Engadget Guides Older Car Audio Upgrades and CarPlay Phone Switching

For wireless music or podcasts, the first step is the connection between phone and stereo. If the car stereo has a 3.5mm AUX input, usually a small round socket labeled AUX or AUX IN, a Bluetooth receiver is likely the simplest upgrade. The phone connects to the receiver over Bluetooth, and the receiver sends sound through the existing AUX input. The original radio and speakers stay in place, and there is no need to take the dashboard apart.

Cars without AUX can use a Bluetooth FM transmitter. These usually plug into the car's 12-volt socket, connect to a phone over Bluetooth and send audio over an unused FM frequency. The car radio is tuned to the same frequency. The drawback is interference: near a radio station using that part of the dial, the user must choose another frequency. Engadget said this is a particular concern for frequent long-distance drivers. AUX avoids that extra FM step, making an AUX Bluetooth receiver simpler when supported.

For maps, calls and messages on a screen, a portable CarPlay or Android Auto display can add a touch screen without replacing the factory radio. These separate screens mount on the dashboard or windshield like a standalone GPS unit. The phone connects to the display, which can show maps, music, calls and messages; depending on the model, audio can play through existing speakers using AUX, FM or another supported connection. Engadget noted that small USB adapters sold for wireless CarPlay or Android Auto cannot add the platform to an older, non-smart radio. A wireless Android Auto adapter only works with a car that already supports wired Android Auto, and wireless CarPlay adapters have the same limitation.

Replacing the factory stereo, often called the head unit, can add a touchscreen, Bluetooth, CarPlay and Android Auto in one built-in system. The catch is that the original stereo may control more than audio. In some cars, it is connected to steering-wheel buttons, the backup camera, a factory amplifier or vehicle settings. Keeping those features working can require vehicle-specific wiring harnesses or interface adapters, so compatibility should be checked before buying a replacement. A professional may be needed to do the swap properly.

Sound quality is a separate issue. If the phone already connects in the desired way but the system sounds weak, distorted or short on bass, Engadget said the better investment is likely speakers, an amplifier or a subwoofer. Better speakers can improve clarity, a compatible amplifier can provide more clean power, and a subwoofer handles deeper bass. There is no single upgrade order that works for every car; the guide recommends starting with the problem the driver can hear or the feature that is missing, rather than replacing components simply because they are older.

The second Engadget guide addresses a common CarPlay situation: multiple iPhones can be paired to the same vehicle, but CarPlay can use only one at a time. If the car automatically connects to the driver's iPhone, no action is needed. If it chooses a passenger's phone instead, the connection must be switched manually. The process varies by manufacturer. Some infotainment systems let users pick a preferred or primary phone under Bluetooth settings or a device management menu, so that phone gets priority when multiple paired iPhones are nearby.

Some manufacturers, including Hyundai, let drivers switch CarPlay or Android Auto connections on the go, and the car should remember the preference the next time it detects the same devices, according to Engadget. As a quick fix, the other iPhone's Bluetooth and Wi-Fi can be turned off manually. A wired CarPlay connection might force the car to prioritize the plugged-in iPhone over a wirelessly connected phone, but Engadget said Reddit users have not had much luck with that method.

For passengers who want to control music rather than take over the whole CarPlay session, SharePlay support for CarPlay, introduced with iOS 17, lets everyone in the car with an iPhone running iOS 17 or newer join the driver's Apple Music session and add, rearrange or remove tracks from their own device. Passengers do not need to be Apple Music subscribers; only the host does. Spotify's Jam feature offers similar functionality and lets everyone in the car join the host's session and contribute from their own phones, with no Spotify Premium requirement in an in-person setting. SharePlay and Spotify Jam only let passengers control music. If they need navigation or messages on the car's infotainment screen, they must manually switch CarPlay connections.