The ECM is a computer that can sense faults in the electronic engine control and store this fault information in its memory. This troubleshooting sequence describes how to get fault information from the ECM with a key in the ALDL and read the fault code from the Service Engine Soon light.
*****A dummy connector can be used to short terminals A and B in the diagnostic connector. *** If Terminal B is connected to Terminal A when the ignition switch is ON and the engine is stopped, all faults are indicated by a code (a sequence of illuminations) from the Service Engine Soon light.****
When the ignition switch is ON and the engine is stopped, the Service Engine Soon light will illuminate in a sequence to indicate a Code 12. A Code 12 is indicated by one long flash of light followed by a pause and then two short flashes to indicate that the fault monitor system is operating. A Code 12 only indicates that the fault monitor system is operating. The fault monitor system will repeat a Code 12 twice more and then send another code sequence if there is a fault. If there are no other fault codes stored in the ECM, a series of three Code 12 sequences continue to repeat as long as the SCAN Tool Tester or the dummy connector is plugged into the diagnostic connector and the ignition switch is turned to ON.
The code sequence occurs slowly at a rate of approximately one flash per second. Service people must wait long enough to make sure they have the complete and correct code sequences before beginning troubleshooting.

4-pin diagnostic connector.
Connect terminal A-B
check mail
SCAN Tool
Reads problem codes from the ECM memory. Used to
analyze and troubleshoot components and the ECM
operation of the electronic engine control system.
SCAN Tool will also record data stream information
when the engine is operating. This procedure will
record information that is not regular nor constant
or that only occurs during some conditions.
Available from:
Rinda Technologies Inc.
4563 North Elston Ave.
Chicago, IL 60630
part no 95050H
adapter 94005H

No I didn't. I don't have a scan tool. I'm looking for one. Or a way to flash the codes on the control panel. Like the old Chevys use to.

Did you get my message?
When the SCAN Tool is connected to the Diagnostic
Connector with the key switch ON and the engine
OFF, the system will enter the Diagnostic Mode.
1. Display a DTC 12 by flashing the Malfunction Indicator
Lamp (indicating the system is operating
correctly).
2. Display any additional stored DTCs by flashing
the Malfunction Indicator lamp. Each DTC will
flash 3 times, then DTC 12 will flash again.
3. The Idle Air Control (IAC) valvemoves to its fully
extended position, blocking the idle air passage.
Field Service Mode
NOTE: The ignition timing can be set with a timing
light.
If the SCAN Tool is connected to the Diagnostic Connector
and turned ON with the engine running, system
will enter Field Service Mode. For the GM 3.0L
engine, this will cause the engine to run at approximately
1500 rpm and 8 before top dead center spark
advance. For GM 4.3L engine, the numbers are approximately
1000 rpm and 0 before top dead center
spark advance. While the system is in Field Service
Mode, new trouble codes can be kept in the ECM.
ECM Learning Ability
The ECM has a learning ability that lets it make corrections
for variations in the idle system to improve
idle performance. If the battery is disconnected for
any reason, the learning process resets and begins
again. To teach the vehicle, make sure that the engine
is at operating temperature. Drive the lift truck
at part throttle, with moderate acceleration, and idle
until normal performance returns.

I have disconnected the battery. The light comes back on after awhile. Yes the year is a 2000. Serial number is K005D02125X. Thanks

Is the year of the truck a 2000? a serial number or atleast the series part of the serial number would be a good help to be sure you get correct information.
There are not likely to be any codes until models made AFTER 2002/2003.

to clear the codes disconnect the battery for 15sec. with square connector(latter model) connect A and D