Actron GM Code Scanner CP9001 - Manual (Page 7)

7
When to Read Codes
Use the Code Scanner to read computer
trouble codes if...
“Check Engine” Light: Problem
Spotted!
Light ON and stays ON (when the
engine is RUNNING)
– The computer sees a problem that
does not go away. (A “hard” failure.)
– The light will stay on as long as the
problem is present.
– A trouble code is stored in computer
memory. (A “hard” code.)
– Use the Code Scanner at the earliest
convenient time to obtain codes.
Refer to section 3, “Reading Codes”.
“Check Engine” Light: Intermittent
Problem!
Light ON and then goes OFF (when
the engine is RUNNING)
– The computer saw a problem, but
the problem went away. (An
“intermittent” failure.)
– A trouble code is stored in computer
memory. (An “intermittent” code.)
– The light went out because the
problem went away, but the code
stays in memory.
– Use the Code Scanner at the
earliest convenient time to obtain
codes. Refer to Section 3, “Reading
Codes”.
NOTE: The computer will automati-
cally erase codes after several restarts
(typically 50) if the problem does not
return.
A Poorly Running Engine (No
“Check Engine” light)
Most likely this condition is not due to
computer system failures - but reading
codes can still be useful as part of a
basic troubleshooting procedure.
Review Section 4, “Using Codes”
before proceeding to Section 3,
“Reading Codes”.
• The “Check Engine” light comes ON
when the engine is RUNNING
or,
• Vehicle engine is running poorly and
“Check Engine” light is OFF.
The “Check Engine” light
The engine computer turns the “Check
Engine” light on and off as needed.
This dashboard message light is either
amber or red and labeled:
– “Check Engine” or,
– “Service Engine Soon” or,
– “Service Engine Now” or,
– marked with a small engine picture.
“Check Engine” light: Normal
Operation
The “Check Engine” light is normally
OFF when the engine is RUNNING.
NOTE: The light will come on when
ignition key is in ON position, but the
engine is OFF. (For example, before
you start the engine.) This is a normal
test of all the dashboard message
lights.
If the “Check Engine” light does not
come on, you have an electrical
problem which needs repair. Refer to
the “Diagnostic Circuit Check” steps in
the “Basic Diagnostic Procedures”
section of your vehicle service manual.
(Manual sources listed on page 4.)