My problem is OBDII monitors of with a "Not Ready" Status for Oxygen Sensor, Oxygen Sensor Heater and Catalyst. Three other monitors , Misfire , Fuel Sys and Comp Cmpnt have a ready Status. No check engine light and No codes . I have checked the Oxygen sensors by back-probing .. 3 measured Ok and were switching 200mV <-> 900mv , the 4th read nothing but I suspect a probe connection problem. I disconnected the 4th sensor and got a check engine light after about 5 miles.

It is a long time since the battery was disconnected and the OBDII should have trained by now.

The only thing I don't see that the manual talks about is ... with the ignition on but engine not started , a voltage of 450 mV should be present. I don't see any such quiescent voltage . Need help . Thanks , Bob

 

Forgot to say this is a 1996 Windstar 3.8L , 144k Miles and I think original Oxygen Sensors.

 

Believe this is normal for the Over-The-Counter handheld scanners. I see the same thing on my Son's 2000 Taurus w/3.0 DOHC, My 2004 Freestar w/4.2 and my friends 2000 Windstar w/3.8 with my Scan tool.