• A parallel hybrid uses both the internal engine and
a motor-generator to apply torque to the drive train.
• The series/parallel hybrid combines the advan-
tages of both the parallel hybrid and the series
hybrid. It can recharge the HV battery even when
the electric motor is used to drive the vehicle.
• A typical full hybrid drive system has five basic
modes of operation: all-electric drive mode, motor-
assist mode, regenerative braking mode, engine
starting mode, and battery pack recharging mode.
• Most hybrids use two voltage systems: a high-
voltage (HV) system for the electric drive system
and a 12-volt system for most of the vehicle’s
conventional electrical/electronic components.
• The hybrid battery pack normally consists of high
efficiency NIMH (sealed nickel metal hydride)
battery modules stacked in a sealed enclosure.
• A hybrid motor-generator functions as both a
powerful traction motor and as a high-energy
alternator in the vehicle’s power train.
• The hybrid power control module consists of a set
of electronic circuits that alter current and route it
between the HV battery pack and motor-generator.
• Battery relays and contactors are used to control
the flow of electricity between the battery pack
and the power control module.
• The hybrid drive ECU controls the power control
module and motor-generator to keep the HV bat-
tery pack operating at the optimum temperature
and state of charge.
• A hybrid power splitter is a planetary gearset used
to control the transfer of power through the
hybrid drive train.
• Hybrid power cables transfer extremely high-
voltages to the components of the electric drive
system. The power cables are heavily insulated to
prevent these voltages from shorting to ground.
• Modern gas-electric hybrid drive systems generate
enough electrical energy to cause electrocution.
• A high-voltage disconnect is provided on a gas-
electric hybrid to physically disconnect the bat-
tery pack from the power control module.
• Hybrid vehicles have extensive on-board diag-
nostic systems that will help you locate the source
of system problems
• The most common reason for battery pack
replacement is physical damage.
• A lack of normal air or coolant flow can cause
power control module overheating, which will set
trouble codes.
• When a scan tool shows a problem with a particular
component but the component tests good, check for
wiring problems in the corresponding circuit.
Important Terms
Review Questions—Chapter 38
Please do not write in this text. Place your answers
on a separate sheet of paper.
1. Hybrid vehicles use ______ power sources com-
bined into one power train to provide energy for
propulsion.
2. Hybrids can often be identified by ______ on the
vehicle’s front fenders, hood, or engine cover.
3. List the six major assemblies found in a gas-
electric hybrid drive system.
4. Explain the difference between a full hybrid and
a mild hybrid.
5. In a(n) ______ hybrid, the internal combustion
engine has no mechanical connection to the
drive train.
720 Section 5 Electrical Systems
Hybrid vehicle (HV)
Hybrid gas-electric
vehicle (HGEV)
Full hybrid
Mild hybrid
Series hybrid
Parallel hybrid
Series/parallel hybrid
Plug-in hybrids
Regenerative braking
Hybrid high-voltage
system
Hybrid nominal output
voltage
Hybrid maximum
voltage
Hybrid low-voltage
system
Hybrid battery pack
Battery pack cover
Battery pack
temperature sensors
Motor-generator
Synchronous
Power control module
Converter circuit
Inverter circuit
Motor-generator ECU
Battery relays
Contactors
Hybrid drive ECU
Power splitter
Hybrid power cables
Hybrid ground fault
interrupter
Impact sensors
Inertia switches
High-voltage fuse
Hybrid water cooling
Hybrid air cooling
Hybrid refrigerant
cooling
Hybrid power display
Hybrid drive ready
light
Hybrid master warning
light
Battery pack warning
light
Malfunction indicator
light
High-voltage buffer
zone
High-voltage disconnect
Hybrid battery charger
Battery pack state of
charge