So I put new Bosch O2 sensors in this weekend and now the UG is showing an open loop, which according to the user's manual indicates the system is not reading the sensors, and my around-town mpg dropped like a stone from 10-12 to 5-6. Full tank, same 93 octane, same station. Ideas, thoughts, condolences?...

 

possibly needs to go through a obd readyness/drive cycle period before operating again if your comp decided to lol. what kind of short and long term fuel trims are you seeing? are you getting data from all 4 o2's, and are they steady or changing rapidly? doubel check for exhuast leaks?

 

Not certain but from my experience, you need to drive enough to reset the ECU with the new sensors. The first time I replaced mine my mechanic friend told me to get on the highway for 40 miles and drive at 50 mph not 48 not 52 but 50. This allows the ECU to read and reset itself. If yo do stop and go traffic you are not allowing your ECU to read the system long enough to do a reset. Atleast thats what I had to do.

 

You will get a check engine light soon.
You need to check the plug connections.
One is most likely loose.
You had to reach way up there and I bet the plug did not snap in.
Or if it did - it was not really snapped in cause the garage was cold and the plastic is brittle in the cold.

 

thanks guys. always ran with a closed loop b/f new sensors. how to check for exhaust leaks, cigar?

 

You will only get open loop cause the sensor is:

Disconnected
or
bad - just plain bad from Bosch.
or
The sensor is not getting hot enough from the exhaust.

If you have noise from your exhaust manifold or a loose Y pipe, you need to clean up all those problems first.

 

if you have an ultra guage make a page w all 4 o2's, and see what kind of data they are putting out cold start to full temp... sensor 1's are precat (front), sensor 2s are postcat (rear), bank 1 are drivers side, bank 2 are passenger side. sensor 1's are used for fuel trim, sensor 2s are to check on the condition of the cat's.

 

sweet, thanks GK, hadn't thought of that.

 

I posted elsewhere... Got Bosch o2s not long ago and the front two were bad. Brand new. I went nuts trying to figure out wiring and ended up putting new o2s in and they immediately worked.

Also be sure your connectors are clean and put a little dielectric grease on them.

 

thanks Charlie. set up the U/G to read the O2 inputs. Short 1 was reading from about -6 to like 20, Short 2 had no reading (will double-check the connection), Long 1 and 2 both just sat on 25.0. still haven't had time for a long drive, but now that I know there's no bank 2 reading, that can wait til after I get that resolved. thanks guys.