Bob:
For a 96 Zetec, I would guess the car mileage is approaching 70K miles, more or less?
I think you had the answer right under your nose
too close for you to see?
Originally posted by Bob Blaylock:
... 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...
My guess is that given the mileage, the O2 sensor eventually got contaminated with lead, carbon, metals from motor oil additives, and silica (from high-volatile RTV silicone sealants or anti-freeze) in the exhaust. The contaminations would have coated the sensor's platinum, rendering it sluggish with time. (This said, a poor-man O2 sensor rebuilt can be achieved by removing these coatings by soaking the tip in solvent such as gasoline overnight, and blow dry it in the morning?? It is also assumed that gasoline as solvent does not also *remove* the thin precious platinum coating, that may be at the end of its life cycle after 70K miles!)
It is worth noted that the PTC was set during closed loop, the engine was warmed up and the sensor was heated, i.e. the sensor was up and running for a while. Then "from time to time"
both sensors dropped dead momentarily!? It may be coincidental and sensational that both need to be replaced, i.e. aged at the same rate, but when they're gone, they're gone
!
However, you can wait until the PTC becomes DTC, as you seem to have the tool to play with them for a little longer. It would be less of a game when it is over?
I found this link provides more info on the O2 sensor (not again
!)
Oxygen Sensor: Operation and Testing Dave
