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UPDATE: The Google Nexus 6P comes with a USB-C to USB-A cable that you need to connect to your car's dashboard or head unit. I have made the necessary changes in this post. The Nexus 5X does not include this cable.
Google announced two new Nexus phones in September of last year - Nexus 5X and Nexus 6P. Both devices feature plenty of new features including fingerprint sensors and faster processors. The phones are also the only two devices that come pre-installed with Android 6.0 Marshmallow, Google's latest software.
With Marshmallow, users get access to Android Auto. I recently got my hands on a Nexus 5X for the purpose of testing it out with my Pioneer AVH-4100NEX which supports Android Auto. Although you would think getting Android Auto working would be a simple plug-and-play operation it isn't.
If you are planning on upgrading your smartphone to the Nexus 5X to be able to use Android Auto right out of the box, you may want to read this first.
Google Nexus 5X and Android Auto
The problem with using Android Auto on a Nexus 5X
USB-C is a new connector that gained popularity when Apple announced the new MacBook last year. The connector has several advantages over other USB connections ranging from faster data transfer to the ability to connect reversibly like Apple's lightning connector.
The Google Nexus 5X comes with a single USB-C charging cable. The cable has USB-C connectors at both ends though, because the charging block included also features a USB-C port. So if you're planning on using this cable to connect to your car dashboard, forget about it.
What you need...
It is highly likely that your car features a USB-A female port for connecting your smartphone. To this, you connect your phone's USB cable. Aftermarket head units, like the Pioneer AVH-4100NEX which supports Android Auto, also features a USB-A female port (USB Port 2 in this case).
To connect a Nexus 5X to your car or head unit, you will need a USB-C to USB-A cable. When USB-C was first announced, these cables were quite expensive and not widely made. But these days, it is relatively easy to find one.
I found this cable that worked really well and is very well priced (around $10). It's the Qube Gadget USB Type C to USB Type A 3.0 cable.
The cable is USB 3.0 and backwards compatible to USB 2.0 so you should be good to go when using it with older devices. Even if you aren't getting a new Nexus phone, it might make sense to have a couple of these cables handy because USB-C is poised to gain popularity in the coming months with more devices supporting the protocol.
The Qube Gadget cable is thick and features a reinforced nylon casing. The nylon ensures the cable is resistant to cracking or even tangling. The connectors are made from aluminum. The cables come in Gold and Silver color options.
With the correct cable, Android Auto from a Nexus 5X worked great. There are no known advantages to using Android Auto on a Nexus 5X compared to other smartphones but the USB-C connector is supposed to be faster. But the USB-A connection would still be a bottleneck to any visible speed differences.
I also have a Nexus 5 which I've been using for my Android Auto needs before I got the 5X. I haven't seen any differences between the two devices when it comes to Android Auto so far.
Here are some other USB-C to USB-A cable options you can also consider. I haven't personally tested any of these cables but judging by the reviews on Amazon you should have no issues getting them to work. All these cables are USB 3.0 or later so you should be future proof...