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Chapter A: General Diagnosis

Cranking Current Draw Test

The cranking current draw test measures the amount of
current, in amperes, that the starter circuit requires to
crank the engine. This test, which helps isolate the
source of a starting problem, is performed with either a
charging-starter-battery (CSB) analyzer, or individual
voltmeter and inductive ammeter. To test with inductive
ammeter meter:

1. Bypass the ignition with a remote starter switch.
2. Connect the voltmeter leads to the battery termi-

nals observing correct polarity.

3. Clamp the inductive ammeter pickup around the

positive cable.

4. Crank the engine for several seconds and note the

voltmeter and ammeter readings, figure 1-32.

5. Compare ammeter readings to specifications.

With a CSB analyzer, connect the leads and test ac-
cording to the equipment instructions. Regardless of
method, high current draw is caused by a short in the
starter circuit or a binding starter motor or engine. Low
current draw results from high resistance in the starting
system circuit or an undercharged or defective battery.

High resistance in the cranking circuit can cause either
high or low current draw. This is because the starter
motor requires high current to get up to speed. Once up
to speed, the starter motor acts like a generator to pro-
duce a counter voltage which limits the current. Be-
cause the motor requires high current when turning
slowly, high resistance can prevent a starter from get-
ting enough current to get up to speed. As a result, the
motor turns slowly and does not limit the current.

If resistance is high enough, it limits current to the
starter, which causes the starter motor to turn slowly or
not at all. High resistance can be seen on the ammeter
when the starter is first engaged. If current momentari-
ly goes high, then settles down to a lower amount, sus-
pect high resistance.

When high resistance is indicated, perform starter cir-
cuit resistance. If testing indicates a starter motor prob-
lem, remove the unit for service.

Cranking Voltage Test

This test, which measures available voltage at the
starter during cranking, is performed to check for high
resistance in the starter circuit. Test results are read on
a voltmeter. To test:

1. Bypass the ignition switch with a remote starter

switch.

2. Connect the negative voltmeter lead to a good

ground and connect the positive voltmeter lead to
high current circuit to the starter. Some manufac-
turers recommend connecting the voltmeter di-
rectly to the starter, while others specify testing at
the relay or solenoid, figure 1-33. Check the Ser-
vice Manual for exact procedures and specifica-
tions.

3. Crank the engine while monitoring the voltmeter.

To interpret test results if the starter motor cranks poor-
ly, and if voltage is:

•9.6 or more and the amperage is high, the problem

is in the motor, ignition timing is too far advanced,
the engine is tight and binding, or there is high cir-
cuit resistance. The battery is good and the starter
motor is getting enough current to operate.

•9.6 or more and the amperage is low, the problem is

high resistance. The battery is good, but there is not
enough current through the starter motor.

• 9.6 or less and the amperage is high, the problem

is in the motor, ignition timing is too far advanced,
the engine is tight and binding, or there is high cir-
cuit resistance. The high amperage draw pulls down
the battery voltage and the battery may be faulty.

•9.6 or less and the amperage is low, the battery

should be tested.

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