Mileage: 168,365 miles
The gear display of the Porsche Cayenne is abnormal.
Verify the fault after connecting the car. As stated by the customer, the
diagnostic instrument detects that the transmission reports a fault, and the
selector lever switch is grounded. Modules related to gear display include
transmission control unit, gear switch, gear selector switch, and transmission
valve body control unit. The gear selector switch is located under the cover of
the gear lever. After disassembling, it is found that there are obvious traces of water ingress. Measure according to the circuit diagram and find that the circuit is not faulty. It is suspected that the selector lever switch is damaged, and it
is recommended to replace it. After the replacement, the gear display was normal. After a test drive, it was found that the gear selector switch displayed normal.
The gear display of the meter was still the same as the fault phenomenon when
entering the store, and the diagnostic trouble code was not eliminated. At this
time, we thought these were two faults, and only one of them was ruled out. After re-diagnosing the vehicle and performing circuit measurements, no problems were found. It was suspected that the transmission control unit was the problem, and
the Cayenne transmission control unit was installed on the Touareg (the Touareg
and Cayenne are equipped with the same transmission), and everything was found to be normal in the Touareg, and the transmission control unit failure was
eliminated. The gear switch is suspected to have a problem, so a new gear switch
was installed. The fault remains after the switch is installed. At this time, the
diagnosis has reached a deadlock. As shown in Figure 1.
After installing the shift lever switch, we found that everything was normal (the shift lever switch base was not installed at this time). After re-installing the shift lever switch base the fault returned. We determined there must be an issue
with shift lever switch base. Through observation, it is found that there no
electrical connections on the shift lever switch base, only two small magnets. We realized during the previous disassembly and assembly process, there was a magnet attached to the maintenance tool. Could it be that the polarity of the magnet was mistaken during the installation? With this question, we readjusted the magnet and tested the car and the fault was eliminated.
Troubleshooting: Replace the shift lever switch and reinstall the magnet on the
Failure summary: This failure was caused inadvertently. We must be careful in the maintenance process, follow the "existence is reasonable" mentality, and treat
each component objectively.