2) Inadvertent Erasure of Continuous Memory Self-Test Codes

Continuous Memory Self-Test codes are erased by ungrounding STI before KOEO Self-Test is complete and all KOEO and Continuous Memory codes have been displayed. It is possible to inadvertently erase Continuous Memory codes by ungrounding STI without realizing that KOEO Self-Test is not complete or the processor has not finished displaying all the codes.

The EEC Self-Test codes are not only used by service technicians, they are used as a final system test in the assembly plants. To make this test as efficient as possible, Self-Teat codes are output as a very fast, short pulsewidth signal before the codes are displayed by the flashing MIL. These "FAST" codes can only be interpreted by end-of-line equipment or code-reading testers like Ford's Self-Test Automatic Readout (STAR) testers.

The EEC-IV processor puts out both 2-digit and 3-digit Self-Test codes in both formats, "FAST" pulsewidth mode and "SLOW" pulsewidth mode. While all "STAR" type testers display 2-digit codes, the original STAR tester cannot display 3-digit service codes. If the STAR tester is used on 3-digit service code applications, the display will be blank but the tester will beep. The beeps can be counted to determine service codes. The SUPER STAR tester will only display 3-digit service codes in "FAST" code mode. If slow code mode is used on 3-digit service code applications, the display will be blank but the tester will beep. The beeps can be counted to determine service codes. For more information on running Self-Test, refer to the "EEC-IV Quick Test Procedures and Appendix" section of the Powertrain Control/Emissions Diagnosis service manual.

Since certain STAR testers are capable of reading and displaying fast codes before the slow codes are finished being output on the MIL, a technician can assume that since he sees codes displayed, he can unground ST and move on. If he ungrounds STI before all slow codes are output, Continuous Memory will be erased and could put out a pass code (II/III) the next time KOEO Self-Test is run. The technician may also realize that his tester is in "SLOW" mode after he has initiated the KOEO test and stop the test to change tester settings. Another possibility is that another person, a vehicle owner or another technician, could have erased the codes before the technician reporting the situation has run Self-Test. In any of these situations, the vehicle must be driven until the Continuous Memory codes are reset.