Chasing an SES light...

[Muleears]

So, should I reset using the 510 or disconnect the battery for a while? I reset the adaptations for the trans and it made a positive change in driveability. I don't know if I can remember how to get there (on the 510)...

[Muleears]

This morning I excavated my UltraGauge from the garage and plugged it into the X as I went to the landfill. I immediately got the "pending trouble code" alarm. When I got back I plugged in the NT 510 and used the plain OBDII function. It told me I had a pending code of P1093 "Pre catalyst fuel trim system too rich bank 2" I then switched to the BMW function and it found the code "EC DME Trimming, Oxygen sensor before Cat. bank 2". Sounds like the downstream sensors are acting up, or at least I'm being told that...

I then searched until I found where to reset the adaptations, which I did. At this time, even with the pending codes, I don't have the SES light, but I haven't driven very far either. I will drive more today and we'll see if these become hard codes or if clearing the adaptations does away with them (thank you andrewwynn). I will report back with findings at some point later today. Merry Christmas to everyone.

UPDATE: I have driven as far as it took to trip the light before and no light as of yet. So I cleared the pending code so now I have a clear memory. We'll see how long it takes to pop up again, if ever.

[andrewwynn]

The pre cat code will set as pending for one drive cycle and set the SES light the second cycle.

Check your realtime live data for fuel trim and you should see values under ten percent for short term and long term values in the range of 0.02-0.06ms.

Yours was reading rich mine was lean but same issue. I believe the DME learns the current state of the wear of the front O2 sensors and when they are suddenly different the computer thinks that is an error because it's assuming the same sensors are there.

[Muleears]

Originally Posted by andrewwynn

I believe the DME learns the current state of the wear of the front O2 sensors and when they are suddenly different the computer thinks that is an error because it's assuming the same sensors are there.

And this is why resetting the adaptations solves the problem? The DME learns the state of the new sensors and has nothing to compare it to so it adopts the new readings as the norm and, no error? Just trying to understand...

Thanks, you have been very helpful. Merry Christmas!

[andrewwynn]

I had a very different but related problem with the post cat sensors that gave me fits for months with heater errors even though the current was within spec the whole time.

I think the problem was very similar in that the computer was used to the original sensors and when I replaced them and suddenly the heater resistance was different the DME thought something failed.

Nothing I could find could fix the repeating error, but I tried something out of desperation: unplug the sensor completely (actually I was doing to determine which bank it was).

When I plugged back in magically no more heater error. I think that finally told the computer to recalibrate the new sensor. I unplugged both, started car waited for both to error. Plug back in clears codes and never got another heater error.

If you don't have scanner that can reset fuel I'm betting the same trick will work for reset the front sensors.

[Muleears]

At the moment... I have no codes. Time will tell though. I need to drive it 170 miles tomorrow. That should trip something if it is going to. If it trips on the way over (to my daughters, 85 mi.) I'll reset them as you suggested while there and see what happens on the way back. Thanks again for the info.

[andrewwynn]

I'm pretty confident. I chased the same exact bug for several weeks and since reset put 400/500 miles on no error and 15/20% better mpg as a hell of a bonus. Reset before your trip and monitor the fuel trims on the trip you can pull up live with NT510

[andrewwynn]

Originally Posted by Muleears

And this is why resetting the adaptations solves the problem? The DME learns the state of the new sensors and has nothing to compare it to so it adopts the new readings as the norm and, no error? Just trying to understand...



Thanks, you have been very helpful. Merry Christmas!

That's my theory. The long term stored values are erased and the computer starts from scratch and learns the new sensors behavior.


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[Muleears]

Not only was the trip to my daughters a success socially, I didn't get an SES warning either. 175 mile trip plus 40 miles in to work this morning would have lit the light if it was going to. Thank you andrewwynn and Overboost for the direction.

[andrewwynn]

I'm halfway through my 450 mile Christmas trip and no error for me but my mpg has been not great so I'm suspecting my MAF is worn out. I'm going to swap with wife's and see if things improve before I order a new one.