"Scan" Diagnostic Circuit Check
The "SCAN" Diagnostic Circuit Check is an organized approach for identifying fuel injection problems using an assembly line communication link (ALCL). 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 ALCL", check the serial data wire for an open or short to ground between ALCL terminal "E" and the ECM. Also check for an open diagnostic test terminal from ALCL terminal "B" and ECM. With ignition on, the serial data line should vary between 2-5 volts and the diagnostic line should have about 5 volts. See SCAN TESTER USAGE and SCAN TESTER - TEST DATA PARAMETERS in this article.