Is Relay Needed to Install Brake Controller in 2015 Porsche Cayenne

Updated 07/30/2018 | Published 07/28/2018

Question:

I have seen that a relay is no longer needed when installing a P3 brake controller into a 2015 Cayenne diesel. Is this still true? Thanks!!

asked by: Jon B

Expert Reply:

There are special requirements for installing a brake controller on a 2005 to present Porsche Cayenne. This includes your 2015 Porsche Cayenne diesel. You will need the following parts that are available from a Volkswagen dealer.

1 connector housing (#1J0-972-782) and
2 wire/terminal assemblies (#000-979-228)

Cut the wires from both wire assemblies in half so that you have 4 wires, each with a clip on one end and bare wire on the other. Connect the bare end of each of these wires to one of the wires on your brake controller, then slip the other end of each wire into its appropriate slot on the housing. The slots are numbered to make it easier to connect each wire correctly. The table in the linked help article shows the correct wiring connections.

The factory brake control connector is located under the vehicle's dash on the driver's side close to the door. You'll have to remove the appearance panel, which is held on by 2 Torx head screws. The factory brake control connector is underneath the panel and is wrapped in gray foam. Remove the foam and connect the housing to the connector.

You will likely need to install a relay if you're using a Prodigy or P3 brake controller # 90195. The display of these controllers can be erratic when used on 2009-current Volkswagen Touregs and Porsche Cayennes. To avoid this problem, you should install a 12V, normally open relay. Instructions and numbered diagram in the linked article will help you install the relay correctly.

1 Obtain locally, a 12 volt, normally open relay.
2 Connect the ground terminal (85) of the relay to a ground under the dash.
3 Connect the trigger terminal (86) of the relay to pin #3 of the brake control connector.
4 Connect the red wire from the brake control to the load terminal (87) of the relay.
5 Connect the source voltage terminal (30) to a 12 volt source. This wire should have a 5-amp fuse installed in-line.