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Porsche Cayenne Keyless Entry System not work

One Porsche Cayenne made in year 2010 with 35 thousands mileage, the driver described: the remote control locks and unlocks function can work, but Keyless Entry System not work.

Porsche cayenne

After connect the vehicle: I have a basic test on the car, firstly I insert the key into the key hole and pull driver's side door handle, the door has no starting sign, then I pull the other three doors I got the same result. Finally, I stop the car in the garage troubleshooting platform, and efficiently isolate the interrupting signal from outside, again I did the same work as I did just now, it still have troubles.
Firstly, let us have a basic knowledge on how it works. Porsche Cayenne Keyless Entry System integrate RFID into the car key, when the driver take the key to near the car, as long as the driver's hand near the door handle the RFID system in the door will be activated. At this time RFID transceiver will scan the area around the car to identify and find out the specific ID code in the key RFID chip, once the code is found out, transceiver will confirm the chip valid or not by security algorithm and decide whether open the doors. Once the car owner identification is confirmed, the system will confirm whether the keys is in the car, if it is, the car owner only need to press the Starting button, the car will start; when the driver take the key away from the car, the door and steering wheel will automatically lock, the windows will automatically rise up, the car is in the anti-theft status. Both this system and the traditional remote control immobilizer system can be used.

I use fault code scanner: Porsche Piwis Tester II to test keyless entry system control unit (Kessy), and find a trouble code 0183-inner antenna fault, currently exist. As I know many cars have the same problems, at this time the keyless entry system can work, but to my surprise, after I change back the old antenna, the keyless entry system can still work. After clearing the trouble code, I drive the car on the road, the trouble don’t appear again. Then I ask the driver go on observing,
Several days later, the fault occurs again. I use the Porsche Piwis Tester II to enter and input signal to measure, and read out the door handle sensor data, when my hand close to the door, it display  "No Start", it should display  "Starting". Then I test key password, Kessy power supply and driver's door power sensor, they all can work. In order to confirm Kessy power voltage, I remove it and test the voltage on the premise of additional simulated load, the result is the voltage has no problem. Then the fault should exists in the inner antenna and Kessy.
Then I test the antenna Resistance value in the front and the back of central control platform, also the luggage antenna Resistance value, they are all 7ΩResistance value, it has no problem. For caution's sake, I change all inner antennas and test this Resistance value, the trouble still exists. So far, I confirm, the trouble exists in the Kessy.
Troubleshoot trouble: I change Kessy according to maintenance manual, after lock the car for 5 min I try to start the car, and I find the keyless entry function is not working, the remote controller unlock button and lock button function is opposite, the starting machine can't work. Then I use PIWIS II enter setting / control unit learning function, and match the car key and Kessy,after successfully match, keyless entry function and remote controller button can work. I try to start the engine, it immediately turn off, I try again, no react, then I use Piwis Tester II to read out engine control unit  (DME) trouble dump, the trouble code is 0513 immobilizer system key is not correct, currently exist. According to boot failure inquiry, I know the anti-theft lock program in the DME is not correct. Then I use trouble code scanner enter into DME to do anti-theft program, then start the engine, it can successfully start. Later this trouble code does not occur any more, the trouble is solved.

Conclusion: when I diagnose the fault for the first time, it is not easy to find out where the fault is because the fault disappears soon. As for this occasional fault, it needs enough time to observe. If the fault does not influence driving safety, the driver can observe when driving, requesting the driver record some information about the fault, including: time, frequency, symptom, place, climate and more, these information will be very helpful for  our technician.

When I diagnose the fault for the second time, the fault keep exist, so I can one-by-one check parts that may have fault from the small part to the bigger part, from the simple one to the sophisticated one, until I find out the part which has fault.
Fault Conclusion: if the car leakage, you are expected to step-by-step check the reasons starting from the bus tread, you are not suggested to aimlessly disconnect all fuses or control unit, and you’d better use Current Clamp to test.