must be followed during servicing. Always determine
whether or not a vehicle is a hybrid before servicing its
engine. Look for badging on the front fender, engine cover,
or hood. The power control module, if in the engine com-
partment, is normally labeled and will have large orange
power cables going to it, Figure 5-20.
Towing Hybrids
When towing a hybrid vehicle, the drive wheel
engaged to the motor-generator should be raised off the
ground. This is because, on some hybrids, spinning the
wheels and axles can cause the motor-generator to pro-
duce high voltage, which can be both dangerous and dam-
aging to the drive system. Front-wheel drive hybrids
should have the front wheels raised off the ground. All-
wheel drive hybrids should have all four wheels raised.
Hybrid Voltage
Modern gas-electric hybrid drive systems have
enough electrical energy to cause electrocution. Most
hybrid vehicles conduct 3-phase AC at almost 600 volts
and almost 300 volts DC at hundreds of amps. By compar-
ison, the voltage at a home wall outlet is 120 volts AC. Yet
many people are killed or injured each year by that voltage.
The 240 AC fed into a repair shop operates high-power equip-
ment (air compressors, central air conditioning, furnaces, vehi-
cle lifts, etc.). If shorted to ground, 240 volts causes a powerful
electric arc. Since hybrids operate at even higher voltage lev-
els, it is important to respect the potential for electric shock.
Remove all jewelry when working on a hybrid’s high-
voltage circuits. If metal objects come near or touch a source
of high voltage, serious burns or electrical shock can result.
Clothing
Wear thick rubber gloves rated for 1000 volts when
working on hybrid high-voltage cables and other high-volt-
age components. Such gloves, called lineman gloves, will
insulate your body from high voltages. Periodically inspect
your gloves for tears or splits, especially in the fingertips.
Leaking, worn, or otherwise damaged gloves should be
thrown away and replaced by new gloves.
Wear safety glasses or goggles when working on
hybrids. In the instance of a short to ground, a violent elec-
tric arc will result. The metal end of the shorted cable will
vaporize, shooting out molten metal. If this metal gets in
your eyes, you can suffer serious eye injuries.
Wear rubber-soled shoes when working on hybrids.
Rubber soles will insulate your body from earth ground
(conduction of electricity into shop floor).
Disabling Hybrid Drive
A hot hybrid system is one in which high and low
voltage are potentially present in the electric drive system.
You cannot turn off the power inside the battery pack, but
you can disconnect it from the rest of the drive system.
To disable a gas-electric hybrid for repair, turn the
ignition key off. This will cause the hybrid ECU to de-ener-
gize the relays or contactors that connect the battery pack
to the system. The ECU then verifies the relays or contac-
tors are open, preventing current flow from the battery
pack to the motor-generator. Some automakers also require
disconnection of the conventional 12V battery, to prevent
accidental energizing of the high-voltage circuits.
System de-energization is important because a hybrid’s
drive train can be engaged and ready to accelerate even with-
out the gas engine running. If the key is in the on position, the
vehicle can accelerate and drive forward or backward if the
gas pedal is pressed accidentally. Such movement could result
in personal injury and property damage.
High-Voltage Disconnect
The high-voltage disconnect provided on gas/electric
hybrids disconnects the battery pack from the power
120 Auto Engine Repair
Engine Hybrid power control module
High voltage cables
Figure 5-20. Hybrid vehicles normally have badging on the
body or in the engine compartment. This hybrid identifies the
hybrid power control module on one side of the engine. (Toyota
Motor Company)
Figure 5-19. Always read label directions before using any
shop chemical.