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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."
58
5) Turn the Diagnosis
Mode Selector fully
CLOCKWISE.
6) Have your pencil and
paper ready.
7) Observe the RED and GREEN
LED's.
• On the 300ZX Turbo only, codes 23,
24, and 31 should be displayed.
• Note any codes other than 23, 24,
and 31.
• On all other models codes 23, and
31 should be displayed.
• Note any codes other than 23, and
31.
8) Depress and
release
accelerator
pedal.
9) Observe the
RED and GREEN LED's.
• On the 300ZX Turbo only, codes 24,
and 31 should be displayed.
• Note any codes other than 24, and
31.
• On all other models code 31 should
be displayed.
• Note any codes other than 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.
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