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Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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OBJECTIVES:
After studying Chapter 65, the reader should
be able to:

•
•
•
•
•

Safely depower a hybrid electric vehicle.
Safely perform high-voltage disconnects.
Understand the unique service issues related to HEV highvoltage systems.
Correctly use appropriate personal protective equipment
(PPE).
Explain hazards while driving, moving, and hoisting a
hybrid electric vehicle.

Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

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KEY TERMS:
ANSI • ASTM
CAT III • DMM • floating ground
HV • HV cables • IEC • Linesman’s gloves
NiMH • OSHA

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HIGH-VOLTAGE SAFETY EQUIPMENT
Rubber Gloves Be sure high-voltage (HV) linesman’s gloves are
available, rated at least 1,000 volts, class “0” by ANSI/ASTM.


The Occupational Safety and Health Administration (OSHA)
requirements specify that HV gloves get inspected every six
months by a qualified glove inspection laboratory. Use an outer
leather glove to protect the HV rubber gloves.
Inspect the gloves carefully before each use. High voltage and
current (amperes) in combination is fatal. See Figures 65-1 & 65-2.
WARNING: HV cables and wiring are orange in color. High-voltage
insulated safety gloves and a face shield must be worn when carrying out
any diagnostics involving the high-voltage systems or components.
Continued
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Figure 65–1
Rubber linesman’s gloves protect the wearer from a
shock hazard.

NOTE: The high-voltage insulated safety gloves must be recertified
every six months to remain within OSHA guidelines.

Figure 65–2
Wearing leather gloves over the linesman’s gloves
helps protect the rubber gloves from damage.

Continued
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Before using the rubber gloves, they should be tested for leaks
using the following procedure:

1. Roll the glove up from the open end until the lower portion
of the glove begins to balloon from the resulting air
pressure. Be sure to “lean” into the sealed glove to raise the
internal air pressure. If the glove leaks any air, discard the
gloves.
2. The gloves should not be
used if they show any
signs of wear and tear.
Figure 65–3 Checking rubber linesman’s
gloves for pinhole leaks.

Continued
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By James D. Halderman

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CAT III–Rated Digital Multimeter Hybrid electric vehicles are
equipped with electrical systems whose voltages can exceed 600
volts DC. A CAT III–certified digital multimeter (DMM) is
required for making measurements on these high-voltage
systems.
Eye Protection Should be worn when testing for high voltage,
considered by many to be anything over 60 volts. Most hybrid
electric systems use voltages higher than this threshold.
If the system has not been powered down or has not had the
high-voltage system disabled, a shock hazard is always possible.
Even when the high-voltage (HV) system has been
disconnected, there is still high voltage in the HV battery box.
Continued
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By James D. Halderman

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FIRST RESPONDER PROCEDURES
Identifying a Hybrid Vehicle To confirm whether a vehicle is a
hybrid, look for the word “HYBRID” on the rear of the vehicle.

Orange cables underhood or shielding
bolted to the underside of the vehicle,
indicates the vehicle is a hybrid.

Figure 65–4 This Honda Accord
hybrid is identified by the emblem on
the rear deck lid.
Figure 65–5 A hybrid electric vehicle can often be
identified by looking for orange-colored cables under
the hood, as well as other markings on the engine
cover.

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Except for the Honda Insight and the Toyota Prius, there is very
little difference in the exterior or interior appearance of hybrids,
compared to those of their gasoline-powered counterparts.

Power Source The main power source of all hybrids is a
conventional internal combustion engine (ICE). During start-up
and acceleration, an electric motor provides assistance to the
engine. During braking and deceleration, the motor acts as a
generator, recharging both high-voltage and the 12-volt battery.

12-Volt Battery A conventional flooded-type lead-acid 12-volt
battery, powers all standard electronics. Most are nonspillable
absorbed glass mat (AGM) designs. This battery also provides
power to the high-voltage battery control systems. Disconnecting
or cutting the negative cables to the battery may be necessary in
some emergency situations.
Continued
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Fuse Box Most hybrid electric vehicles have a fuse box in the engine compartment. Removing
the main fuse from this box

may be required in some emergency situations.
High-Voltage Battery Module The electric motor is powered by a high-voltage battery module.
Because the battery module is recharged by the electric motor whenever the vehicle decelerates
or by the generator during cruise conditions, the battery never needs external charging.
The high-voltage battery modules are often in plastic containers, and these cells are placed
within a sturdy metal box.
See Figure 65–6.

Continued
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Components in the battery box are completely insulated and
isolated from the vehicle body. Figure 65–6 A Toyota Highlander hybrid
For safety, the high-voltage
battery box is positioned behind
seat backs or under the rear seat
where it is well protected from
potential damage in a collision.

battery pack with the cover removed.

Small quantities of electrolyte,
corrosive to human tissue, are
used in NiMH battery cells.
In the finished cells, electrolyte is nonliquid, nonflammable,
nonexplosive, and creates no hazardous fumes or vapors in
normal operating conditions and is sealed in a metal case.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman

Continued

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High-Voltage Cables Electricity flows through either two or
three heavy-duty orange cables. In some hybrid vehicles, highvoltage cables also deliver current to the air-conditioning (A/C)
compressor.
High-voltage cables are routed under the vehicle inside orange
plastic protective shields. Where the cables lie close to the exhaust
system, a metal thermal shield covers, the orange shield.

Continued
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By James D. Halderman

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Airbags and Tensioners All hybrids have front airbags and seat
belt tensioners. Most have side airbags for front-seat occupants;
many with side curtain airbags. These systems use pyrotechnic
devices with a deactivation time of up to three minutes.
To reduce the risk of injury during the deactivation period, the
following steps are recommended:
• Keep out of the path of an undeployed front airbag, and do not
cut into the center of the steering wheel or dashboard where
the front airbags are stored.
• Do not cut into the rear (C) pillar where the side curtain
inflator is stored.
WARNING: Extreme heat (320–356°F [160–180°C]) can cause
unintended airbag inflation. Follow recommended procedures to avoid
possible injury from a deploying airbag or inflator.
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ELECTRIC SHOCK POTENTIAL
Unprotected contact with electrically charged (“hot” or “live”)
high-voltage components can cause serious injury or death.
Receiving an electric shock from a hybrid vehicle is highly
unlikely because of the following:
1. Contact with battery module or components in the battery
box can occur only if the box is damaged and contents
are exposed, or it is opened without proper precautions.
2. Contact with the electric motor can occur only after one or
more components are removed.
3. High-voltage cables can be easily identified by distinctive
orange color, and contact with them can be avoided.
4. The system main relays (SMRs) disconnect power from the
cables the moment the ignition is turned off.
Continued
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There are only three situations in which the cables can
potentially be “hot” in most hybrid vehicles:
1. The ignition switch is on, the engine is running, and the
vehicle is accelerating. In this case, the high-voltage battery
module is sending current to the motor. (This is not likely to
be a concern to first responders.)
2. The ignition switch is on, the engine is running, and the
vehicle is decelerating. In this case, the motor is generating
electric current and sending it to the high-voltage batteries.
3. The third situation in which the cables can be hot occurs when
the ignition switch is on, the engine has been turned off by the

auto idle stop feature, and the air conditioner is on. In this
case, the high-voltage battery module is sending current to the
air-conditioner compressor.
Continued
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By James D. Halderman

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NOTE: The only condition common to all three situations in which the
cables can be “hot” is that the ignition is on. Therefore, when the ignition
switch is off, electric current cannot flow into the high-voltage cables
because the system main relays that control the high voltage are turned off
when the ignition is off.


See the chart on Page 790 of your textbook.
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PREVENTING CURRENT FLOW THROUGH
HIGH-VOLTAGE CABLES
Before attempting to rescue occupants or move a damaged
hybrid vehicle, potential for current flow from the electric
motor or battery module through high-voltage cables needs to
be
removed.

There
are two recommended methods:
Method One Turn the Ignition Switch Off This action turns
off the engine and the electric motor, preventing current flow into
the cables. It also turns off power to the airbags and the seat belt
tensioners. Remove the key so the vehicle cannot be restarted.
NOTE: Turning the ignition key to the OFF position stops the flow of
electricity in the cables.
Continued
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Method Two Remove the Main Fuse Cut the negative 12-volt
battery cable(s). This turns off the engine and the electric motor,
preventing current flow from the motor into the cables.

This also cuts power to the airbags and the seat belt tensioners, as
well as to the high-voltage battery controllers, preventing current
from flowing into the cables from the high-voltage battery.
1. Locate the underhood fuse
box, and remove the cover
(see the owner’s manual
for fuse box locations).
Figure 65–7
The high-voltage disconnect (service) plug
is located on the left side of the rear seat in
a Toyota Highlander hybrid vehicle.

Continued
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2. Locate the main fuse by referring to the diagram on top of,
or inside, the fuse box cover. On a Honda Civic hybrid, use
a Phillips screwdriver and unscrew the main fuse assembly
and remove it from the box.

WARNING: Power remains in the high-voltage electrical system
for up to 10 minutes after the HV battery pack is shut off. Never
touch, cut, or open any orange high-voltage power cable or highvoltage component without confirming that the high voltage has
been completely discharged.

Continued
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3. Locate the 12-volt battery and cut the negative cables with
diagonal cutters. See the 12-volt battery location chart
below.

See the chart on Page 791 of your textbook.
NOTE: If neither method to stop the engine can be performed to prevent
current flow into the high-voltage cables, use extreme care, do not cut into
the cables, and do not touch damaged cables as they may be “hot.”
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Silence is Not Golden
Never assume the vehicle is shut off just because the engine is off. Always
look for the READY indicator status. The vehicle is shut off when the
READY indicator is off. The vehicle may be powered by:
1. The electric motor only
2. The gasoline engine only
3. A combination of both
The vehicle computer determines
the mode in which the vehicle operates
to improve fuel economy and reduce
emissions. The driver cannot manually
select the mode.
Figure 65–8
The Ford Escape Hybrid instrument panel showing the vehicle in Park and the tachometer on “EV”
instead of 0 rpm. This means that the gasoline engine could start at any time depending on the
state of charge of the high-voltage batteries and other factors.
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SRS Airbags and Seat Belt Pretensioners Two electronic frontal
impact sensors are mounted in the engine compartment. Front seat
belt pretensioners are mounted near the base of the B-pillar. A
frontal dual-stage driver airbag is mounted in the steering wheel.

WARNING: The SRS computer is equipped with a backup source that
powers the SRS airbags up to 90 seconds after disabling the vehicle. The
front-seat side airbags and the curtain-shield side airbags may deploy
independent of each other.

Continued
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By James D. Halderman


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High Voltage is Insulated from the Vehicle
Body
Both positive and negative high-voltage power cables are isolated from the
metal chassis, so there is no possibility of shock by touching the metal
chassis. This design is called a floating ground.
A ground fault monitor continuously monitors for high-voltage leakage to
the metal chassis while the vehicle is running. If a malfunction is
detected, the vehicle computer will illuminate the master warning light in
the instrument cluster and the hybrid warning light in the LCD display.
The HV battery pack relays will automatically open to stop electricity
flow in a collision sufficient to activate the SRS airbags.


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EMERGENCY RESPONSE
On arrival, emergency responders should follow their
standard operating procedures for vehicle incidents.
Extrication
1. Immobilize the vehicle (chock wheels and set parking brake).
2. Disable the vehicle.
3. Stabilize the vehicle. Crib at four points directly under the
front and rear pillars. Do not place cribbing under the highvoltage power cables, exhaust system, or fuel system.
WARNING: Never assume a hybrid vehicle is shut off simply because it

is silent. After disabling the vehicle, power is maintained for 90 seconds in
the SRS system and 10 minutes in the high-voltage electrical system.
Continued
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4. Access the patients. Use normal glass removal
procedures.Door removal/displacement. Doors can be
removed by conventional rescue tools such as hand, electric,
and hydraulic.
5. Door removal/displacement. Doors can be removed by
conventional rescue tools such as hand, electric, and

hydraulic.
6. Roof removal. The vehicle may contain optional curtainshield airbags. If equipped and undeployed, it is not
recommended to remove or displace the roof.
CAUTION: Responders need to be cautious when working in close
proximity to undeployed airbags and seat belt pretensioners. Deployed
front dual-stage airbags automatically ignite both stages within a fraction
of a second.
Continued
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By James D. Halderman

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