Contour Enthusiasts Group Archives Forums General Troubleshooting Who knows their stuff about Long Term and Short Term Fuel Trim on OBD-II?

I work in the department that contains the OBD-II feature designers and calibrators and I write tests that the assembly plants use to test a variety of engine controls. While I've done relatively little with fuel trim directly (other than explain to plant repairmen what the likely causes of lean and rich errors are for their vehicles), I've seen that most vehicles stop trying to adapt at +/- 25-30% errors. Personally, I a bit suspicious of how the scan tool is displaying what it is reading from the PCM. What scan tool are you using and does it have an option to display data in raw versus engineering units?