System Diagnosis: Notes

System diagnosis can be accomplished using an appropriate scan tester, a voltmeter or the Malfunction Indicator Light (MIL). See RETRIEVING CODES  . Engine Control Module (ECM) monitors several different engine control system circuits. If an abnormal input signal occurs, a trouble code is stored in ECM memory and assigned a trouble code number. Each circuit has its own trouble code number and message. A specific trouble code indicates a particular system failure, but does not indicate that cause of failure is necessarily within system.

A trouble code does not condemn any specific component; it simply points out a probable malfunctioning area. If a trouble code is set, ECM will turn on MIL. System malfunctions encountered are identified as either hard failures or intermittent failures as determined by ECM.