iPhone Duo Touch ID not working is usually down to the finger or the sensor. The phone has no Face ID, and it uses Touch ID built into the side button, which works the same way whether the phone is closed or open.
If you are coming from a Face ID iPhone, you rest a finger on the side button instead of looking at the screen. Work through the fixes in order and test Touch ID after each one.
iPhone Duo Touch ID Not Working Starts With a Clean Side Button and Finger
Moisture, lotions, sweat, oils, cuts and dry skin can all affect recognition, and exercise, showering, swimming and cooking can have a temporary effect. Wash and dry your hands, then wipe the side button with a clean, lint-free cloth.
- Clean and dry your finger and the sensor again before each attempt.
- Cover the sensor fully and keep your finger still through the scan rather than tapping quickly.
- If you use a case or screen protector, make sure it does not block the sensor.
- Open Settings > Touch ID & Passcode and confirm that iPhone Unlock is on and at least one fingerprint is enrolled.
- Enroll a different finger.
- Update to the latest iOS in Settings > General > Software Update.
Your Passcode Is Needed After a Restart and in a Few Other Cases
Touch ID is not what the phone asks for in every situation, so a passcode prompt does not mean the sensor has failed. You need your passcode or Apple Account after a restart, when a fingerprint is not recognized five times in a row, or when you have not unlocked the phone in more than 48 hours.
The phone also asks for the passcode when it receives a remote lock command or when you enroll or delete fingerprints. It asks again when you open Touch ID & Passcode in Settings, use Emergency SOS or view your Medical ID, so if your force restart or a normal restart has just happened, expect the passcode first.
Get Service if Touch ID Is Dimmed or Setup Fails
If the steps above do not help, you may need service, which is also the case if you see “Failed, unable to complete Touch ID setup,” cannot turn on Touch ID or see the Touch ID option dimmed or grayed out.
Technicians handle Touch ID faults with a troubleshooting procedure and a replacement procedure for the Touch ID and camera control buttons, both in the iPhone Duo repair manual. Repairs outside Apple or an Apple Authorized Service Provider are not covered by the warranty or AppleCare plans, so a side button problem is a job for Apple.
