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Yes, it doesn't know that the tcase is in low, just what the output shaft speed into the case is.
Ex: tcu thinks youre going 40 but youre really going ~15.
The transmission valve body switches hydraulic fluid into the appropriate channels and enables the overdrive gear set in the transmission instead of 1/2/3. And yeah, the TCU isn't even aware of the transfer case's existence, there's no signal wire from the 4x4 indicator lamp to the TCU and iirc the TCU is the same part number (for any given year) between 2x4 and 4x4 vehicles anyhow.
It seems that you guys are confusing TC lock with 4th gear(OD), OD is just that another gear just like 1st, 2nd and 3rd. Also it was my understanding that the TC won't lock when in 4wd so this would mean that the TCU somehow knows it's in 4wd? When the TC locks in 4th or 3rd the rpms lowers because of the reduced slippage of the TC when locked.
The tc WILL lock in 4wd, I do alot of
4wd driving in winter. I've also gone fast enough in low to lock it.
Like Ken said, the tcu doesn't know the transfer case is there.
I've never seen the TQ lock in 4x4 but I've always been going too slow and had my foot way too far in it to let the TCU even think about doing that when I'm in 4x4, so I can't really say much there :gee:
Acts exactly the same whether its in 2 or 4, high or low.
Its michigan, I've had 3 dd cherokees with the aw4, I've done lots of 4wd driving at normal road speeds. Even 80 on the highway (stupid, I know.)