Wondering why your car's USB port isn't charging your phone? You're not alone. It happens all the time and it's one of the more common questions we get.
Here's one question we got from a reader about this issue:
Are built-in car USB ports supposed to charge phones? My new car came with a USB port, and I thought it would be cool to just use that instead of plugging a USB charger in my cigarette lighter like I did in my old car. But when I plugged in, the phone didn’t charge. I didn’t look too closely, so it might have kept the charge even, but I think that the charge on the phone actually dropped while I was driving like it wasn’t even plugged in.
If your car USB port isn’t charging your phone, the problem could be with the port, the cable, or even the phone. Not all car USB ports are designed to charge phones, or power peripheral devices at all, so there’s a chance that you’re dealing with that type of situation. There’s also a chance that there is a compatibility issue between the port and your phone, which may or may not be solved by using a different cable.
The Strengths and Weaknesses of USB Phone Charging in Cars
USB is great because it’s a standard that pretty much everyone has picked up, so you can use the same cables to connect a whole bunch of different things. The problem is that while USB is capable of transmitting both power and data via the same connection, not every USB port is wired to do that. And even if a USB port is designed to provide power, minor differences in the way that some companies, like apple, handle USB charging can get in the way.
When USB was first introduced, the initial standard allowed for two different versions of USB ports: data ports and powered data ports. USB data ports only transmit data back and forth between a device and a computer, while powered data ports transmit both data and power. This is why some devices, like hard drives and scanners that draw power through a USB connection, have to be plugged into specific USB ports to work.
USB Data Connections in Cars
In some vehicles that include a USB port, the port is only designed to transmit data. This type of USB port typically allows you to plug in a USB flash drive to listen to music or install firmware updates, and you may also be able to plug in a smartphone or MP3 player to listen to music. Since this type of port only uses the data connection terminals and not the power terminals, it isn’t capable of powering any type of peripheral or charging your phone.
If you are unsure whether or not your vehicle has a data-only USB port, and it doesn’t say one way or the other in your owner’s manual, there are a few ways to check. The easiest is to try a variety of USB cables and devices to see if any of them show a connection to power.
USB Data Cables Versus Charging Cables
The USB standard specifies a configuration of four terminals numbered one through four. Terminals one and four transmit power, while terminals two and three transmit data. Most USB cables are just straight connections between the terminals on one end of the cable and the terminals on the other end, which allows the cable to transmit both data and power.
Data only cables totally omit terminals one and four, and power only cables omit terminals two and three.
However, the situation is actually a little more complicated than that. In order for a computer, or some infotainment systems, to provide a higher charging amperage, simply plugging in a charge-only cable won’t do the trick. The computer has to receive a specific cue that tells it to provide a higher amperage, and that cue is different depending on the device in question.
The USB specification calls for charge-only cables to have the data wires, or terminals two and three, shorted at the device end. So to turn a regular USB cable into a charging cable, terminals two and three on the device end of the cable can be shorted.
This works for most devices, but Apple products do things differently.
Powered USB Ports in Cars
While it is possible for a car to include a power-only port, most USB ports found in cars are still connected to the infotainment system. So even when a vehicle does include a powered port, the primary use of the port will still be to transmit data. The issue here is that in some cases, you may plug your phone in, and the infotainment system will fail to recognize what type of device it is. If that happens, it may fail to charge your phone even if the port is actually capable of doing so.
One way that you can sometimes get around this issue is to use a USB cable that is specifically designed for charging. This type of USB cable is totally incapable of transmitting data, so you won’t be able to use it to transfer files or listen to music. However, the fact that the infotainment system has no way of telling that a device is plugged in means that your phone will receive power from the port anyway.
Another issue with powered USB ports and charging devices like phones is that different companies approach USB charging in different ways. The problem is that while USB ports are all designed to operate at 5v, they are capable of outputting a variety of amperages, and different phones require different amperages to charge. For instance, some phones will charge fine on 1.5A, while others will charge very slowly or even use up more power than is being replenished by the USB charger.
If your car recognizes your phone and connects it in media player mode, via a normal USB cable, there is a chance that the provided charging amperage will not be high enough to maintain the level of charge on your phone.
In any case, you can try using a charging cable that is designed to work with your specific phone, which may do the trick. If it doesn’t, you’re probably stuck with using a cigarette lighter USB adapter.