STAR Service News Missed an issue? - Toyota Parts & Service

TOYOTA TECHNICAL
voltage drop reading (do not
crank the engine for more than 10
seconds at a time). 0.2V or less is
acceptable resistance. More than
0.2V is excessive resistance. If excessive
resistance is found, isolate
the cause, repair the fault and
re-test the voltage drop. Excessive
resistance in this case could
be caused by a damaged battery
cable, poor connection at the
battery and/or starter terminal
or poor connection between the
starter case and the engine block.
MAGNETIC SWITCH
This test measures the voltage
drop across the starter’s magnetic
switch. (NOTE: Starters with
planetary gear reduction do not
feature a magnetic switch).
Connect the meter’s red lead
to starter terminal C and connect
the meter’s black lead to starter
terminal 30. Crank the engine and
note the voltage drop (again, do
not crank the engine for more
than 10 seconds at a time). 0.3V or
less is acceptable resistance. More
than 0.3V indicates excessive
resistance. If resistance is excessive,
isolate the cause, repair and
re-test. NOTE: A faulty magnetic
switch could cause excessive
resistance.
STARTER CONTROL
CIRCUIT
Excessive resistance in the starter
control circuit can reduce the
voltage available to the magnetic
switch. Symptoms include nonengagement
of the pinion gear
and only partial gear engagement.
The areas where excessive
resistance can occur include the
ST contacts of the ignition switch,
neutral start switch/clutch start
switch and circuit wiring and connections.
Test for excessive resistance in
the starter control circuit. Connect
the meter’s red lead to the
positive (+) battery terminal and
connect the black lead to terminal
50 on the starter motor. On a vehicle
equipped with an automatic
transmission, put the shift selector
in Park or Neutral. If equipped
with a manual transmission,
depress the clutch pedal.
Crank the engine (do not
crank for more than 10 seconds
at a time) and note the voltage
drop. 1.2V or less is acceptable.
More than 1.2V is an indication
of excessive resistance. Measure
the voltage drop across the
ignition switch and the neutral
start/clutch switch.
0.1V or less is acceptable.
More than 0.1V
indicates excessive
resistance.
If excessive resistance
is found, isolate
the problem, repair
and re-test.
As you can see,
testing for voltage
drop can be a useful
diagnostic tool.
As mentioned earlier with
regard to fl ash reprogramming
an ECM, maintaining a steady
voltage is critical to avoid ECM
damage. An excessive voltage
drop can certainly contribute to
reprogramming errors and damage
to a control unit. This helps to
illustrate why use of the GR8 battery
station is so helpful, since it
maintains a constant 13.5V during
fl ash reprogramming.
CURRENT FLOW
Current is the term used to
describe the fl ow of electrons
through the circuit. It is this fl ow
of electrons that performs the
“work” in the circuit. The unit for
measuring the amount of current
fl ow is the ampere or amp (A).
One amp equals 6.28 billion billion
electrons per second fl owing
through a circuit.
Current will only fl ow if there
is a complete circuit (continuity)
between a source of higher voltage
(power) and a lower voltage
(ground). Voltage is the pressure
that pushes the electrons through
the circuit, and Amperes is a measure
of the number of electrons
fl owing through the circuit.
Measured in amps (A) or milliamps (mA), current
fl ow is caused when a voltage or pressure
differential exists at both ends of a conductor.
The combination of amperage
with voltage determines the
amount of power that is being
used at the load in the circuit.
Power is measured in watts (W).
The amount of power that is being
used by a load can be determined
by multiplying the amperage
through the load by the
voltage drop across the load. ★
12 STAR Service News
Spring 2010