Guide to Repairing a PDK Transmission
09-11-2021, 04:45 PM
#631
Hey PV997,
So we finally got the customer's car with the P1706 issue and have been diving into it to confirm what's going on before possibly repairing the transmission. I had initially thought we would be looking at the pressure sensors based on most people's findings, but I believe we may have something else going on and wanted to get your insight.
P1706 is the only fault, and the actual values do indeed show 3V for the shared 5V reference while a direct check of pins at the control unit confirms 3V for the pressure sensor wire and 5V for the distance sensor wire. The control unit was replaced by a previous shop for this reason, but did not resolve anything.
Here's where things get interesting...
If we remove the pressure sensor 5V wire from the connector or disconnect the harness at the transmission, we still see 3V at the control unit pin.
But, if we remove the distance sensor 5V wire from the connector at the control unit, the 5V reference for the pressure sensor side shows normal instead of 3V. This is also true when you disconnect the transmission connector for the distance sensors.
Resistance readings also show similar across the pressure sensor pins, but inconsistent and vastly different across the distance sensors.
Our assumption is that there is a possible short or internal issue with the distance sensor pack, which is drawing from the shared 5V reference from the control unit, but we are not seeing any of the typical faults for distance sensors etc. I know P1706 tends to be directed at the pressure sensors, but the fault is also vague in the way that it covers the 5V reference for both sensor groups.
I've reached out to T-Design also to see if they have come across this specific issue before, but also wanted to throw it into the mix before we dive into this unit. My original plan was to replace the pressure sensors along with a T-Design sensor pack to cover any future potential failures, but I would like to make sure that we have our PDK ducks in a row beforehand on the off chance there is something I'm missing here.
So we finally got the customer's car with the P1706 issue and have been diving into it to confirm what's going on before possibly repairing the transmission. I had initially thought we would be looking at the pressure sensors based on most people's findings, but I believe we may have something else going on and wanted to get your insight.
P1706 is the only fault, and the actual values do indeed show 3V for the shared 5V reference while a direct check of pins at the control unit confirms 3V for the pressure sensor wire and 5V for the distance sensor wire. The control unit was replaced by a previous shop for this reason, but did not resolve anything.
Here's where things get interesting...
If we remove the pressure sensor 5V wire from the connector or disconnect the harness at the transmission, we still see 3V at the control unit pin.
But, if we remove the distance sensor 5V wire from the connector at the control unit, the 5V reference for the pressure sensor side shows normal instead of 3V. This is also true when you disconnect the transmission connector for the distance sensors.
Resistance readings also show similar across the pressure sensor pins, but inconsistent and vastly different across the distance sensors.
Our assumption is that there is a possible short or internal issue with the distance sensor pack, which is drawing from the shared 5V reference from the control unit, but we are not seeing any of the typical faults for distance sensors etc. I know P1706 tends to be directed at the pressure sensors, but the fault is also vague in the way that it covers the 5V reference for both sensor groups.
I've reached out to T-Design also to see if they have come across this specific issue before, but also wanted to throw it into the mix before we dive into this unit. My original plan was to replace the pressure sensors along with a T-Design sensor pack to cover any future potential failures, but I would like to make sure that we have our PDK ducks in a row beforehand on the off chance there is something I'm missing here.
09-11-2021, 05:24 PM
#632
Three Wheelin'
Thread Starter
Hey PV997,
So we finally got the customer's car with the P1706 issue and have been diving into it to confirm what's going on before possibly repairing the transmission. I had initially thought we would be looking at the pressure sensors based on most people's findings, but I believe we may have something else going on and wanted to get your insight.
P1706 is the only fault, and the actual values do indeed show 3V for the shared 5V reference while a direct check of pins at the control unit confirms 3V for the pressure sensor wire and 5V for the distance sensor wire. The control unit was replaced by a previous shop for this reason, but did not resolve anything.
Here's where things get interesting...
If we remove the pressure sensor 5V wire from the connector or disconnect the harness at the transmission, we still see 3V at the control unit pin.
But, if we remove the distance sensor 5V wire from the connector at the control unit, the 5V reference for the pressure sensor side shows normal instead of 3V. This is also true when you disconnect the transmission connector for the distance sensors.
Resistance readings also show similar across the pressure sensor pins, but inconsistent and vastly different across the distance sensors.
Our assumption is that there is a possible short or internal issue with the distance sensor pack, which is drawing from the shared 5V reference from the control unit, but we are not seeing any of the typical faults for distance sensors etc. I know P1706 tends to be directed at the pressure sensors, but the fault is also vague in the way that it covers the 5V reference for both sensor groups.
I've reached out to T-Design also to see if they have come across this specific issue before, but also wanted to throw it into the mix before we dive into this unit. My original plan was to replace the pressure sensors along with a T-Design sensor pack to cover any future potential failures, but I would like to make sure that we have our PDK ducks in a row beforehand on the off chance there is something I'm missing here.
So we finally got the customer's car with the P1706 issue and have been diving into it to confirm what's going on before possibly repairing the transmission. I had initially thought we would be looking at the pressure sensors based on most people's findings, but I believe we may have something else going on and wanted to get your insight.
P1706 is the only fault, and the actual values do indeed show 3V for the shared 5V reference while a direct check of pins at the control unit confirms 3V for the pressure sensor wire and 5V for the distance sensor wire. The control unit was replaced by a previous shop for this reason, but did not resolve anything.
Here's where things get interesting...
If we remove the pressure sensor 5V wire from the connector or disconnect the harness at the transmission, we still see 3V at the control unit pin.
But, if we remove the distance sensor 5V wire from the connector at the control unit, the 5V reference for the pressure sensor side shows normal instead of 3V. This is also true when you disconnect the transmission connector for the distance sensors.
Resistance readings also show similar across the pressure sensor pins, but inconsistent and vastly different across the distance sensors.
Our assumption is that there is a possible short or internal issue with the distance sensor pack, which is drawing from the shared 5V reference from the control unit, but we are not seeing any of the typical faults for distance sensors etc. I know P1706 tends to be directed at the pressure sensors, but the fault is also vague in the way that it covers the 5V reference for both sensor groups.
I've reached out to T-Design also to see if they have come across this specific issue before, but also wanted to throw it into the mix before we dive into this unit. My original plan was to replace the pressure sensors along with a T-Design sensor pack to cover any future potential failures, but I would like to make sure that we have our PDK ducks in a row beforehand on the off chance there is something I'm missing here.
The wildly varying resistance on the distance sensor is normal as you are looking into a semiconductor. The distance sensor may even work fine even if the voltage is pulled down low as many semiconductors are designed to work over a wide voltage range. So it's possible it could still give valid readings even if there was an internal short that caused a voltage drop.
The pressure sensor on the other hand simply provides a varying resistance proportional to the pressure. So if the supply voltage was low for it the resulting current measured by the TCU would also be low. It's conceivable the TCU interprets this as an out of range value and throws a fault.
I would try and measure the current being drawn by the distance sensor and see if it is excessively high. You may be able to do this with a current clamp or you could jumper it in at the connector (jumper the ground and use an ampmeter for the supply connection). I don't know what the distance sensor should draw but I would expect no more that a few hundred milliamps. You shouldn't need to jumper the signal lines as the distance sensor starts running once it sees power (though the TCU will throw errors).
09-11-2021, 07:06 PM
#633
Pretty interesting, sounds like the the load from distance sensor is causing a voltage drop that's affecting the pressure sensor. Obviously it shouldn't do that. Do you see the 3V on the distance sensor supply line too (measured when still connected)? If it's pulling down the line you would expect to see the low voltage in both places.
The wildly varying resistance on the distance sensor is normal as you are looking into a semiconductor. The distance sensor may even work fine even if the voltage is pulled down low as many semiconductors are designed to work over a wide voltage range. So it's possible it could still give valid readings even if there was an internal short that caused a voltage drop.
The pressure sensor on the other hand simply provides a varying resistance proportional to the pressure. So if the supply voltage was low for it the resulting current measured by the TCU would also be low. It's conceivable the TCU interprets this as an out of range value and throws a fault.
I would try and measure the current being drawn by the distance sensor and see if it is excessively high. You may be able to do this with a current clamp or you could jumper it in at the connector (jumper the ground and use an ampmeter for the supply connection). I don't know what the distance sensor should draw but I would expect no more that a few hundred milliamps. You shouldn't need to jumper the signal lines as the distance sensor starts running once it sees power (though the TCU will throw errors).
The wildly varying resistance on the distance sensor is normal as you are looking into a semiconductor. The distance sensor may even work fine even if the voltage is pulled down low as many semiconductors are designed to work over a wide voltage range. So it's possible it could still give valid readings even if there was an internal short that caused a voltage drop.
The pressure sensor on the other hand simply provides a varying resistance proportional to the pressure. So if the supply voltage was low for it the resulting current measured by the TCU would also be low. It's conceivable the TCU interprets this as an out of range value and throws a fault.
I would try and measure the current being drawn by the distance sensor and see if it is excessively high. You may be able to do this with a current clamp or you could jumper it in at the connector (jumper the ground and use an ampmeter for the supply connection). I don't know what the distance sensor should draw but I would expect no more that a few hundred milliamps. You shouldn't need to jumper the signal lines as the distance sensor starts running once it sees power (though the TCU will throw errors).
It wasn't until the distance sensor wire was removed in order to confirm the actual voltage output for that pin that we noticed the pressure sensor side went back to normal. This was then duplicated with the wire reinstalled, and entire harness connector for the distance sensor side then disconnected at the transmission.
Last edited by Ptech1; 09-11-2021 at 07:08 PM.
09-12-2021, 10:51 AM
#634
Three Wheelin'
Thread Starter
We do not. The supply line for the distance sensor reads normal (5V) at all times, even while the pressure sensor supply reads 3V. Since both rows of pins can be removed separately from the connector, we started checking things individually to see if there was a wiring issue. Nothing changed the 3V reading initially as we were doing an entire harness check based on a dealer tech we know having an issue with a harness causing similar faults due to a connection issue.
It wasn't until the distance sensor wire was removed in order to confirm the actual voltage output for that pin that we noticed the pressure sensor side went back to normal. This was then duplicated with the wire reinstalled, and entire harness connector for the distance sensor side then disconnected at the transmission.
It wasn't until the distance sensor wire was removed in order to confirm the actual voltage output for that pin that we noticed the pressure sensor side went back to normal. This was then duplicated with the wire reinstalled, and entire harness connector for the distance sensor side then disconnected at the transmission.
I would want to confirm the distance sensor is causing this prior to replacing it as the T-design part is not cheap and you are not seeing the classic fault codes. As I mentioned above, measuring the distance sensor current draw would be a good first step to see if the hypothesis makes sense.
We don't know for certain how the 5 volt supply is generated inside the TCU but it very likely has a voltage regulator followed by a current limiting resistor. The distance sensor, the pressure sensors, and the temp sensor all use a 5 volt supply. Perhaps there are separate circuits or it uses the same one shared for all three. The latter seems more likely based on the symptoms you describe. However if that was the case, we would expect to see the low voltage on all three of them, not just the pressure sensor.
Edit: BTW, the TCU has the 5 Volt supply on two pins, B19 and B20. The fact that they are next to each suggests they come from the same voltage regulator (though not certain). One of those wires then goes to each of the two PDK connectors. The lower PDK connector 5V goes just to the distance sensor. The upper PDK connector 5V splits to both the two pressure sensors and the temp sensor.
Last edited by PV997; 09-12-2021 at 11:14 AM.
09-12-2021, 04:46 PM
#635
Just to clarify, the distance sensor supply line read 5 Volts even when the distance sensor was connected? I'm asking as I don't see how the distance sensor could be pulling down the voltage for the pressure sensor without pulling down it's own voltage supply also. Something doesn't make sense here.
I would want to confirm the distance sensor is causing this prior to replacing it as the T-design part is not cheap and you are not seeing the classic fault codes. As I mentioned above, measuring the distance sensor current draw would be a good first step to see if the hypothesis makes sense.
We don't know for certain how the 5 volt supply is generated inside the TCU but it very likely has a voltage regulator followed by a current limiting resistor. The distance sensor, the pressure sensors, and the temp sensor all use a 5 volt supply. Perhaps there are separate circuits or it uses the same one shared for all three. The latter seems more likely based on the symptoms you describe. However if that was the case, we would expect to see the low voltage on all three of them, not just the pressure sensor.
Edit: BTW, the TCU has the 5 Volt supply on two pins, B19 and B20. The fact that they are next to each suggests they come from the same voltage regulator (though not certain). One of those wires then goes to each of the two PDK connectors. The lower PDK connector 5V goes just to the distance sensor. The upper PDK connector 5V splits to both the two pressure sensors and the temp sensor.
I would want to confirm the distance sensor is causing this prior to replacing it as the T-design part is not cheap and you are not seeing the classic fault codes. As I mentioned above, measuring the distance sensor current draw would be a good first step to see if the hypothesis makes sense.
We don't know for certain how the 5 volt supply is generated inside the TCU but it very likely has a voltage regulator followed by a current limiting resistor. The distance sensor, the pressure sensors, and the temp sensor all use a 5 volt supply. Perhaps there are separate circuits or it uses the same one shared for all three. The latter seems more likely based on the symptoms you describe. However if that was the case, we would expect to see the low voltage on all three of them, not just the pressure sensor.
Edit: BTW, the TCU has the 5 Volt supply on two pins, B19 and B20. The fact that they are next to each suggests they come from the same voltage regulator (though not certain). One of those wires then goes to each of the two PDK connectors. The lower PDK connector 5V goes just to the distance sensor. The upper PDK connector 5V splits to both the two pressure sensors and the temp sensor.
Last edited by Ptech1; 09-13-2021 at 09:51 AM.
09-13-2021, 09:38 AM
#636
Three Wheelin'
Thread Starter
CORRECTION: I spoke in detail with the technician who was diving into this and he stated that both 5V signals were 3V until you disconnect either the distance sensor line or that entire connector at the transmission. I misunderstood or misheard this while going through it, so this may change things even while the distance sensor circuit being removed/disconnected makes the rest of the system happy (disconnecting pressure side does not change anything).
I will work on the current draw readings for the distance sensor and checking the temperature sensor seeing as how you mentioned it is on the same 5V as the pressure circuit to see if that sheds any light as we ran out of time on Fri. But I agree, replacing the sensor pack without solid answers isn't how we spend our client's money, let alone while dealing with grey areas we haven't seen before based on a single fault.
I will work on the current draw readings for the distance sensor and checking the temperature sensor seeing as how you mentioned it is on the same 5V as the pressure circuit to see if that sheds any light as we ran out of time on Fri. But I agree, replacing the sensor pack without solid answers isn't how we spend our client's money, let alone while dealing with grey areas we haven't seen before based on a single fault.
Based on what I know about the distance sensor internals I would not expect a properly functioning unit to draw more than 100 mA (high estimate). Will be interesting to see the results of your current draw test.
09-13-2021, 09:55 AM
#637
Ok, that makes much more sense based on how the TCU likely develops the 5V supply voltage. That voltage is current limited inside the TCU and once something in the circuit draws excessive current the voltage sags for all components sharing it. I think you are right that it's the distance sensor or the PDK-internal harness for the distance sensor that has a short.
Based on what I know about the distance sensor internals I would not expect a properly functioning unit to draw more than 100 mA (high estimate). Will be interesting to see the results of your current draw test.
Based on what I know about the distance sensor internals I would not expect a properly functioning unit to draw more than 100 mA (high estimate). Will be interesting to see the results of your current draw test.
We have now also checked for amperage draws across those individual circuits and see less than a few milliamps of draw with no real differences between them, so nothing shows odd there as far as we can tell.
All logical and physical signs point to the distance sensors, or as you stated, the harness internally. I just hate working in grey areas while committing to costly repairs with no proof of a solid draw other than seeing the 5V signal effected.
Last edited by Ptech1; 09-13-2021 at 09:57 AM.
09-14-2021, 10:55 AM
#638
PDK 7DT45 Gear selector sensor
7DT45/PDK PDK 7DT45 Automotive Transmission Gear Switch Sensor
This sensor is the same on the models Porshe
Boxster /Cayman /Carrera/911
Part No. 0501325775
Chassis WPOCA2988CS710612
Do you have the part in stock?
Price in Dollars?
Post to Brazil?
WhatsApp Brazil
55 11 96115 1111
WhatsApp Brazil
55 11 91118 9061
Mr Hect
7DT45/PDK PDK 7DT45 Automotive Transmission Gear Switch Sensor
This sensor is the same on the models Porshe
Boxster /Cayman /Carrera/911
Part No. 0501325775
Chassis WPOCA2988CS710612
Do you have the part in stock?
Price in Dollars?
Post to Brazil?
WhatsApp Brazil
55 11 96115 1111
WhatsApp Brazil
55 11 91118 9061
Mr Hect
09-14-2021, 11:23 AM
#639
Basic Sponsor
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I believe we are in communication via email...
PDK 7DT45 Gear selector sensor
7DT45/PDK PDK 7DT45 Automotive Transmission Gear Switch Sensor
This sensor is the same on the models Porshe
Boxster /Cayman /Carrera/911
Part No. 0501325775
Chassis WPOCA2988CS710612
Do you have the part in stock?
Price in Dollars?
Post to Brazil?
WhatsApp Brazil
55 11 96115 1111
WhatsApp Brazil
55 11 91118 9061
Mr Hect
7DT45/PDK PDK 7DT45 Automotive Transmission Gear Switch Sensor
This sensor is the same on the models Porshe
Boxster /Cayman /Carrera/911
Part No. 0501325775
Chassis WPOCA2988CS710612
Do you have the part in stock?
Price in Dollars?
Post to Brazil?
WhatsApp Brazil
55 11 96115 1111
WhatsApp Brazil
55 11 91118 9061
Mr Hect
__________________
T-Design9 : Mods and ergonomic accessories bespoke designed for Porsche cars
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T-Design9 : Mods and ergonomic accessories bespoke designed for Porsche cars
Memory Modules : remember SC **** settings; A/S/S, PSE, Spoiler, Sport/+ buttons
Phone Mounts : keep your phone up and close and charged
Cupdholders, Sunglass Holsters and more at T-Design9.com
09-14-2021, 12:09 PM
#640
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Yes, it's the worst. Usually PDK repairs are pretty straightforward after error codes are known. But one in a million times we get this
09-14-2021, 12:20 PM
#641
I want to buy the sensor from T-Design9 but refuse to provide the Company's public record Please show the legality of the company, answer these questions 1) EIN = company registration to appear in the STATE sphere and the federal taxpayer number. 2) The TAX ID + ITIN of the business owner 3) The Social Security Number (SSN) 4) the record that does not contain debt in the name of the company
I want to buy the sensor from T-Design9 but refuse to provide the Company's public record Please show the legality of the company, answer these questions 1) EIN = company registration to appear in the STATE sphere and the federal taxpayer number. 2) The TAX ID + ITIN of the business owner 3) The Social Security Number (SSN) 4) the record that does not contain debt in the name of the company
09-14-2021, 10:38 PM
#643
Three Wheelin'
Thread Starter
We had initially checked/disconnected the temp sensor signal also during our initial search for a draw seeing as it was on the same connector, and it made no difference in seeing the 3V.
We have now also checked for amperage draws across those individual circuits and see less than a few milliamps of draw with no real differences between them, so nothing shows odd there as far as we can tell.
All logical and physical signs point to the distance sensors, or as you stated, the harness internally. I just hate working in grey areas while committing to costly repairs with no proof of a solid draw other than seeing the 5V signal effected.
We have now also checked for amperage draws across those individual circuits and see less than a few milliamps of draw with no real differences between them, so nothing shows odd there as far as we can tell.
All logical and physical signs point to the distance sensors, or as you stated, the harness internally. I just hate working in grey areas while committing to costly repairs with no proof of a solid draw other than seeing the 5V signal effected.
At the risk of turning this into a science project, there is one more thing you might want to consider. I would disconnect the lower PDK connector (the one that goes to the distance sensor) and install a jumper for every populated pin between the harness and connector (there are 9 populated total). This makes it act as if the connector is attached and function normally. Then measure the 5v line on the pressure sensor and remove the jumpers one by one until you find the one that when removed makes the voltage go back up to 5V. Shut the power off and reinstall the jumpers except replace the one you found on the previous step with a multimeter set up to measure current (not in parallel with the jumper but inline in place of the jumper). This will tell you exactly which line is the culprit and how much current is being pulled through it. You can connect and disconnect it a few times to ensure all the measurements are repeatable.
If you don't see excessive current there then I'm at a loos to explain it.
09-15-2021, 05:41 PM
#644
Unless there is something wrong with the TCU (which I think you said the previous mechanic replaced) I don't see how the supply voltage can be pulled down low unless *something* is drawing excessive current. I think you are right that all signs point to the distance sensor but it sure would be nice to have more compelling evidence.
At the risk of turning this into a science project, there is one more thing you might want to consider. I would disconnect the lower PDK connector (the one that goes to the distance sensor) and install a jumper for every populated pin between the harness and connector (there are 9 populated total). This makes it act as if the connector is attached and function normally. Then measure the 5v line on the pressure sensor and remove the jumpers one by one until you find the one that when removed makes the voltage go back up to 5V. Shut the power off and reinstall the jumpers except replace the one you found on the previous step with a multimeter set up to measure current (not in parallel with the jumper but inline in place of the jumper). This will tell you exactly which line is the culprit and how much current is being pulled through it. You can connect and disconnect it a few times to ensure all the measurements are repeatable.
If you don't see excessive current there then I'm at a loos to explain it.
At the risk of turning this into a science project, there is one more thing you might want to consider. I would disconnect the lower PDK connector (the one that goes to the distance sensor) and install a jumper for every populated pin between the harness and connector (there are 9 populated total). This makes it act as if the connector is attached and function normally. Then measure the 5v line on the pressure sensor and remove the jumpers one by one until you find the one that when removed makes the voltage go back up to 5V. Shut the power off and reinstall the jumpers except replace the one you found on the previous step with a multimeter set up to measure current (not in parallel with the jumper but inline in place of the jumper). This will tell you exactly which line is the culprit and how much current is being pulled through it. You can connect and disconnect it a few times to ensure all the measurements are repeatable.
If you don't see excessive current there then I'm at a loos to explain it.
We went back into the car yesterday and had the same thoughts you mentioned above, singling out each individual wire even though we had previously seen that disconnecting any of the position sensor wires did not change the 5V system (still seeing 3V). During a discussion, I was looking at the sensor ground provided by the TCU and questioned whether there could be resistance or shorting issues on the ground side causing a draw from the 5V source.
We rechecked voltage across the distance sensor 5V circuit again using both the sensor ground and a good chassis ground, with both showing the same, or approx 3V.
We then removed the sensor ground wire from the harness connector in order to confirm it separately and found 5V existed there, but only while disconnected. A check of the 5V wires/system also showed a normal 5V reading with this ground wire removed. With it reinstalled, there is no voltage present, but a continuity check to ground now shows a definitive short. It didn't show previously, but it may have just been a poor connection or simply missed it. Either way, when all else fails, go back to the basics and prove it!
The order has been placed with T-Design, and we will be inspecting the harness to ensure there are no issues with it as well. But the assumption is that the simple harness is probably ok, while the more complicated sensor pack would have circuitry that would allow for an internal short more easily.
Attached are pics of the distance sensor readings we were getting yesterday also. A conversation with Vlad led to this appearing to once again be a sign of an internal sensor issue, and/or a generic reading due to the calibration failing with the new TCU installed previously.
The interesting thing is that the values were all identical, aside from position 3, which read the exact opposite polarity depending on whether the 5V wire for the distance sensors was connected or not. Figured I would share with the class on the off chance someone runs into the same issue or data in the future.
Last edited by Ptech1; 09-16-2021 at 12:07 AM.
