P0740 error, poor shifting when cold, no speedo!

[Jinster]

My Boxster has a problem of not having any speed signal with both the ABS and Spoiler warning light on.

The CEL light is NOT on. The transmission 4th Gear light is NOT on, either.

Now, the car has also been shifting poorly lately especially when cold. It lurches and slips and the gears don't engage or downshift properly. It is still driveable, but only if carefully shifting. The problem is more marked when driving gently. It seems to be masked when driving aggressively (the delay in shifting and slip between gears become less noticeable to me).

Having spent heaps of money on my Boxster last year alone, I have decided to trouble shoot this one myself. So I bought a OBD2 scanner.

It didn't return any speedo signal related codes!

It did return a P0740 which is "torque converter solenoid circuit open".

I am guessing that this means the torque converter is not engaging properly due to this solenoid not switching it right.

I have two questions for those in the know:

1. What is the most likely cause/fix to this P0740? Is replacing the solenoid a start and can that be DIY?

2. Can this P0740 also relate to the lack of speedo signal problem which surprisingly doesn't seem to show any related codes at the moment?

The scanner I used is from http://www.obd-2.com/

Please help. The last thing I need now is a transmission replacement. It's a 1997 Boxster with 120kkm on it. No tiptronic service yet as far as I know.

[wvicary]

I repair lots of tranny problems by just cleaning the electrical connections.... sometimes just unplugging then plugging them back in will do the trick. Have you check the codes for the ABS?? It might help to narrow down the problems, you might just have no speed signal. I wouldn't rush into replace the solenoid as it could very well be just a poor connection. A very similar transmission is used in VW and Audis which I've worked on for several years.... if a solenoid is suspect, we just trade places in the valve body with another solenoid to see if the problem follows that solenoid. Check your ABS codes and let us know what you find.

[Jinster]

Thanks for your reply, Sir.Rhosisoftheliver.

My OBD2 scanner doesn't give ABS codes. It only gives P codes (DTC, Mode $03) and some "non-uniform core" codes (Mode $07).

The P0740 is all I get at the moment.

I was told that there are 4 speed sensors, one in each wheel. And they all go to the ABS controller which monitors the 4 sensors for consistency.

I have no speed signal visible on the dash at the moment.

I don't think my scanner can read individual speed sensor actual voltage.

Is the solenoid accessible from just under the car or do I have to take apart the tranny? I will try to unscrew/unplug it if it's easily accessible.

[JFP in PA]

You code is definitely the torque converter clutch circuit......and electrical issue.