Actron 9640A manual Code Lookup, Print Data, Code 12 will look like, Code 23 will look like

GM Historic (OBD I) Diagnostics

—DTC 12 (No RPM reference pulse) should display first since the engine is not running. If not, problems exist in the PCM or Check Engine light circuitry.

Code 12 will look like:

FLASH-pause-FLASH-FLASH — long pause.

Code 23 will look like:

FLASH-FLASH-pause-FLASH-FLASH-FLASH — long pause.

4)When Field Service Mode is ON, most computer controlled Relays and Solenoids will be turned ON, except for the fuel pump relay and fuel injec- tors. Toggle the Field Service Mode On and Off.

❒Use a voltmeter to measure Relays and Solenoids input voltage to verify On/Off conditions. An ohmmeter could be used to check the continuity between the relay’s switch terminals.

❒The Idle Air Control (IAC) valve is fully seated to the zero position by the PCM.

❒The Exhaust Gas Recirculation (EGR) solenoid is energized for 25 seconds.

KOER Procedure

With the engine running, theFieldService mode can be used to measure base timing, check open loop/closed loop operation, and determine if the engine is running rich or lean.

	1) Engage parking brake and block drive wheels.
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	2)	Verify engine is cold. If engine is hot or warm, allow it to cool.
	3)	On scan tool, place Field Service On.
	4) Start engine and place transmission in Park or Neutral. The Check Engine
		light will flash once.
	5)	Warm the engine by idling for 2 minutes at 2000 RPM.
	6)	Observe Check Engine light.
		• If Check Engine light flashes 2.5 times a second, the on-board
		computer is operating in Open Loop.
		• When the engine warms up to normal operating temperature, the
		on-board computer is now operating in Closed Loop. The Check
		Engine light should flash once a second. The on-board computer
		is now operating in Closed Loop.

• If Check Engine light...

— flashes equally ON/OFF, then the fuel system is running normally.

— is mostly ON, then the fuel system is running Rich.

— is mostly OFF, then the fuel system is running Lean.

7) On some engines, the spark advance timing is fixed during Field Service Mode. This allows the technician to measure the engine base timing.

Code Lookup

Refer to “Code Lookup” on page 4-14 of Global OBD II Diagnostics.

✓Enter only the code numbers. No system designation is used for historic DTCs, they are either History or Current codes.

✓A “P” appears at the beginning of the DTC if the vehicle uses OBD II type codes.

Print Data

Refer to “Print Data” on page 4-12 of Global OBD II Diagnostics.

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