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Testing Codes & Understanding the ALDL Connector

Terminal IdentificationA = Ground
B = Code Test
D = Check Engine Light
F = Automatic TCC
G = Fuel Pump Test

These terminals are used to test for engine trouble codes, fuel pump operations, engine light functionality and automatic TCC operation

Testing for Engine Trouble CodesWith the ignition "off", insert a jumper wire between the A & B terminals. Turn the ignition to the "run" position but do not start the car. The check engine light will start a sequence of blinks.
For example: 1 flash, pause, 2 flashes
This sequence would denote code 12 which should be present every time you test for codes. Any stored trouble codes will follow code 12.
View the ECM Trouble Codes link in the Tech section for a full list of codes and their possible causes.

Test the Automatic TCC CircuitTerminal F is used to test the TCC circuit in the automatic transmission.
Fuel Pump TestTerminal G is used to test the operation of the fuel pump without removing the tank or unplugging the relay.
Apply 12 volts directly to terminal G and the fuel pump should run. This makes it easier to see if a pump is functional and provides the correct amount of fuel pressure. This can also be helpful when trying to drain old fuel. You can disconnect the fuel feed line, run it into a suitable container and activate the pump in order to completely drain the tank & lines.