How To Diagnose The System

WARNING: This page is about a different car, the 1988 Cadillac Allante and 1987 Cadillac Allante. However, it is still accessible from the selected car via links, so may be relevant.

This should be the starting point for any diagnosis of any customer complaint which does not directly relate to a specific subsystem, or to obtain a detailed understanding of the vehicle self-diagnostic capability.

Is the "Engine Control System Fault" Light Working?

If this telltale light fails to illuminate during cranking, then the problem could be in the power supply circuits to the computer system. The Self-Diagnostic Check will direct you to an appropriate diagnostic flow chart. See SELF DIAGNOSTICS SYSTEM CHECK in the SELF-DIAGNOSTIC article unde ENGINE PERFORMANCE.

Can Service Mode Be Accessed?

If the display is not operating, self-diagnostics cannot be used. In this case the Self-Diagnostic System Check will lead you to an appropriate diagnostic flow chart.

Is There A Trouble Code Stored?

If a trouble code is identified by performing the self-diagnostics, a problem can be detected by the system which can be corrected using the diagnostic flow chart.Codes with an "E" prefix are ECM codes. Codes with a "B" prefix are BCM codes. Codes with an "L" prefix relate to the distributed lighting system. If no faults are detected, the Self-Diagnostic System Check will direct you the appropriate diagnostic procedure.