Chapter 33 Hybrid Drive Systems Diagnosis and Repair 649
Copyright by Goodheart-Willcox Co., Inc.
Some hybrids have an auxiliary 12-volt system and an
HV system. Vehicles with an auxiliary system can often be
jump started with a 12-volt battery. However, never try to
jump start the HV battery pack with a 12-volt booster bat-
tery, or the booster battery could explode!
Battery Pack Testing
To check HV battery pack performance, connect a
scan tool to the diagnostic connector on the vehicle and
test drive the hybrid. Watch the combination meter in the
dash as you accelerate and brake. Also, use regenerative
braking to try to recharge the battery pack.
The combination meter and scan tool will indicate
battery pack state of charge (SOC) as a percentage of total
charge. They will also show battery voltage, current draw,
and recharge current.
Hybrids often keep their battery pack SOC at approxi-
mately 80%. If the battery pack SOC drops below a preset
level, the battery ECU signals the hybrid ECU to start the
engine and use the motor-generator until the generator is
up to almost full charge.
When test-driving the hybrid in the electric mode, it is
best to drive up a small hill. This will increase load on the
motor-generator and draw more current from the battery pack.
Compare battery performance to that of a known good battery
or to specifi cations. If the battery pack will not take or hold
a charge or output enough current for a suffi cient amount of
drive time in the all-electric mode, replace the battery pack.
If the battery pack SOC goes down too quickly when
driving in the all-electric mode, the battery electrolyte and
plates have probably deteriorated due to prolonged service.
If onboard diagnostics and your test-drive indicate poor
battery capacity, the entire battery pack must be replaced.
Battery modules should not be replaced individually. If one
module has failed, others are probably weak and ready to fail.
If your scan tool indicates high battery temperature,
use an infrared thermometer to compare cell temperatures.
The use of an infrared thermometer will help prevent elec-
trocution, as it does not have to contact the battery directly.
If only one cell runs warm, it is probably shorted and the
battery pack must be replaced. If all the battery cells are
warm, a battery cooling system problem may exist.
If an air cooling system is used, check for a blower
motor circuit problem or a mechanical problem. If the
fan comes loose from the blower motor, it will not set a
trouble code. Blocked or damaged intake air ducts also cre-
ate problems. The vehicle owner may have inadvertently
placed objects over the battery air intake vent. Ductwork
can also be damaged and restricted during a collision.
Caution: When measuring high-voltage
levels in a gas-electric hybrid drive, use a
high-voltage VOM with thickly-insulated test
leads. If you use a conventional VOM and test leads,
they can be damaged by the high current in the
hybrid drive system.
Battery Pack Replacement
Hybrid battery packs are usually located in the trunk
area or under the rear seat cushion or fl oor pan, Figure 33-6.
The most common reason for HV battery pack replacement
is physical damage. A severe collision can damage the bat-
tery pack elements and short them together by penetrating
the battery cell isolators. The battery pack electrolyte is an
alkaline gel that surrounds the battery plates. This gel will
not leak out of the battery even if the case is broken.
To begin battery pack removal, remove the interior trim or
carpet over the battery. Unfasten the metal cover and any duct-
work that prevents battery pack removal. This will expose the
battery pack, power relays, and other units. See Figure 33-7.
While wearing insulated rubber gloves, remove the large
nuts or fasteners that secure the high-voltage power cables
to the battery pack. To prevent a high-voltage short, wrap
electrical tape around the metal terminals on the ends of the
orange power cables. You do not want them to accidentally
contact anything and conduct high-voltage electricity.
To remove a battery pack, unbolt it from the vehicle as
required. Then use an engine crane or have someone help you
lift the battery out of the vehicle. The battery pack should be
handled carefully since it contains a tremendous amount of
stored electrical energy and can be very heavy. A hybrid battery
pack can weigh over 200 pounds (90 kg). Make sure your helper
is wearing eye protection and thick rubber insulated gloves.
Place the battery pack on a wooden pallet for ship-
ment to an authorized recycler. Cover the battery pack with
Figure 33-6. HV battery packs are normally located in the trunk
area or under the rear seat cushion. Remove the rear seat or
trim panels to gain access to the battery pack. (Toyota)
Rear Seat
HV Battery
Module
Seat Rails