System Diagnosis: Notes

WARNING: This page is about a different car, the 1991 Mitsubishi 3000GT. However, it is still accessible from the selected car via links, so may be relevant.

Engine Control Unit (ECU) monitors several different engine control system circuits. If an abnormal input signal occurs, a fault code is stored in ECU memory and given 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 critical fault code is set, ECU will turn on CHECK ENGINE light. All fault codes except speed sensor are considered critical.

Fault codes can be confirmed by using a voltmeter. See ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) in this article.

System malfunctions encountered are identified as either hard failures or intermittent failures as determined by ECU.