GM Code Retrieval
Entering Diagnostic Mode
Turn ignition switch on but do not start engine, "CHECK ENGINE
" should glow. Locate test connector to ECM under instrument panel near
steering column. Insert jumper across "TEST" and
"GROUND" terminals.

"CHECK ENGINE" Light should flash Code 12. (Flash, Pause, Flash
Flash.) Code 12 will be repeated two more times. If any trouble codes are
stored they will be displayed in the same manner.
Trouble codes will be displayed from the lowest to the highest numbered
codes. (Three times each) and will be repeated as long as test terminal is
grounded.
To exit diagnostic mode, turn ignition switch off and remove jumper.
Reading Trouble Codes
The ECM stores component failure information for the CCC system under a
related trouble code which can be recalled for diagnosis and repair.
When recalled, these codes will be displayed by flashes of the Check
Engine Light. Trouble codes are read by counting the flashes of the CEL. For
example; Flash, Pause, Flash, Flash longer pause identifies as 12.

Clearing Trouble Codes
Trouble codes are cleared by removing battery voltage from the ECM for at
least 10 seconds. To do so, be sure ignition switch is in the OFF position
and remove the positive battery cable, or disconnect the ECM positive
pigtail from the battery, or remove the ECM fuse from fuse panel.
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