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Feedback System Check
- Turn diagnosis switch on, located under steering column, under left side of dash. See Fig 1
. Turn ignition on, but do not start engine. CHECK ENGINE light will begin to flash a code 12.
- Code 12 will flash 3 times and a trouble code will flash 3 times and continue to cycle in this sequence. See Fig 2
. A code 12 consists of one flash, a short pause and 2 flashes.
Courtesy of GENERAL MOTORS CORP.
Courtesy of GENERAL MOTORS CORP.
- Code 12 is a normal operation and means diagnosis system is functioning properly. After a code 12 flashes, any trouble codes stored in ECM memory will begin to flash.