646 Auto Electricity and Electronics
Copyright by Goodheart-Willcox Co., Inc.
leaks air, it can also leak voltage. If your gloves are worn or
damaged, discard them and purchase new ones.
Wear Rubber-Soled Shoes
Since the voltages are so high in a hybrid, you
should wear shoes with rubber soles when working on
hybrid vehicles. Rubber soles help insulate your body
from earth ground, preventing high voltage from arcing
out of the high-voltage conductors and into your body
while seeking earth ground (conducting of electricity
into the shop fl oor).
Keep a Fire Extinguisher Nearby
Always keep a class A, B, C fi re extinguisher near the
work area when servicing hybrids. A high-voltage electrical
short can cause a serious electrical fi re. If fi re starts, shut off
the main contactor or switch for the HV battery pack and
then put out the fi re with a fi re extinguisher.
Follow Towing Safety Procedures
With some hybrids, spinning the wheels and axles
will cause the motor-generator to produce high voltage,
which can be dangerous and may damage the drive sys-
tem. Therefore, when towing or moving a hybrid vehicle,
the drive wheel engaged to the motor-generator should
be raised off the ground. For example, if towing a front-
wheel drive hybrid, the front wheels should be raised off
the ground. If you are towing an all-wheel drive hybrid
with motor-generators at the front and rear, all four wheels
should be raised.
Disable the Hybrid Drive When Working
A “hot hybrid” system is one with high and low voltage
still present in the electric drive system. Although you cannot
turn off the power stored inside the HV battery pack, you can
disconnect it from the rest of the hybrid drive system.
To disable a gas-electric hybrid for repair, you must fi rst
turn the ignition key off. This will cause the hybrid ECU to
de-energize the relays that connect the battery pack to the
rest of the system. Some automakers also require that you
disconnect the conventional 12-volt battery to help prevent
the high-voltage circuits from accidentally being energized.
Disabling the system is important because a hybrid’s
drive train may be engaged and ready to accelerate even
without the internal-combustion engine running. If you leave
the key on in a hybrid and the shift lever is in gear (drive
or reverse), the vehicle can be propelled forward or back-
ward by the motor-generator if you accidentally press the
accelerator. This could cause the vehicle to lunge forward or
backward and ram into a shop wall or over coworkers.
Note: If a hybrid is in a severe collision, the
hybrid drive system will automatically
disable the high-voltage drive. Many
systems will disable the HV battery pack and
generator when the air bag deploys.
Set Up a High-Voltage Buffer Zone
When working on a gas-electric hybrid, set up a high-
voltage buffer zone of about 3 feet (1 meter) around the
perimeter of the vehicle. You do not want steel work benches,
large metal equipment, coworkers, or any other potential
conductors of electricity in the buffer zone. Take the time to
move objects or park the hybrid vehicle away from potential
conductors. If you back your body into a good conductor,
such as a steel work bench, and your arm is touching a source
of high voltage, you could be electrocuted or severely injured
as the voltage travels through your body to ground.
Remove the High-Voltage Disconnect
A high-voltage disconnect is provided on a gas-
electric hybrid to allow the HV battery pack to be physi-
cally disconnected from the power control module. Refer
to Figure 33-4.
With many hybrids, you must pull out the disconnect
to produce an open circuit between the battery pack and
the power control module. With other designs, you might
have to rotate a high-voltage disconnect switch to provide
an open in the battery pack circuit.
Hybrid high-voltage disconnects are usually located
near the HV battery pack in the trunk, under the seat, on
the side of a seat under a trim panel, or in other similar
locations. Refer to factory service literature for details.
Figure 33-3. Learn to respect the power of a hybrid electric drive
system. Wear thick rubber gloves to insulate your skin from the
high voltages in a hybrid drive system. (Toyota)