1) Technician Not Familiar With Self-Test Code Output

There are two types of EEC Self-Tests, Key On Engine Off (KOEO) and Key On Engine Running (KOER). While both of these will test for various "hard faults" that are present when the test is run, the processor continuously monitors various operating parameters whenever the engine is running. If the processor detects a problem, it will store a "Continuous Memory" code and light the MIL. These Continuous Memory codes are put out during KOE0 Self-Test after any codes associated with hard faults are output.

Self-Test Codes are displayed by flashing the MIL. They are also output as voltage pulses on the Self-Test Output (STO) circuit in the Self-Test connector. In either Self-Test mode, all codes are output twice and in KOEO, the hard fault codes are separated from the Continuous Memory codes by a "separator" pulse.

A technician that is unfamiliar with the EEC Self-Test can mistakenly believe that continuous Memory codes are not present when they really are. He may run KOER Self-Test and get a pass code (III) and not realize that KOEO Self-Test must be run to receive any Continuous Memory codes. He may run KOEO Self-Test while counting MIL flashes and misinterpret the repeated hard fault pass code (III) to mean that Continuous Memory does not contain any codes.