My opinion: This is an opinions thread, not a "help me fix my car" thread.

Some facts (in my opinion :)

OBD is specified by the gubbmint, in both I and II versions. It is there to keep the air clean, not to diagnose driveability, nor to point knuckle-draggers to the part needing to be swapped. You think LH2.4 ECUs aren't smart enough to know whether they are "rich or lean at part load?" Sure they are, but OBD-I only required the out-of-range mixture event to be reported. For oldduke's slant (six I believe) the ignition switch operated OBD-I in mopar yields the same vaguely useful info for those years, if I remember correctly.

OBD-II is extended in different ways by manufacturers at their pleasure to help their dealer techs develop an "if this, then replace that" knowledge base, but the scam there is keeping that knowledge base proprietary to make it profit. Read the bimmer boards. But the baseline government requirement does not care whether the diagnostic facility can identify which oxygen sensor is reading what when. Just that the car is probably polluting the air.

The result of smarter control electronics seems to have the opposite effect on dealer/factory training. I suppose recently trained automotive techs could have trouble doing their day to day diagnostics without a symptom-cause map. I think this automation leads them to quickly lose the understanding of basic automotive theory that began their schooling.


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Art Benstein near Baltimore

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