Hello everyone, new to the forum. Just bought a 2003 CTS with a 3.2 and a 5L40e trans and of course, as soon as I bought it, it started shifting weird. When it'* cold and if I baby it, it will shift just fine through all 6 shifts (I'm aware this is a 5 speed, no need to get into technicalities, there is supposed to be 6 shifts). If I am harder on it, say shifting around 3500 rpms it will also shift perfectly through all 6 shifts. But driving normally shifting around 2200-2400 rpm, it will go 1,2,3 just fine, then going into 4th it will immediately just to "5th" and drop 1000 rpm'* and make it bog a little. If it'* like one of my dodge trucks, it will lock TC (essentially another gear) before going into it'* final gear or OD.

Question is this, with the 5L40e trans, what is the shift sequence? is it 1,2,3,4,TC lock, 5 like most of the dodges? Also, what sensors are used and whatever else to shift properly (crank position, speed sensor etc)? Where would be a good place to start with this? Personal I wouldn't be surprised if there is a knock off sensor in the car giving faulty info to the PCM or TCM so that it shifts weird. I had a 05 cummins that wouldn't shift into overdrive at all till I put an OEM TPS in it, the still working just fine knock off TPS from O riley'* made it not shift into OD even at 60+ mph.

Moved thread from the "General GM Chat" forum to the "Cadillac" forum.

How many miles on this car?

Is the transmission fluid fresh and full?

When was the last filter change?

A video of this would be nice.

I believe it will engage the converter clutch once in the highest gear allowed, either 4 or 5 depending on what is selected on the prindle, and requested power (throttle) is below a certain level . . . and both based on speed as well.

A bunch of sensors are "used", but really they are used by the PCM. Decisions are made based on mapping programmed into it, not like analog thresholds of long ago.

Fluid level and how recent the latest filter change was.

. . . then this would be a good place to start as well. Read telemetry from the car and see if everything looks right.

Does it have a check engine light on?

Are there any codes stored?

I'd have to know more about that situation to comment further, but don't want to jump down that rabbit hole. DaimlerChrysler was going through a lot back in those days, and still trying to figure out how to build solid automatic transmissions, especially behind the Cummins. We'll stick to diagnosing your Cadillac here.

What I meant when I said shifts is speeds. If you say gears everyone gets all up in arms over semantics because there'* only 5 forward gears even though it has 6 speeds.. So replace when I say "shifts" with "speeds" then that will make more sense.

It only has five gears. What you mistakenly call a gear is nothing more than the TCC locking up which just eliminates converter loss.
It is programmed to lock the converter at certain speeds and load in both forth and fifth gears.
Load is determined by TPS, VSS and MAF or Manifold vacuum.

I watched the video probably ten times. I didn't see anything unbecoming. The shift patterns are different based on detailed mapping based on engine load, vehicle speed, throttle input, ambient temperature, fluid temperature, etc.

How many miles on this car?

How many miles have you driven it?

Is the transmission fluid fresh and full?

When was the last filter change?

On the subject of shifts versus speeds versus gears: A five speed shifts four times from a dead stop to the tallest gear:

Shift 1: ratio 1 to ratio 2
Shift 2: ratio 2 to ratio 3
Shift 3: ratio 3 to ratio 4
Shift 4: ratio 4 to ratio 5

Since you can see the tach and know what it is telling you, you can see the moment that the torque converter engages. It looks like another shift but it is just the converter locking. The moment that it locks will be more or less of an RPM difference based on the ratio that is engaged, vehicle speed, throttle input, etc.

My advice (if there isn't a glaring symptom that I haven't seen): Keep driving it and see if these behaviors are consistent over a few thousand miles.