iPhone keeps restarting: how to find the cause

Why does an iPhone keep restarting?

An iPhone restarts by itself when iOS hits a kernel panic: an error the system cannot recover from. Each time, iOS writes a panic-full log and reboots. If the cause is still there after the restart, the panic happens again, and you get a loop.

There are two broad families of causes:

• Software: an iOS bug, a corrupted update, an incompatible app, a jailbreak or a problem carried over by a backup.
• Hardware: a sensor that has stopped answering, a damaged flex, a weak battery, a part that is not recognised, or a fault on the logic board.

The symptom looks the same in both cases. The log is what tells them apart. Without it, the usual approach is to replace parts one after another until the restarts stop, which wastes time and parts, and can even add a new fault if a flex is damaged on the way.

How do I tell software from hardware?

Start by collecting several panic-full files (see How to Get the Panic Full Log From an iPhone) and compare them.

Clue	Leans towards software	Leans towards hardware
Signatures	Different from one log to the next	Same signature every time
Rhythm	Irregular, rare	Regular, often every ~3 minutes
Trigger	After an update, an app install, a restore	After a drop, liquid, a repair
Message	Watchdog on logd, SpringBoard	SMC sensor array, Missing sensor(s), i2c, AOP
After a clean restore	Panics stop	Same panic returns

A clean restore is the decisive test when the log is ambiguous: restore iOS as a new device, without putting the full backup back, and watch for a day. If the panics come back with the same hardware signature, you are looking at a part.

What does the panic full tell me?

The panic string names the family and gives a precise clue: a sensor array code, a missing sensor name, a process name or a bus device. Read How to Read an iPhone Panic Log (Panic Full Guide) for the details, or drop the file into the tool: it returns the likely part for the exact model, the test to run first and the pitfalls.

Which parts cause restart loops most often?

The database groups the signatures by part. These come up again and again.

Charging port flex

The charging port flex carries more than the connector: depending on the model, it also holds the bottom microphone, the barometric pressure sensor and the lines for the loudspeaker or the haptic driver. Signatures: Missing sensor(s): prs0 or mic1, many SMC sensor array codes, some AOP and i2c panics. Aftermarket charging port flexes have a high failure rate: test with a known-good genuine part before concluding.

Battery

When the logic board loses the battery data, the system panics. Signatures: TG0B, TG0V, TB0V missing sensors, or SMC codes such as 0x41 (iPhone 14 Pro), 0xa1 (iPhone 15 / 15 Pro), 0xa9 (iPhone 16 / 16 Pro). A useful check: is the battery percentage shown, or stuck at 0–1 %? A replacement battery shows a "non-genuine battery" warning unless it is an Apple part set up with System Configuration or Repair Assistant (iOS 18+).

Front sensors (proximity, ambient light)

The front flex carries the proximity and ambient light sensors. On recent models it is one of the mandatory sensors the SMC waits for. Replacing it disables True Tone and auto-brightness even with a genuine Apple display, while Face ID has kept working since iOS 15.2.

Wireless charging coil

On iPhones with MagSafe, the coil flex under the back glass carries a sensor the SMC checks. A non-Apple back glass or coil can reproduce exactly the same panic, because the sensor is paired / calibrated to the logic board.

Power button flex

The power button flex can carry a secondary microphone (mic2) and, on some models, a mandatory SMC sensor. It is easily damaged during a back glass replacement.

When is it the logic board?

Some signatures point directly to the board:

• NAND / storage (ANS2, nvme): back up immediately; repair needs micro-soldering and a programmer.
• Secure Enclave (SEP): board link or firmware; device-specific data is involved.
• Sandwich separation: on stacked boards (iPhone 13 mini, 14 Pro, some 16 codes), a gyroscope or interposer fault can produce a sensor array code with no external part to order.
• CPU power or solder joints: some AOP and SMC panics without a sensor array.

Also suspect the board when a known-good part changes nothing, especially after liquid damage: the connector, filters or traces on the sensor's path may be the real fault.

Which software fixes are worth trying first?

When the log points to software, or when you are not sure, these steps come from the documented cases:

• Update iOS through Recovery Mode rather than over the air: it reinstalls the system cleanly.
• Restore as a new device, without restoring the full iCloud or computer backup. In an iFixit case on an iPhone SE 2020 with logd watchdog panics, only a clean restore without the backup stopped the restarts; putting the backup back can bring the problem back.
• Watch the phone for about 24 hours before any hardware work.
• Use a DFU restore for Secure Enclave panics, especially after an iOS downgrade: corrupted firmware is a documented cause.
• Remove any jailbreak or research tool if the log shows a kernel data abort or a memory management panic.

If the same hardware signature survives all of this, stop restoring and move to the part.

What is the right order of work?

1. Back up if the phone stays up long enough.
2. Collect several logs and check that they come from the same device.
3. Read the signature with the model (tool).
4. Rule out software if the signature is a watchdog or the log is ambiguous.
5. Test with a known-good part before ordering: swap the suspect flex temporarily and watch.
6. Confirm the repair: use the phone for a while and check that no new panic-full files appear.

Is it always every 3 minutes?

Not always, but a regular restart roughly every three minutes is a strong hardware signal: it is the SMC's timeout for a missing mandatory sensor. We explain the mechanism in iPhone Restarts Every 3 Minutes: Why and How to Fix. If the phone switches off rather than rebooting, read iPhone Turns Off by Itself? Shutdown or Panic.