GM Storm/Spectrum 1985-1993 Repair Guide

Entering Self-Diagnosis


To enter the diagnostics, either connect a scan tool to the ALDL or use a jumper wire to connect terminals 1 and 3. Turn the ignition switch ON , then the ECM will enter the diagnostic program and report trouble Codes on the scan tool or by flashing the CHECK ENGINE light.

All Codes are 2 digits between 12 and 51. Codes are displayed on the CHECK ENGINE light by flashing the MIL with short and long pauses to distinguish digits of 1 code from digits of another. The short pause is used between digits of the same code, long pauses are between codes. For Code 12, the sequence will be: flash, pause, flash-flash, long pause.

  1. When the diagnostic mode is entered, Code 12 is displayed 3 or 4 times, depending on the vehicle. This indicates that the internal diagnostic system is operating. If Code 12 is not displayed, the self-diagnostic program is not functioning properly. If only Code 12 is displayed, no system malfunctions have been stored.
  3. After code 12 flashes to indicate diagnostic display, any existing system fault Codes are displayed in order from lowest to highest code number. Each Code is displayed 3 times, followed by the next Code, if any.
  5. When all engine and transaxle Codes have been displayed, Code 12 will flash again.