Chapter 33 Hybrid Drive Systems Diagnosis and Repair 651
Copyright by Goodheart-Willcox Co., Inc.
To check the power cables, note the conductor resis-
tance values of the high-voltage circuit in the data list
display of your scan tool. If these values are not within
specifi cations, tighten or repair the cable ends or replace
the hybrid power cables, if needed.
If your scan tool reading shows a ground fault problem
with the cables, they may be leaking current to frame or body
ground. Touch your ohmmeter test lead on one end of the cable
terminal and connect the other meter lead to frame or body
ground. If the ohmmeter reading is lower than specs (usually
around 350 k ohms), the insulation may be leaking high voltage
to ground and the cable should be replaced. See Figure 33-10.
Note: A high-voltage fuse will open and
disconnect the battery pack power if current
fl ow becomes too high due to a short. If this
happens and no power is reaching the electric drive
system, fi nd out why the fuse burned open. Correct
the problem. Then, install a new high-voltage fuse.
A loose cable end can overheat and burn the electri-
cal connection. Always torque the hybrid cable fasteners to
factory specifi cations using a torque wrench to ensure the
connection is not too loose or too tight.
To replace a high-voltage power cable, disconnect
both ends of the cable. Remove the clips that secure the
power cable to the vehicle. Finally, install the new power
cable in reverse order of removal.
Power Control Module Service
As discussed in Chapter 22, the hybrid power control
module contains several circuits or modules that convert
AC to DC and DC to AC. They also step voltage up or down
using transformers. A trouble code will normally be set
when problems develop in the power control module.
Sometimes a circuit board in the power control mod-
ule can fail and require replacement. A lack of normal air
or coolant fl ow can cause power control module overheat-
ing, which will set trouble codes.
Some hybrid vehicles use discrete (separate) invert-
ers. For example, Figure 33-11 shows a DC-to-DC inverter
Figure 33-10. By connecting an ohmmeter between each drive
cable end and ground, you can fi nd any cable that is leaking
voltage. The cable’s insulation may have broken down, allowing
small amounts of current to leak out of the circuit. (Toyota)
KΩ
Figure 33-11. This DC-to-DC inverter is a discrete unit. It mounts in engine compartment on the fi rewall of the vehicle. (Ford)
Low-Voltage
Battery Cable Nuts
DC/DC
Converter
Electrical
Connector
DC/DC Converter
Assembly