- Powertrain/On-Board Diagnostic System Check

The "Self-Diagnostic System Check" is an organized approach for identifying a problem caused by the on-board computer controlled electronics. Understanding this chart and using it correctly will reduce diagnosis time and prevent the unnecessary replacement of parts.

Notes on trouble trees
1. This process assures that there are no BCM inputs active that would not allow the system to "WAKE-UP" in the correct sequence. Are the Instrument Panel Cluster (IPC) and COMBO Panel displays operating? If these displays are not operating, then the problem is related to Power and Ground circuits to the IPC, COMBO PANEL, OR BCM.
2. Is the "Engine Control System Fault" Telltale working? If this telltale fails to illuminate during crank, then the problem could be in the Power Supply Circuits to the computer system.
3. The odometer displays and "Engine Control System Fault" lamp work. Enter diagnostics and continue with code diagnosis chart. If diagnostics cannot be entered, refer to CHART C-1. Chart C-1 Vehicle Will Not Enter Diagnostics
Is there a trouble code displayed? If a trouble code is identified using the self-diagnostics, a problem has been detected by the system which can be corrected following the appropriately numbered code chart. Codes with a prefix of "E" are ECM Codes. Testing and Inspection
Codes with a prefix of "B" are BCM Codes. Body Control Module
Codes with an "L" prefix relate to the Distributed Lighting System. Lighting and Horns