With Scan Tool

When trying to verify a speed control system electronic malfunction, one of two methods may be used and are described as follows:

If a DRB II Diagnostic Tool is available, plug tool into diagnostic connector and verify that either a fault (trouble) codes 15 or 34 on except 1991 Dodge Monaco & Eagle Premier is indicated or fault (trouble) codes 15, 34 or 77 on 1991 Dodge Monaco & Eagle Premier is indicated, then refer to the appropriate diagnostic chart, refer to DIAGNOSTIC CHARTS. Follow tool manufacturers instructions for proper installation of the tool prior to testing speed control system.
If no problems were found, replace engine controller.