Fault Code P0740

[dscheff]

I have a US 2000 Boxster S Tiptronic with 57K miles.

Recently, as I was driving at around 55 MPH, it would seem like the trasmission was downshifting. The RPM would go up about 100 or so and stay there. If I paddled down and then back up the RPM would settle back to around 2200 or so. It only did this in M mode.

My Porsche dealer ran a diag that produced an OBD P0740 code, and topped up with .5 QT of fluid. According to the Error Code the max temp in the transmission was 224.6 F. They found no leaks, but made a note that the fluid was dark gray to black. After test driving the vehicle, and finding no abnormal condition, they suggested I only use it in auto mode during normal driving to reduce stress on the transmission.

Now, of course, it seems to be doing it in auto mode - probably just my imagination ;o)

Has anyone had any experience with this condition? Is it a sign of imminent failure of the torque converter and/or transmission? Can the torque converter be replaced, or is a whole new transmission unit required?

(I am having the transmission fluid replaced next week.)

Thank you

Dscheff

[Loren]

P0740 Fault, torque converter clutch - present

Possbile causes:

- ATF supply

- Torque converter

- Pressure regulator 4 (hydraulic)

- Electrical triggering to pressure regulator 4

- Hydraulic control unit

[mickf]

The tip on my '01 S has done all things you describe, including the occasional P0740, for the past couple years which covers over 30,000 miles and about 100 autocrosses. I notice the RPM change when cruising and whether in M or D, often when the highway changes from level to uphill. Almost like a mini-downshift. If it does it while autocrossing it can't be noticed -- but the P0740s do seem to appear following a particularly brutal autocross.

The good news is that it doesn't seem to get worse -- it's just there to annoy me. Also, it doesn't seem to adversely affect my autocrossing.

The worst part to me is how it demonstrates the woeful lack of Tiptronic expertise that seems to exist. My dealership has spent hours on it and came up with nothing except to watch it. Other shops I talk to, well, you can see their eyes glazing over.........

I eventually decided to stop stressing over it and to think of it as a feature -- slightly lower gearing when dictated by load on the drive train! :cursing: Who knows, maybe it's giving me a gearing advantage in competition.

[dscheff]

Thanks for your replies :)

I have been driving the car a lot: which accounts for the delay in replying... Exactly what you described is happening. I am only worried about it breaking down miles from anywhere as we tend to "see where that road goes" a lot. The car drives as it always has: great, and I have noticed no other "gremlins" popping up.

The tip on my '01 S has done all things you describe, including the occasional P0740, for the past couple years which covers over 30,000 miles and about 100 autocrosses. I notice the RPM change when cruising and whether in M or D, often when the highway changes from level to uphill. Almost like a mini-downshift. If it does it while autocrossing it can't be noticed -- but the P0740s do seem to appear following a particularly brutal autocross.

The good news is that it doesn't seem to get worse -- it's just there to annoy me. Also, it doesn't seem to adversely affect my autocrossing.

The worst part to me is how it demonstrates the woeful lack of Tiptronic expertise that seems to exist. My dealership has spent hours on it and came up with nothing except to watch it. Other shops I talk to, well, you can see their eyes glazing over.........

I eventually decided to stop stressing over it and to think of it as a feature -- slightly lower gearing when dictated by load on the drive train! :cursing: Who knows, maybe it's giving me a gearing advantage in competition.

[dscheff]

Well. It's been another while since my last post. A change of tires later the car is still performing like a champ. The "mini-change" seems to be a bit more pronounced when the drivetrain is cold: that could be my imagination though.

Porsche said there was no need to change the tranny fluid until the required mileage: so I guess they are either not too worried, or they have a Tiptronic transmission with my name on the box hidden away somewhere ;)

I love this car!

2000 Boxster S

Tiptronic running on Michelins

[GranburyChuck]

Well. It's been another while since my last post. A change of tires later the car is still performing like a champ. The "mini-change" seems to be a bit more pronounced when the drivetrain is cold: that could be my imagination though.

Porsche said there was no need to change the tranny fluid until the required mileage: so I guess they are either not too worried, or they have a Tiptronic transmission with my name on the box hidden away somewhere ;)

I love this car!

2000 Boxster S

Tiptronic running on Michelins

I have had the same problem as you and the others mention. My perception is that there is something wrong with the lock-up portion of the torque converter. I think solenoid 4 controls this. My fluid has been changed by the dealer. They checked it and level was okay. got the P0740 code after a couple of track days. Cleared it and never see the code in daily driving but the slight downshift persists. Another member justed mailed me that he was going to have a tech drive with him with the computer connected to see how the solenoids were working.

[dscheff]

Well. It's been another while since my last post. A change of tires later the car is still performing like a champ. The "mini-change" seems to be a bit more pronounced when the drivetrain is cold: that could be my imagination though.

Porsche said there was no need to change the tranny fluid until the required mileage: so I guess they are either not too worried, or they have a Tiptronic transmission with my name on the box hidden away somewhere ;)

I love this car!

2000 Boxster S

Tiptronic running on Michelins

I have had the same problem as you and the others mention. My perception is that there is something wrong with the lock-up portion of the torque converter. I think solenoid 4 controls this. My fluid has been changed by the dealer. They checked it and level was okay. got the P0740 code after a couple of track days. Cleared it and never see the code in daily driving but the slight downshift persists. Another member justed mailed me that he was going to have a tech drive with him with the computer connected to see how the solenoids were working.

I'm due for a transmission service in a few miles. The car has performed very well so far. I think sometimes it shifts up and down a little more than others: that could also just be my imagination. The tech-connected computer road trip sounds like a splendid idea. I will try it with mine and post the results...

[dscheff]

So meanwhile it's 2013. In the meantime I had a water pump go bad, but the car is still running like a champ. The transmission still does the little downshift every now and then. The dealership says the same thing, "keep an eye on it". I love this car!