This evening, I was running the OBD-2 software, watching a replay of my drive home, with both of the O2 sensors being graphed. Most of the time, both O2 sensors seem to show normal activity, with sensor 1 showing, perhaps, a lower voltage level than usual. From time to time, however, both sensors, in unison, would drop to zero and stay there for a short while, before resuming normal activity. When this happens, the SYS STAT item on the DATA display switches from the normal closed loop mode to ?Open loop due to detected system fault?, returning to closed loop shortly after the O2 sensors resume normal behavior. On this particular journey, I only got one PTC, which was P1131. It occurred right after one of these instances where the two O2 sensors dropped to zero. Apparently, the PCM doesn't see a need to generate a trouble code every time this occurs.
I wonder if I'm looking at something as simple as a loose or dirty conenctor somewhere. Is it possible that there is, at some point, a single connector, where both O2 sensors are grounded through a common pin?
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Moonlight Blue 1996 Mercury Mystique GS , Zetec engine, ATX. No mods. (Well, OK, one mod. Before I got rid of my previous car, a 1994 Tempo, I swapped radios. I liked the Tempo's radio better. That counts as a mod, doesn't it? I also kept one of my Tempo's wheels to use as a spare. I hate those stupid ?compact? spares that come with modern cars. Does this count as a mod? If so, I guess I have two mods. Replaced burned/melted blower switch and connector on 19 February 2002 with a 1P3T toggle switch from Marvac and a Molex connector from Rat Shack; I guess this now makes three mods.)
