OBD-II HEGO Identification & Location
Earlier systems (pre-'96) used only 1 HEGO immediately before the first cat.
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Before madly ripping out all the emissions systems on your vehicle, read
this article.
Upper pane is for 4 HEGO systems (OBD-II). Middle pane is for 1 (EEC-IV) or 2 (inline engine OBD-II). Rare 3-HEGO system (not shown) for early OBD-II uses locations 11, 21, & 12 (single downstream at catalyst exit). Lower pane is Catalyst Monitoring Function.
'96 Bronco HEGO12 is at the outlet of the 2nd cat, just before the pipe hanger & flange for the muffler inlet.
My '93 5.8L uses Bosch HEGO F1UF-9F472-AA (DY-731), 0 258 003 384, 366 16 90, 3 F 16 (probably the date code: 1993 6th month 16th day).
