On-Board Diagnostic System

PURPOSE

To aid in technical troubleshooting of the Programmed Fuel Injection (PGM-FI) System.

OPERATION
The Engine Control Module (ECM) monitors the output values of various sensors and compares them to an expected set of values. If the output values are outside of the given acceptable range (or not present) the ECM retains a record in memory. In the case of most sensors, a second occurence of the same sensor sending an out-of-range value must be noted before the ECM stores an output code and turns on the Malfunction Indicator Lamp (MIL). This "two-trip detection" is used to prevent false output of trouble shooting Diagnostic Trouble Codes (DTC) which would lead to unnecessary diagnostic procedures.