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TOYOTA TECHNICAL
This meter is connected
to measure
battery voltage.
Flash calibration updates for
specifi c vehicle models/ECUs are
released as fi eld-fi x procedures
described in individual service
bulletins.
Flash reprogramming can
be accomplished by using the
Techstream unit. It is vital to understand
that maintaining proper
voltage level of the battery during
fl ash reprogramming is critical to
avoid ECU damage and programming
errors. During fl ash reprogramming,
battery voltage must
not fall below 11.4V, and must not
rise above 16.0V. The target voltage
is 13.5V.
The GR8 Battery Diagnostic
Voltage drop indicates the voltage being used in
that section of the circuit.
Station must be used in its “Power
Supply Mode” to hold the battery
at 13.5V during reprogramming.
UNDERSTANDING AND
READING VOLTAGE DROP
Voltage drop is a factor to consider
when concerned with maintaining
battery voltage during
diagnosis, fl ash reprogramming,
etc., whenever voltage passes
through any component, voltage
is “consumed,” or used up. The
amount of voltage that is used up
is referred to as voltage drop.
The voltage drop of a component
is directly proportional to
the resistance of the component.
The greater the resistance, the
greater the voltage drop.
Low resistance components
such as fuses, switches, wires
and connectors should have a
very low voltage drop.
As a general rule, the
maximum allowable
voltage drop for these
components is less than
0.1V per component or
connector.
Higher resistance components
are usually referred to as loads.
Loads use their resistance to convert
current into work (light, heat,
motion).
This conversion causes a voltage
drop as the electrical pressure
is used up. Typical loads include
lamps, motors, relay coils and
most sensors.
In any electrical circuit, all of
the voltage will always be used
up. Adding up all of the voltage
drops in a circuit will always equal
source voltage.
Voltage drop tests can isolate
unwanted high resistance in the
charging system. High resistance
can cause problems such as:
• Charging system cannot fully
charge the battery.
• Abnormally high current is
Voltage drop tests can isolate high resistance
in the charging system. Test voltage
drop on the positive and the ground side of
the battery.
8 STAR Service News
Spring 2010