Ignition Coil Switching Action - Bosch FIX 7677 Mode D'emploi

Ignition Coil Switching Action

This test checks to see if the negative
terminal of the primary ignition coil is
getting switched ON and OFF via the
ignition module and camshaft / crank-
shaft position sensors. This switching
action is where the RPM or tach signal
originates. This test is primarily used for
a no start condition.
Test Procedure (see Fig. 29):
Fig. 29
Typical
Ignition
Coil
Red
Black
Ground
1. Insert BLACK test lead into COM
test lead jack.
2. I n s e r t R E D t e s t l e a d i n t o
3. Connect RED test lead to TACH
signal wire.
• If vehicle is DIS (Distributorless
Ignition System), then connect RED
test lead to the TACH signal wire
going from the DIS module to the
vehicle engine computer. (refer to
test lead jack.
vehicle service manual for location
of this wire)
• For all vehicles with distributors,
connect RED test lead to negative
side of primary ignition coil. (refer
to vehicle service manual for loca-
tion of ignition coil)
4. Connect BLACK test lead to a
good vehicle ground.
5. T u r n m u l t i m e t e r r o t a r y
switch to correct CYLINDER
selection in RPM.
6. View reading on display while
engine is cranking.
• Typical cranking RPM range
is 50-275 RPM depending on
temperature, size of engine,
and battery condition.
• R e f e r t o v e h i c l e s e r v i c e
manual for specific vehicle
cranking RPM range.
7. Test Results.
Good Coil Switching Action: Display
reading indicated a value consistent
with manufacturers specifications.
Bad Coil Switching Action:
• Display read zero RPM, meaning
the ignition coil is not being
switched ON and OFF.
• Check ignition system for wiring
defects, and test the camshaft and
crankshaft sensors.
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