Most of the PDK threads and discussions have been focused on replacing the distance sensor. While it is a common failure mode there are other failure modes. Additionally, we strongly believe in confirming the failure before going through the effort/cost of replacing a sensor (or if you go to the dealer the whole transmission!). We've seen too many people spending thousands of dollars using the shotgun approach. Many times this is done without definitively determining the cause of the failure, just because it’s the most common failure mode. This page is intended to assist in proper diagnosis of PDK issues before replacing parts attempting to prevent using the shotgun method whenever possible. The information provided below is based on lessons learned while repairing a number of cars with PDK issues and assisting other owners doing so as well as being a part of the research and development effort that resulted in the JUMPS distance / speed sensor pack. In any case, we welcome feedback from owners / workshops willing to share their data / experience to maintain this write-up as the go-to place for PDK troubleshooting.
Fault Codes / Data
Fault Codes and real time data are the main tools for determining the failure but there are several things that can be checked using a standard Multimeter. There are several alternatives to a PIWIS that can read the fault codes and perform other actions (calibration, fill etc.). However, it appears that these do not provide the subtext for the fault code and associated data like the PIWIS does. Each code has several different sub-modes, knowing this is important in determining the actual failure. We also recommend using the USB interface, versus WiFi, when doing critical tasks such as calibration and software updates. While the Wifi interface is super convenient during regular troubleshooting activities it sometimes results in loss of communication (timeout) during longer processes such as calibration.
Calibrations
We see a lot of recommendations to run a calibration to cure various PDK issues. I’m not aware of a single case where a calibration has resolved a fault code There are however many examples of unnecessary calibrations causing failures / bricked TCU (especially the Calibration with Parts Replacement). The only time we’d consider running a calibration, other than following a part replacement, is if there are jerky shifts. In this case the calibration (without parts replacement) may result in an improvement.
There is no reason why a calibration shouldn’t pass the first time. If it doesn’t, you likely have an issue with the transmission (sensor) or the PIWIS adapter. The Calibration With Parts Replacement should only be run if the valve body is replaced. For sensor replacements the Calibrations Without Parts Replacement is sufficient and recommended. This one calibrates the Shift Rod Position Sensors and the Clutch (calibration is not needed following Speed Sensor replacement).
Distance Sensor
A failed shift rod (SR) distance sensor is the most common issue withe these units and is typically indicated by a 1731, 1732, 1733 or 1734 fault code. While the code is a strong indicator of a failure it’s advisable to 100% determine the failure mode before investing time and money in replacing the sensor pack. This is normally easy to do, a reading deviating from the following with the transmission in P on the indicated sensor would be quite conclusive. Additionally, a sensor reading 0.0 (without any dither) or >9 mm (+ or -) has almost certainly failed.
A P1764 or P1765 may also post as a result of a distance sensor failure. These codes indicate that the shift rod did not reach the intended position and the gear was therefore not selected (locked out). While the failure could also be caused by a physical obstruction or hydraulic system failure an "in-range" failure of the distance sensor would have the same effect.
Example of a failed sensor showing 11.5mm deflection
Pin out of the Lower Connector (from the wire side)
SR1 (green - pin 7) 0mm (+/- 1mm)
SR2 (white - pin 8) 0mm (+/- 1mm)
SR3 (gray - pin 9) 0mm (+/- 1mm)
SR4 (yellow - pin 10) 8mm (+/- 1mm) (This may be -8mm)
What if I don't have a PIWIS?
If you don’t have a PIWIS or equivalent you can use a regular volt meter. First verify good supply voltage, there should be 5VDC between Ground (pin 13) and Supply (pin 12) then measure between ground (pin 13) and each sensor; 2.25 to 2.75 VDC would be acceptable for SR1-3 and 3.75 to 4.25 VDC or 0.75 to 1.25 VDC would be OK for SR4. Anything >4.5VDC or less than 0.5VDC would indicate a a failed sensor. Note that needle style probes are needed to reach the pins from the back of the harness side housing. Insulated mini crocodile clips are useful for measuring the pins with the connector detached..
What if I don't get a consistent fault code?
Random failures or failure during startup can be caused by an internal failure in the distance sensor bringing the supply voltage down or by a failing battery. This can result in other codes than those listed above, such as P1706. The best way to confirm this type of failure is to measure the supply voltage (pins 12 and 13) during start and steady state (engine running). Any drops below 5 VDC are suspicious. Seeing codes not related to the PDK also indicate a battery issue. Measuring the battery voltage during start is also helpful, too much of a drop will result in these types of failures (drops below approximately 9 VDC cause issues). If anywhere near these values, have your battery checked at the local auto supply store. If a short in the sensor is suspected, disconnect the lower connector on the transmission and measure resistance between supply (pin 12) and ground (pin 13). The resistance should be approximately 135 kOhm. Significantly lower indicates a failed distance sensor that may be bringing down the voltage.
Temperature dependent issues
As with many other sensors, issues often only occur at high temperatures. If the failure can not be confirmed at room temperature, consider repeating the measurements with the transmission warmed up to operating temperature.
Transmission Control Unit (TCU)
While failures of the TCU seem to be rare there have been a case reported where a TCU provided a too low 5V supply and associated fault codes when cold. When the TCU warmed up the supply voltage corrected itself. This was repeatable. Probably not a common failure mode but something to check for if dealing with supply voltage issues.
Speed Sensors
Speed Sensor issues are typically identified by fault codes P0730, P1743, P1744 and P1745. According to the Porsche Flowchart you may also see other codes such as P17F0, P17F1, P17F2, P17B5, P17B6, P17B7 and P17B8. In addition to these, codes such as P173E and the Over Temp codes (P17F0, P17F1 and P17F2) may be observed. If the only code posted is P0730 Porsche recommends checking for PSM codes. Similar to the DIstance Sensor and DME codes, it is recommended to address any PSM codes before the PDK codes.
Pressure Sensors
A pressure sensor failure can typically be identified my measuring the impedance. If you disconnect the connector (at transmission or TCU) and measure the sensor the impedance should be:
Signal to Supply: 9.2 MOhm
Signal to Ground: 8.1 kOhm
Supply is pin 13 (pin 20 at the TCU)
Ground is pin 14 (pin 3 at the TCU)
Sensor 1 Signal is pin 11 (pin 30 at the TCU)
Sensor 2 Signal is pin 12 (pin 31 at the TCU)
Supply voltage (pins 20 to 3) should be 5.0V. Output is a voltage.
As the pressure increases, the Signal to Ground voltage increases, and the Signal to Supply decreases.The sum of the output measured between Signal and Ground and the output measured from Signal and Supply always totals the Supply voltage (5V).
Examples:
Before start:
Supply to Sensor 1 = 4.5V Ground to Sensor 1 = 0.5V.
After start but no pressure applied at clutch
Supply to Sensor 1 = 4.4V Ground to Sensor 1 = 0.6V
Clutch pre-filled but not fully engaged.
Supply to Sensor 1 = 4.15V. Ground to Sensor 1 = 0.85V
Clutch fully engaged
Supply to Sensor 1 = 4.1V. Ground to Sensor 1 = 0.9V.
Temperature Sensor
The temperature sensor is a simple device that changes resistance as the temperature changes. You can monitor the measured temperature using PIWIS or simply measure the resistance between ground (pin 14) and sensor (pin 10) and compare to ambient using the chart. Look for unreasonable or erratic readings. Consider monitoring during warm-up to normal operating temperate. Note that the over-temperature codes often posts a s a consequence of another underlying issue. If there are additional codes, address this first.
Valve Body
While failures of the valve body and the attached solenoids seem to be rare there has been at least one instance where replacing it has corrected the issue of small cyclic rpm changes during cruise. The failure mechanism is not fully understood but it is believed that wear of an internal component or fluid contamination prevented smooth, accurate movement affecting clutch control. If seeing this behavior, it may be worth doing a flush to see if it corrects the issue before replacing the valve body.
Non PDK issues
There are a number of on-PDK issues that will trigger PDK fault codes. This seems to happen when there is a fault that could affect the ability of the DME to control the engine as needed by the PDK. One common example is a MAF failure (P1090). Always address DME fault codes before the PDK codes.
Other Resources
Here's another video frm Jeff Richardson that provides additional insights in determining an Electrical fault with the PDK.