AT OD flashing at idle

[fixkick]

the needle is bad,in the meter, (it has bearings there) or the cable is binding up. (2 ways)

if the cable binds, up's it jerks too. (rust, bad, frayed, or kinked, they jerk)

if the speedo make s funny sound, that is the needle bearings shot(in the meter behind the MPH needel)
if how ever, the meters is silent while the bouncing, then mostlikely the cable jerks (bad cable)

and if the TCM is using the meter, VSS1 sensor, the TCM will report this as VSS error.

the TCM on the G16 car, uses 2 VSS sensors the meter side VSS2, and the trail shaft. VSS1 (a master VSS and back-up VSS (a fact)

if the trans tail shaft VSS fails, the TCM sets a DCT error for IT ,and now uses the cluster VSS (OSS alternate) but if both VSS go dead, then shifting ends. no more upshifts.
i have no TCM schematics for J18s. zero.
that link above, has them. if go there. (mitchells)

but in any case, TCM needs to know vehicle, speeds. (out put speed of trans)
if the TCM can not KNOW, true speed, how can it shift?,. answer it cant, or if the VSS is flaky, the shifting will be erratic. as one might expect....

find the tail shaft VSS, remove it , clean it and put it back, might cure this problem.
they all (tail sensor only) gather metal dust and from a metal mud on the tip (magnet it is ) and then fails. clean off that mud and magic can happen.
with no scan tools, just looking can find this.
but that is just wild guessing, of the large numbers of things the A/T systems can do.