PDK Failure
01-16-2015, 04:43 PM
#31
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Thread Starter
I'd like more information from the OP. I am most curious to know if he tried to shut down and restart before he had the car towed.
The reason I ask is that these cars are so dependent on the computer brain that most of the faults I have experienced with my car have been cured by a simple re-start. And yes, I have had the red transmission failure light on my dash and the car would not move. I have had that error between five and ten times and each time, a re-start cured it--meaning it is very obviously a minor electrical glitch and not a mechanical failure.
The dealer "could not duplicate the problem", meaning that there was not a code directing the helpless tech straight to the part he needed to replace, and the issue has not occurred in over a year.
And yes, I replaced my battery about a year ago and most of my electrical gremlins went into hibernation.
The reason I ask is that these cars are so dependent on the computer brain that most of the faults I have experienced with my car have been cured by a simple re-start. And yes, I have had the red transmission failure light on my dash and the car would not move. I have had that error between five and ten times and each time, a re-start cured it--meaning it is very obviously a minor electrical glitch and not a mechanical failure.
The dealer "could not duplicate the problem", meaning that there was not a code directing the helpless tech straight to the part he needed to replace, and the issue has not occurred in over a year.
And yes, I replaced my battery about a year ago and most of my electrical gremlins went into hibernation.
On the first attempt, it worked and I drove it around the neighborhood for a few minutes. Once I shut it down again, it refused to go into gear no matter what.
01-16-2015, 04:51 PM
#33
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Thread Starter
I also have a '66 912. My 997 is my DD and I love it but when I want to drive around with a grin on my face, I take the 912 out and enjoy the smell of burning oil and the sound and fury of all 8 valve thrashing about and solex carbs popping away. Pure Porsche bliss!
01-16-2015, 04:59 PM
#34
Rennlist Member
But, consider the financial implications to Porsche as it stands now. If the slightest defect requires a replacement of the whole $14k component, that's a pretty sweet motivation to not train techs, to build the thing sealed and with non-replaceable components and to make car warranties dependent on replacement versus fixing.
Another poster suggested that in the future Porsche should consider offerring remanufactured units to reduce the cost. Maybe I missed this, but aren't the replacement transmissions being offered today remanufactured/
01-16-2015, 05:58 PM
#35
Rennlist Member
01-16-2015, 10:00 PM
#36
Nordschleife Master
I'd like more information from the OP. I am most curious to know if he tried to shut down and restart before he had the car towed.
The reason I ask is that these cars are so dependent on the computer brain that most of the faults I have experienced with my car have been cured by a simple re-start. And yes, I have had the red transmission failure light on my dash and the car would not move. I have had that error between five and ten times and each time, a re-start cured it--meaning it is very obviously a minor electrical glitch and not a mechanical failure.
The dealer "could not duplicate the problem", meaning that there was not a code directing the helpless tech straight to the part he needed to replace, and the issue has not occurred in over a year.
And yes, I replaced my battery about a year ago and most of my electrical gremlins went into hibernation.
The reason I ask is that these cars are so dependent on the computer brain that most of the faults I have experienced with my car have been cured by a simple re-start. And yes, I have had the red transmission failure light on my dash and the car would not move. I have had that error between five and ten times and each time, a re-start cured it--meaning it is very obviously a minor electrical glitch and not a mechanical failure.
The dealer "could not duplicate the problem", meaning that there was not a code directing the helpless tech straight to the part he needed to replace, and the issue has not occurred in over a year.
And yes, I replaced my battery about a year ago and most of my electrical gremlins went into hibernation.
01-18-2015, 01:07 PM
#37
On the precision of the wire lengths etc...sort of unrelated, but it taught me about the very high tolerance requirements for signal timing on high end electronics. I own a boat and it has an autopilot. Per the installation instructions, the installer/repair may not lengthen or shorten the control head wiring harness leading to the brain of the unit (read that splice). Apparently the unit is set up to perform at a very specific signal interval (i made that descriptor up but you get what i mean).
If there is a splice added to the wiring harness, then it changes the timing of the signals and is very bad for the performance of the unit. My guess is that the gear lever is the control head in my example and the brain is inside the PDK. I would assume that this has something to do with the repair. And, when we repair the auto pilot unit, we have to replace either of the parts (head or brain) in its entirety. I am certain (not being an engineer) that my suggestion isn't exactly correct, but maybe conceptually it is.
If there is a splice added to the wiring harness, then it changes the timing of the signals and is very bad for the performance of the unit. My guess is that the gear lever is the control head in my example and the brain is inside the PDK. I would assume that this has something to do with the repair. And, when we repair the auto pilot unit, we have to replace either of the parts (head or brain) in its entirety. I am certain (not being an engineer) that my suggestion isn't exactly correct, but maybe conceptually it is.
01-18-2015, 01:55 PM
#38
Signal timing concerns over lengths of cable went away with analog signals. I wouldn't doubt if this "one sensor replacement" statement really is based on not enough slack in the harness (obviously some careful splicing could get around this). As far as that autopilot cable, their concern has to do with an installer adding a failure point in the form of a poor splice and/or extending the cable with the wrong type.
01-18-2015, 08:51 PM
#39
Rennlist Member
EE here. Propagation delay through a wire is about 1ns (a billionth of a second) for every 6 inches. Porsche's electronics aren't *quite* that precise (my guess) at least in terms of timing. However, the temp sensor could be an analog one and it's possible the TCU is making very precise measurements with a precision ADC, perhaps on the order of microvolts or microamps (or less). If the wire is too long or if the connection (crimping) isn't excellent, the measurement could get thrown off either by impedance mismatch or noise coupling.
This would make a great reverse engineering project, but in the meantime I'll just hope one blown sensor doesn't result in an entire transmission going kaput.
This would make a great reverse engineering project, but in the meantime I'll just hope one blown sensor doesn't result in an entire transmission going kaput.
01-18-2015, 09:59 PM
#40
Nordschleife Master
EE here. Propagation delay through a wire is about 1ns (a billionth of a second) for every 6 inches. Porsche's electronics aren't *quite* that precise (my guess) at least in terms of timing. However, the temp sensor could be an analog one and it's possible the TCU is making very precise measurements with a precision ADC, perhaps on the order of microvolts or microamps (or less). If the wire is too long or if the connection (crimping) isn't excellent, the measurement could get thrown off either by impedance mismatch or noise coupling.
This would make a great reverse engineering project, but in the meantime I'll just hope one blown sensor doesn't result in an entire transmission going kaput.
This would make a great reverse engineering project, but in the meantime I'll just hope one blown sensor doesn't result in an entire transmission going kaput.
01-18-2015, 10:01 PM
#41
Nordschleife Master
I did shut it down and re fire it multiple times, checked the fuses, disconnected the battery, put it on a charger and did an interpretive dance over the hood.
On the first attempt, it worked and I drove it around the neighborhood for a few minutes. Once I shut it down again, it refused to go into gear no matter what.
On the first attempt, it worked and I drove it around the neighborhood for a few minutes. Once I shut it down again, it refused to go into gear no matter what.
01-18-2015, 10:50 PM
#42
Advanced
Thread Starter
Agreed, The dealership where I bought the car (Non Porsche) put a VW battery in it without telling me because the original was dead. I need to confirm that the battery is within Porsche specs. If not, there may be recourse there.
01-18-2015, 11:05 PM
#43
The battery tester I have is a series of plates (to dissipate heat) and operates a lot like a toaster. If you have access to one of these you can take the above voltages before and after stressing it.
01-26-2015, 08:51 PM
#44
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Thread Starter
Update
Update: The new PDK is at the dealership but they found a leaky seal at the flywheel so we're waiting for that to be shipped from Atlanta and then it'll go back together. Hoping to have it home by the end of the week.
01-26-2015, 09:27 PM
#45
Rennlist Member
Did you noticed any oil on the floor?