Actron GM Code Scanner CP9001 - Manual (Page 26)

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Diagnostic Mode.” The flashing
“Check Engine” light shows how the
fuel control system is operating.
See below.
Read Section 7, “Computer Basics”
or Section 8, “Glossary” for an
explanation of Open Loop and
Closed Loop operation.
IMPORTANT: The oxygen sensor
needs to be hot so the computer
can check the signal for proper fuel
delivery. Warm the engine by idling
for 2 minutes at 2000 RPM. Then,
gently rev the engine from idle to
part throttle several times. (This
creates a changing sensor signal
for the computer.) Finally, keep the
throttle steady, or at idle, for the rest
of the test.
Light flashes
2 times a second
The computer is in
Open Loop
operation. The
computer will run
“open loop” if it does
not see an oxygen sensor signal
because...
– The oxygen sensor is not hot
enough to operate (normal
condition if engine too cold or
sensor cooled down during idle)
or,
– Open circuit problems exist (bad
sensor or wiring). Note that this
condition will generate a trouble
code.
Light flashes
once a second
The computer is in
Closed Loop
operation. The
oxygen sensor is
sending a signal.
• Light equally ON and OFF while
flashing: system is running
correctly (proper air/fuel mixture).
• Light mostly ON while flashing:
system is running “rich”.
• Light mostly OFF while flashing:
system is running “lean”.
Various mechanical, electronic or
wiring problems can cause the
computer to sense a “rich” or “lean”
running engine. Usually these
conditions will generate a trouble code,
such as 44 (lean exhaust) or 45 (rich
exhaust). Follow vehicle service
manual troubleshooting charts to find
the cause. The Field Service Test lets
you check to see if the problem was
fixed. (Light flashing equally ON and
OFF once a second.)
Note: While in the “Field Service
Mode”...
– New trouble codes are not stored
in computer memory.
– On some engines, the computer
will send a signal for a fixed spark
advance.
5) Turn Ignition Key OFF
• Remove
Code
Scanner
and re-
install
connector
cover, if
supplied.
• The
computer
system is
now back
to normal.
• This completes the Field Service
Test.
TM
GM 1982 & higher - CP 9001
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