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1) Mark the initial setting of the
Diagnostic Mode Selector
on the computer
housing.
IMPORTANT: The
Diagnostic Mode
Selector is a potentiom-
eter. It is critical that the
initial position (setting)
of this potentiometer be marked on the
computer housing so that when testing is
complete, it can be reset to its original
position!
2) Using the Selector
Tool or other means,
turn the Diagnosis
Mode Selector to the
fully COUNTER-
CLOCKWISE position.
3) Turn the
ignition
switch ON,
but do not
start the
engine.
4) Check to see that
both the RED and
GREEN LED's turn
ON and stay ON.
• If they do, proceed to the next step.
• If they do not, you have a problem
with the battery supply circuit which
feeds the computer (ECU), or the
ECU itself is defective. This failure
must be repaired before proceeding.
Refer to the vehicle service manual.
Some publications have this
information in books or sections
called "Computerized Engine
Controls", "Electronic Engine
Controls", or "Tune-Up Information."
56
5) Turn the Diagnosis
Mode Selector fully
CLOCKWISE.
6) Have your pencil and paper ready.
7) Observe the RED and GREEN
LED's.
• Codes 23, 24, (300ZX Turbo only)
and 31 (all vehicles) should be
displayed.
• Note any codes other than 23, 24,
and 31.
8) Depress and
release
accelerator
pedal.
9) Observe the RED and GREEN
LED's.
• Codes 24, (300ZX Turbo only) and
31 (all vehicles) should be
displayed.
• Note any codes other than 24, and
31.
10)(For 300ZX Turbo only. All others go
to Step 12). Move the gear shift
lever from Neutral to the highest
gear and
then back to
Neutral.
11)Observe the RED and GREEN
LED's.
• Code 31 should be displayed.
• Note any codes other than 31.
12)Start the vehicle's engine.
13)Observe the RED and GREEN LED's.
• Codes 14, (300ZX Turbo only) and
31 (all vehicles) should be displayed.
• Note any codes other than 14, and
31.
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