Diagnostic Circuit Check: Notes

The diagnostic circuit check is an organized approach for identifying fuel injection problems created by an electronic engine control malfunction. The Assembly Line Data Link (ALDL) can provide diagnostic information for display on a "Scan" tester or any tester designed for this purpose. If a stored code is displayed, code definitions will aid in determining if fault is still present (hard failure) or result of an intermittent condition not normally diagnosed using code charts. Data parameters shown on tester can be compared to a similar vehicle or typical values shown in SCAN TESTER - TEST DATA PARAMETERS table in this article.

If "Scan" tester is not operating, check on another vehicle. If okay, the cigar lighter socket should be checked for 12 volts and a good ground. Also check for an open ALDL "test" terminal between ALDL terminal "B" and ECM. With ignition on, diagnostic line (ALDL terminal "B") should have about 5 volts present.