backward 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 co-workers.
Note!
If a hybrid is in a severe collision, the hybrid
drive system will automatically disable the
high-voltage drive system. Many systems will
disable the battery pack and generator when the
air bag deploys.
Create a High-Voltage Buffer Zone
When working on a gas-electric hybrid, set up a
high-voltage buffer zone of about three feet (1 meter)
around the perimeter of the vehicle. You do not want steel
workbenches, large metal equipment, co-workers, 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 workbench,
with your arm touching a source of high voltage, you
could be electrocuted or severely injured as the voltage
travels through your body to ground.
High-Voltage Disconnect
A high-voltage disconnect is provided on a gas-elec-
tric hybrid to allow the battery pack to be physically dis-
connected from the power control module. Refer to
Figure 38-23. 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 must rotate a high-voltage disconnect switch to pro-
vide an open in the battery pack circuit.
Hybrid high-voltage disconnects are usually located
near the battery pack in the trunk, under the seat, on the
side of a seat under a trim panel, or in other similar loca-
tions. Refer to the factory service literature for details.
Warning!
To prevent electric shock, wait at least five min-
utes after removing the high-voltage disconnect
before working on the high-voltage circuits. It can
take up to five minutes for any high-voltage
capacitors in the inverter circuit to discharge fully.
Note!
After you remove a high-voltage disconnect,
remove the high-voltage fuse and keep it in
your pocket. This will prevent anyone from
accidentally reconnecting battery pack power
when circuits are being serviced.
Hybrid Problem Diagnosis
Hybrid vehicles have very extensive on-board diag-
nostic systems that will help you locate the source of
system problems. The on-board diagnostic system will
monitor hundreds of operating conditions and turn on one
or more warning lights if any monitored condition is not
within specifications. Figure 38-24 shows a few of the
problems that can affect hybrid electric drive operation.
A glowing malfunction indicator light lets you know
that you should use a scan tool to retrieve stored trouble
codes. Figure 38-25 shows a hybrid drive trouble code
index chart. This chart explains what each code means
and where to go in the service information to find instruc-
tions for further testing the circuit.
Hybrid Battery Pack Service
Hybrid battery packs have a warranty from the
vehicle manufacturer. One automaker offers a full battery
pack replacement warranty for up to 8 years or 80,000
miles. Battery packs are very dependable and seldom fail.
Nevertheless, they can lose efficiency after a period of
extended service. The electrolyte and the metal plates in
the battery pack can be depleted after years of operation.
Note!
Hybrid NiMH batteries should not be stored for
long periods of time. When purchasing used
battery packs from salvage yards, find out how
long the battery pack has been in storage. If a
battery is left uncharged for over a year, the bat-
tery plates and electrolyte will deteriorate and
the battery should not be purchased. Order a
new battery pack to prevent comebacks.
Battery Pack Recharging
With some hybrids, the internal combustion engine
will not start if the battery pack is drained or dead. This
occurs when someone accidentally leaves the headlights
or other electrical accessories turned on when the vehicle
is not running.
A hybrid battery charger uses a step-up transformer
to force high voltage back into the battery pack to re-
energize it. Follow the battery charger and vehicle manu-
facturer instructions for safely connecting the charger
cables to the battery pack. See Figure 38-26. Procedures
vary with make and model hybrid. If the battery pack will
not take a full charge, it should be replaced.
If the hybrid has a 12-volt battery, you can usually
jump-start the hybrid with jumper cables and a 12-volt
Chapter 38 Hybrid Drive System Operation and Repair 711