Yes it should in theory, as it will only go to 4th IF the correct solenoids activate. So by return logic it would drop to 1st if B were to switch oft, as it's then changing the flow of auto fluid.
That's the thought train I was following. However I've changed all the solenoids, which fixed the problem for 3 months.
am I right in saying the problem occurs when in auto Drive (when cruising at constant speed on level ground in 4th) but doesn't happen when manually selecting gears using Command Shift and leaving it in Command Shift when cruising?
It's tricky to answer that, as the fault is so completely random.
However it seams to manifest itself when in D, and the box is going up to 4th, or dropping down to 4th.
If so that would suggest failure caused by it detecting it needs to change gear, as opposed to something like solenoid B dropping out.
I thought it was a TCM issue, once it did it 3 months after I'd changed the solenoids.
If it does happen when using Command Shift then that theory is dead, but it means a random drop out of solenoid B could still be the cause (or result affect of something causing that).
However it has done it in Command Shift to, although only once I think.
I have found that using CS does seem to reduce its occurrence, although maybe not, as it's so random.
I do know that when it's done it's thing and dropped to 1st, using CS doesn't help the box change up to 2nd, even though the LCD shows 2, the box remains in 1st. If I keep driving as a steady speed in 1st, the box will all of a sudden change up. If it does this up change in CS 2nd, then the up change is smooth, providing the revs are kept under control.
However if I'm being cross with it because it's stuck in 1st while D is selected and I'm revving the nuts off the engine. When the box changes up, it does so without any torque reduction, and thumps in really hard. This causes the F4 to flash, and the box locks in 4th, after which it'll drive all day and cause no more issues. Now my thinking says, if No4 solenoid was faulty, it couldn't stick in 4th and stay there.
This is making me wonder if there's a hardware problem with the gearbox, and not an electric fault at all.