Android Auto keeps disconnecting from USB — fix

Quick answer

Replace the USB cable with a short (1m or less), certified USB-IF cable that supports data and 3A+ power. If that doesn't stick, clean your phone's USB-C port with a toothpick or buy a powered USB hub.

Why this happens

What's actually happening here is your phone's USB controller detects a voltage drop or data signal degradation, then initiates a renegotiation cycle. Android Auto needs a stable 5V at 1.5A-3A to maintain projection mode. Cars don't supply clean, consistent power — the USB port often shares a circuit with the radio, dashboard lights, or even the cigarette lighter. When you hit a bump, turn the AC fan on high, or plug in another accessory, the voltage dips below the phone's threshold. The phone thinks the cable was unplugged, so it drops the connection and tries to reconnect. Rinse and repeat every 2-10 minutes.

Most people blame the phone or the car, but the cable is the weakest link. Cheap or worn cables have higher resistance — you lose 0.3-0.5V just passing through them. That leftover voltage is too low for stable Android Auto. I've seen this exact pattern on Galaxy S23s, Pixel 7s, and OnePlus 11s across Hondas, Toyotas, and aftermarket Kenwood units.

Fix steps (in order of likely success)

Replace the USB cable with a short, certified one. Get a USB-IF certified cable, 1m or shorter. Specs: USB 3.0 or higher, 3A minimum power rating. Anker, Cable Matters, or Belkin all make good ones. The length matters — shorter cable = less resistance = less voltage drop. I keep a 0.5m Cable Matters cable in my car and haven't had a drop in 6 months.
Clean your phone's USB-C port. Pocket lint compacts against the pins and blocks full insertion. Turn the phone off, use a plastic toothpick or SIM eject tool, and gently scrape the bottom of the port. You'll be shocked how much comes out. Re-test with the new cable.
Turn off battery optimization for Android Auto. Go to Settings → Apps → Android Auto → Battery → select 'Unrestricted'. The system can kill the background process when power gets tight. Letting it ignore the battery saver keeps the connection alive.
Disable USB debugging (if enabled). Some phones, especially on developer options, treat the Android Auto handshake differently with debugging on. Turn it off: Settings → Developer options → USB debugging → off. Reboot and reconnect.
Check your car's USB port firmware. Some aftermarket head units (Pioneer, Kenwood) got firmware updates that fixed power stability. Check the manufacturer's support page and update if available.

Alternative fixes if the main ones fail

If steps 1-5 don't work, the problem is likely a weak car USB port. Solutions:

Use a powered USB-A to USB-C adapter. Something like the Plugable USB-C car charger (PD 30W) plugged into your car's 12V socket, then connect your phone to that. The car's USB port is bypassed entirely. Android Auto works over that connection if your head unit supports it (most modern cars do).
Buy a short USB extension cable with a ferrite core. Ferrite cores filter out electrical noise from the car's alternator. I've seen this fix random drops on older BMWs.
Try a different phone. If possible, test with another phone that's known to work in your car. If that phone drops too, the car's port is toast. If it works, your phone's USB-C port might be damaged or have a bent pin. Visit a repair shop for a port replacement.

Prevention tips

Once you get a stable connection, keep it:

Don't use your phone while driving. I know it's tempting, but pulling on the cable while navigating dislodges the connector.
Keep the cable plugged into the car's port when not in use. Constantly plugging/unplugging wears the cable and port.
Buy a spare cable and keep it in the glovebox. When one cable starts to fail, swap it immediately.
Every 3 months, clean your phone's USB-C port. It's preventive maintenance and takes 30 seconds.
If you use a wireless Android Auto adapter like the AAWireless or Motorola MA1, make sure your phone supports 5GHz Wi-Fi. 2.4GHz interference from other devices can cause drops that look like USB issues.

The reason the short cable fix works best is physics — lower resistance and less voltage drop. Don't overthink it. Start with that, and you'll save yourself hours of head-scratching.