Thread: 03 model L322 TD6 GEARBOX

There could be a few explanations for this; low battery, low oil in gearbox, faulty switch/solenoid in the valve body, faulty/dying torque converter. Has the g/box ever had an oil and filter change ? sometimes this will cure the problem. It seems oil pressure in the box is down, hence the quick Command Shifts don't allow for the pressure to drop away on the change. I would check the battery and oil levels (look at the condition of the oil) first then probably get the codes read,before g/b service. The gearbox needs to be flushed, not cheap considering the cost and the quantity of oil used (around 20 litres).
Just be sure that whoever looks at it are aware of the quirks of the GM 5L40-E Transmission.

Good Luck

Originally Posted by jx2mad

When running up through the gears it sits in 4th and revs quite high before eventually dropping into 5th after I take my foot off the go pedal

Jim, are you sure it changes from 4 to 5 at this point or it is the Torque Converter going to Full Lockup?
In Auto mode mine will go into 5th anywhere as early as 60 (depending on throttle position), then the TC will go to partial lockup. Full lock up will only occur when the foot is eased (no matter what speed), by habit I usually lift at about 80 and then bury it again once locked. The TC will not goto Full Lockup under moderate to heavy load, it can’t make the transition smoothly, so will wait unit the throttle is eased – that is by design. The TC has multiple stages of lock up.

Originally Posted by jx2mad

.Also, when in command shift and I pull up, the box only drops back to second.

I assume you mean that it will only drop to 2nd on its own? Same as mine, and as I read it, that is correct. While operating in manual mode the TCU will down shift for you only to prevent damage to components, it is safe to lift off from standing in 2nd, it is up to you to select 1st if you want it – remember you are in MANUAL Mode, the TCU only makes a shift change (effectively overruling the driver) to prevent damage – it doesn’t want you to lift off in 3rd , so if you are cruising in 5th and come to a stop without changing down it will do so to a safe gear, which is 2nd.

Originally Posted by jx2mad

Recently it has gone back to the old habbit again.

To me your description (apart from the last sentence) seems as per normal, the TCU loads and operates very different shift maps for the different modes, so you cannot compare Manual Mode to Auto to Sport and even Cruise modes – the transmission will behave vastly different in each of the 4 driver selectable modes, not to mention the extra 4 non-selectable modes. Also it is important to remember that the TCU is adaptive, so changes in behaviour compared to directly after a service and reset would be expected, in "learns" your driving style.

Obviously I can’t comment on your transmission without comparing it, however if you are convinced that it is now behaving vastly different than before further investigation is required and Laurie's suggestions are a start.