My
2008 Boxster
Tiptronic has been throwing up TPC sensor code issues as well as Check engine light P0741. It all happened after I drove the car for a while with the wrong sized rear
tires
kn the car. The
tires
were smaller than they should be, this alone constantly threw up the TPC sensor issues from day one. My cousin (a
Porsche
Mechanic) who put the
tires
on said it should be fine or that the TPC sensors may need to be replaced. After driving for a few months the check engine light with P0741 came up, but no transmission symptoms. I figured it must be something to do with the TPC miss reading the wrong sized
tires
for so long and the CPU not adjusting to it and thinking the wheels were spinning faster than they should based on the TPC readings it must have been getting. I've since replaced the rear
tires
with the proper size and the sensors still won't read properly. I've pulled the
battery
multiple times for 10 seconds but the codes cup right back on on start up. But based on what I've seen in the comments it needs to sit unplugged for longer, and that I would need to go into the menu system of the car to reset the TPC sensors.
That said I eventually got it checked out by a
Porsche
shop that confirmed nothing mechanically is wrong with the car and the TPC sensors are fine. That the software apparently needs to be reset, something only
Porsche
is able to do. Now the car is at a
Porsche
dealer and classic repairshop waiting for them to get back to me.
Any suggestions?
Hi, welcome to Planet-9, the friendly
Porsche
Forum!
A few suggestions (and questions probably):
- I'm moving this post to the correct forum. You found the right section (987) but wrong container.. will move this to a troubleshooting subforum. Hang on.. OK - we're there.
- TPC = ?? I assume you are referring to the tire pressure monitoring system (
TPMS
in
Porsche
language), and the TPC you refer to are tire-pressure-sensors (TPS in
Porsche
talk..)? Since I'm assuming this, I'll continue with the assumption.
- TPS (aka TPC) has nothing to do with telling anything about the rolling speed of the wheels/
tires
.
It's a completely separate system.
- Wheel speed sensors DO tell the ABS/PSM module about the rotational speed of the wheels. If there is a large discrepancy (like a wheel sliding due to ice) the PSM system will use the ABS functions on the ABS/PSM hydraulic system to control the wheel spin by applying the brake on the spinning wheel. As a general rule - these systems are most happy when the rolling diameter of the tires is the same, front and back. That means different size tires
can
be used -
providing the rolling diameter is the same
(via taller/lower sidewall, etc.)
- P0741 - Isn't listed in my Porsche code tables for 2009, but that makes sense since 2009 had PDK, and your car has a Tiptronic (aka - slushbox) that has a torque-converter, and a torque-converter clutch (used to lock-up the torque converter improving MPG and reducing emissions..) Anyway - that code indicates the torque converter is misbehaving, and it's possibly the torque-converter lockup clutch. Different size rolling diameters will have absolutely no effect on this - so the mismatched tires weren't to blame.
Here is what Porsche has to say about that error when it occurs on a Cayenne - which also is "Tiptronic":
P0741 Symptoms
Check Engine Light will illuminate
Vehicle will not shift into the highest gear at freeway speed
Decrease in fuel economy
In unusual cases, there are no adverse conditions noticed by the driver
In some cases, there may be performance problems, such as dying when coming to a stop after driving on the freeway and/or misfire-like symptoms
Common Problems That Trigger the P0741 Code
Defective Torque Converter Lockup Solenoid
Defective Engine Coolant Temperature Sensor
Defective Torque Converter Clutch
Defective Valve Body
Dirty transmission fluid that restricts the hydraulic passages
Common Misdiagnoses
Engine Misfire problem
Internal Transmission problem
Driveline problem
Note that I highlighted two items - the
check engine light
illuminates - check!
Dirty transmission fluid
- that's where I'd start. Do a complete fluid change, drive it 1,000 miles, then do it again. This isn't real cheap since the fluid is pricey, but it's WAY less expensive than replacing the transmission. The reason I say do it twice - you only get about half the fluid out of a Tiptronic when you change the fluid, so the new fluid is immediately contaminated by the old fluid. Doing it a second time reduces the amount of contamination. To really change it ALL - requires the disassembly of the transmission, since the fluid is trapped in the torque converter and valve passages.
Now the questions -
- When you refer to the "codes" immediately reappearing on startup - what "code" do you mean? Are you getting a TPMS (Tire-Pressure-Monitoring-System) warning, or are you getting the check engine warning? Chances are - if it's a TPMS warning, your sensors are dead (kaput, passed-on..) If it's the check engine warning - you'll get that since the problem with the transmission won't fix itself.
- BTW - disconnecting the battery won't erase stored OBD-II codes. Doesn't work that way. That was back in the very early days before OBD-II. OBD-II is designed to store these sort of codes until a tool is used to erase them after the perceived problem is fixed. Obviously, the dealer can do this - but so can you if you buy the right tools (I'd suggest reading our diagnostics subforum
Porsche Diagnostics and Programming
about Porsche capable scanning tools.)
Since the dealer has it now - chances are - they'll come up with something expensive, like a new/rebuilt transmission that costs about 2/3rds of the value of the car. You may want to search for an independent shop specializing in Porsches. Your local PCA chapter would be the place to ask about one.. The independent is more likely to think about trying to save your transmission, whereas dealers are programmed to simply replace it (they won't repair them..) If a new transmission is required, I'd search for a good used one (eBay always has some) - these aren't troublesome transmissions so the prices used aren't awful.
Good luck - and let us know how it's resolved.
So I've heard back from the Dealership nd was told exactly what you predicted. They recommend total transmission replacement. And are even telling me the soft top is now stuck even though it was functioning as I used it on driving it there.
