Self-Diagnostic System: Notes

ECM constantly looks at information from various input devices to control systems that affect vehicle performance. ECM self-diagnostic capabilities allow for trouble shooting system through a CHECK ENGINE light. CHECK ENGINE light will illuminate to alert driver of a system malfunction. The type of failure (hard or intermittent) will affect how the CHECK ENGINE light illuminates. The specific malfunction can be determined via a 2-digit code displayed by CHECK ENGINE light. To retrieve codes, see G - TEST W/CODES article.