System Diagnosis: Notes

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

A fault code does not condemn any specific component; it simply points out a probable malfunctioning area. If a fault code is set, ECM will turn on Malfunction Indicator Light (MIL). Fault codes can be confirmed by using a voltmeter. System malfunctions encountered are identified as either hard failures or intermittent failures as determined by ECM.