Reading and Clearing Diagnostic Trouble Codes

The trouble code ``Test'' lead is located in a 12 volt terminal connector under the dash. When this terminal is grounded, the ECM will flash any trouble codes stored in the memory. To ground the terminal, connect a jumper wire between the ``Test'' lead terminal and the adjacent ground terminal.
If the ``Test'' terminal is grounded with ignition on and engine not running, the system will enter the diagnostic mode. In the diagnostic mode, the ECM will flash a Code 12 and energize all ECM controlled relays.
If the ``Test'' terminal is grounded with the engine running, the system will enter the field service mode. In this mode, the ``Check Engine'' light will indicate whether the system is in open or closed loop operation. If the light flashes approximately twice per second, the system is in open loop operation. Closed loop operation is indicated by the light flashing approximately once per second.