General Information

Assembly Line Diagnostic Connector (ALDL).:

Scan Tool Hookup To ALDL Connector.:

PURPOSE
The provision for communicating with the PCM is the assembly line diagnostic link (ALDL) connector. It is located under the instrument panel. It is used in the assembly plant to receive information in checking that the engine is operating properly before it leaves the plant.


ACCESSING CODES
The code(s) stored in the PCM's memory can be read either through a hand held diagnostic scanner plugged in the ALDL connector or by counting the number of flashes of the "SERVICE ENGINE SOON" telltale lamp when the diagnostic terminal of the ALDL connector is grounded. The ALDL connector terminal "B" (diagnostic terminal) is the second terminal from the right of the ALDL connector's top row. The terminal is most easily grounded by connecting it to terminal "A" (internal PCM ground), the terminal to the right of terminal "B" on the top row of the ALDL connector.

Once terminals "A" and "B" have been connected, the ignition switch must be moved to the "ON" position, with the engine not running. At this point, the "SERVICE ENGINE SOON" telltale lamp should flash code 12 three times consecutively. This would be the following flash sequence: Flash, pause, flash-flash, long pause, flash, pause, flash-flash, long pause, flash, pause, flash-flash. Code 12 indicates that the PCM's diagnostic system is operating. If code 12 is not indicated, a problem is present within the diagnostic system itself.



READING PCM/EC (ENGINE) CODES
Following the output of code 12, the "SERVICE ENGINE SOON" telltale lamp will indicate a diagnostic trouble code three times if a code is present, or it will simply continue to output code 12. If more than one diagnostic trouble code has been stored in the PCM's memory, the codes will be displayed from the lowest to the highest, with the exception of code 11 which indicates transaxle codes.
Code 11 will always flash last followed by the "SHIFT TO D2" telltale lamp (or "HOT" lamp on 93-94 models) which will flash transaxle codes. Each code will be displayed three times.

For PCM/EC trouble codes and PCM/EC information flags, go to Diagnostic Charts in the section for "Computers and Control Systems". Testing and Inspection


READING PCM/TC (TRANSMISSION) CODES
Following the output of code 12, and PCM/EC (Engine) codes (if any), the "SERVICE ENGINE SOON" telltale lamp will output code 11 which indicates transaxle codes. Code 11 will always flash last followed by the "SHIFT TO D2" telltale lamp (or "HOT" lamp on 93-94 models) which will flash transaxle codes. Each code will be displayed three times.
Automatic transaxle diagnostic codes will not be flashed on the "SERVICE ENGINE SOON" light.


INFORMATION FLAGS
SATURN also uses information flags. These flags do not indicate a failure and will not turn "ON" the "SERVICE ENGINE SOON" telltale lamp. Information flags are used as diagnostic aids to the technician when hard codes or intermittent problems occur.

Engine information flags will not be flashed on the "SERVICE ENGINE SOON" telltale lamp and they can only be read with a Scan tool, but automatic transaxle flags will flash on the "SHIFT TO D2" telltale lamp.

Information flags for engine control system are listed under Diagnostic charts along with trouble codes, either in "Computers and Control Systems" or "Transmission Control Systems" depending on the flag.