ECM Trouble Codes: Notes

1. The ECM receives signals from sensors concerning engine operating conditions. If the sensor reading is not what it should be, the ECM will turn on the "CHECK ENGINE" light on the instrument panel, and will store a trouble code in the memory.
2. To obtain a stored trouble code from the ECM, the assembly line communication link (ALCL) is used. ALCL is located in passenger compartment. To enter the diagnostic mode, connect test terminal (terminal B) to terminal A or ground with the engine stopped. See Fig 1 .
   Fig 1: ALCL Connector

   
3. The ECM will first display a code "12" to indicate the system is operating. Code are displayed by flashing the "CHECK ENGINE" light. Code 12 consists of a flash, followed by a short pause, then 2 quick flashes in succession.
4. Other codes are displayed in a similar manner. Each code will be displayed 3 times. Codes can be cleared from the ECU memory by disconnecting the ECU harness from positive battery pigtail for 10 seconds with ignition off. The following codes indicate these problems: