Diagnostic Circuit Check
The Diagnostic Circuit Check is an organized approach for identifying fuel injection problems using the Assembly Line Data Link (ALDL). This communication link can provide diagnostic information for display on any "Scan" tester designed for this purpose.
If the "Scan" tester is not operating, check tester on another vehicle. If okay, the cigar lighter socket should be checked for 12 volts and a good ground. With the ignition on, if the "Scan" tester reads "NO DATA" or "NO ALDL", check the serial data wire for an open or short to ground. Also check for an open diagnostic "test" terminal "B". Refer to appropriate CHART A1 schematic for circuit wiring reference. With the ignition on, the serial data line should vary between 2-5 volts and the diagnostic line should have about 5 volts present. See SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS table in this article.