From the Ford Manual:
Octane Adjust Shorting Bar
The Octane Adjust (OCT ADJ) shorting bar is used to retard spark timing. Removal of the shorting bar from the in-line connector will typically retard spark three degrees.
The purpose of the OCT ADJ self-test is to check the state of the OCT ADJ shorting bar. A Diagnostic Trouble Code (DTC) will be present if the shorting bar is removed or if there is an open circuit. The OCT ADJ shorting bar is similar in shape to the SPOUT in-line connector. On some applications the Power Steering Pressure (PSP) circuit will also have a similar shorting bar connector. DO NOT remove the shorting bar unless directed by a Technical Service Bulletin (TSB).
You may have an open that has developed in the circuit, or maybe the plug (short bar) has become loose.