hybrid batteries have a safety switch or disconnect mechanism to disconnect the battery from the vehicle's electrical system. The location of the battery disconnect safety switch and the disconnect procedure will vary from one application to another, so refer to your owner's manual or service literature for the specifics.
You should wear heavy rubber Class 00 rated gloves that can withstand up to 1000 volts. Ordinary latex or neoprene shop gloves are not thick enough and do not provide enough insulation to protect you from a high voltage shock. You should also inspect your gloves to make sure they do not have any pin holes, cracks, tears or splits that would allow voltage to find your skin.
Another often overlooked precaution is to make sure the ignition is OFF and the key or key fob is away from the vehicle before it is serviced or repaired. Make sure the READY light is not on. If the power is on, the high voltage system is live and poses a shock hazard should you come into direct contact with any of its uninsulated electrical components (such as the inverter under the hood).
Another suggestion is to wait 15 minutes before working on the vehicle after the battery has been isolated or disconnected. The high voltage capacitors inside the inverter need time to bleed off their stored power.
On the first generation Prius, the hybrid battery is disconnected by opening the trunk, removing the liner from the left front corner, and pulling straight back on a small orange handle to remove the plug. The plug should be removed from the car until it is time to reconnect the battery.
On a 2004 and up Prius, Toyota says to first disconnect the negative cable on the conventional 12-volt battery (which is also located in the trunk). Remove the trunk floor panel and cover, disconnect the 12-volt battery, then locate the service plug on the left side, and pull the handle down and out to remove the plug (wear insulated gloves when doing this). If you have to remove or replace the fuse, it is located right under the service plug and is held in place by two bolts. Again, wear insulated gloves. When the service plug is replaced, make sure the handle is returned to the upright position to lock the plug in place, otherwise a loose plug may set battery codes.
On a Honda Civic hybrid, the battery is disconnected by removing the rear seat back cushion, removing two screws from a small cover with the word "UP" on the cover, the flipping the power switch DOWN to the OFF position.
Put the shift lever into Park and remove the ignition key. This will turn off the hybrid system, but not totally isolate the hybrid battery in the back of the vehicle. To totally isolate the high voltage hybrid battery, open the tailgate, pull back the carpeting on the floor, and locate the round disconnect switch on the top of the hybrid battery. With rubber gloves on, turn the switch COUNTERCLOCKWISE then lift out the switch plug to totally disconnect the battery.
If you are working on a Toyota Prius and forget to push the "Power" button to turn the car off or remove the key, the hybrid powertrain will still be hot even though the engine may not be running. At stop, the vehicle reverts to an electric-only mode of operation, shuts off the gasoline engine and makes no noise. Meanwhile, the engine control module continues to monitor the voltage of the hybrid battery, and may automatically restart the engine if the hybrid battery voltage is low and the engine needs to run to recharge it. That could mean a nasty surprise for you if you happen to be working under the hood, changing the oil or doing anything else that puts you in close proximity to belts, pulleys or high voltage components.
Most hybrids have some kind of "Ready" indicator light on the dash to let the driver know when the hybrid system is on. So always make sure the Ready light is out, the ignition is off and the key is out of the vehicle before you start any service or repair work. Removing the key from the vehicle is especially important if the vehicle has a keyless entry system and recognizes the key fob anytime it is in close proximity to the car. Keep the keyless fob at least 20 feet away to prevent any accidental starts.
Most hybrids are designed to isolate the high voltage battery if the vehicle is involved in an accident that is serious enough to deploy the air bags. On the Prius, the high voltage battery and wiring circuits are separate from the other electrical circuits in the vehicle, and do not use the body or chassis as a ground. The Prius has a ground fault sensor that will disconnect the hybrid battery and turn on a warning light (an exclamation mark inside a triangle) if it detects any high voltage leakage to to the body. A DTC P3009 fault code would indicate such a problem on the Prius.
The good news is that nobody has yet been injured or electrocuted by a hybrid electric vehicle. An extensive search of news archives failed to turn up any reports of service technicians, emergency responders or motorists being zapped by a high voltage hybrid. Let's hope it stays that way.