ronegarnett

My car: 2001 996 C4 Cabriolet, Approximately 110K miles. It had the 0740 error along with a bunch of others. The car would go into Limp Mode and it felt as if it were slipping in 3rd gear only. P0733 Gear sel. monitor 3rd gear P0734 Gear sel. monitor 4th gear P0740 Solenoid Valve - torque converter clutch P1585 Fault lateral acceleration / speed from PSM P1574 Porsche code 364 - Stop light switch signal implausible Short Story and Current State: I ordered a ZF solenoid / regulator kit, carefully replaced all 7 parts and had one new one left over. I'm curious as to why there was one left - Is it supposed to go somewhere else? Now, I'm only getting the 0740 and a different, more basic stop light switch signal that comes on occasionally and kills ABS when it does. That may be a red herring. Will try another switch. On the fluid: I filled with Pentosin, started the car and ran through the gears. Then I stopped, checked/refilled, and ran through the gears again. Then, I checked/refilled it and drove it a bit to make sure the fluid got everywhere it was supposed to get before a final check at the proper temperature. The only symptoms I'm getting in the transmission are somewhat abrupt shifting, mainly into 3rd but sometimes maybe into 2nd. I've tried the quick 3 pumps of the accelerator trick and that does alter the shifting. I'm not sure it fixes it, though. Sometimes it seems less abrupt, but I haven't nailed down that scenario yet. I haven't had the shift points recalibrated, so that's a potential action. Any other ideas, insights, etc.? Long Version (TL;DR): A stack of symptoms led to a set of maintenance tasks which I performed starting in November of 22. Symptoms going in: Strange clunk under the rear seat when hitting or coming off the gas Clicking noise from the front end when turning right Routine brakes and oil change needed Somewhat rough idle ABS light coming on sporadically The shifting was somewhat heavy --- Solved: It was a torn transmission mount. I didn't see it on initial inspection and pursued #5 until I figured it out, then replaced that and the motor mounts. Clunk gone. I made my own tool for pressing in the new trans. mount. It worked but was painful. Solved: I discovered a very shot front, passenger-side CV axle while changing the differentials' fluids, and replaced it. Also a couple of linkages were worn so I replaced them. Solved, Obvious. Improved: Put in new plugs and coil packs. Ongoing: Replaced the stop light switch, but still getting the same error Ongoing : I dropped the pan, put in a new filter, and filled with a Febi product that is supposed to be proper. I also changed the fluid in both differentials. The initial fluid that came out was dark grey as I recall. In the bottom of the pan was a bit of sludge but I didn't see any metal shavings when I cleaned all the magnets. Once back together, I started noticing the 3rd gear revving up unusually at times so didn't drive it much while I researched. I made the mistake of putting a gasket varnish/sealant on the new pan gasket, the kind you paint on. Apparently it didn't seal too well. After noticing significant leakage, I once again dropped the pan to replace the gasket, and filled it back up. I didn't see any seal or sealant fragments in the pan. That time, I used Pentosin. It seemed to get worse after that, though. Still slipping in 3rd and then limp mode started popping up. At this point, I took it to a Porsche tech I trust. He said I needed a new valve body for only $5400 + installation. Ouch. I pondered sending the valve body off to be rebuilt, but decided to try the ZF solenoid and regulator kit instead after talking to both that shop and another. That takes us back to the short story at the top. Very drivable, but need to figure out the P0740 before declaring it road-ready.