Is the cycle always exactly 3 minutes?

No. The timeout is about 180 seconds, but the DFRWS 2025 study measured restart intervals between 50 and 150 seconds depending on the case. What counts is that the cycle is regular.

Can a software update fix a 3-minute restart loop?

Rarely. The sensor is physically silent, so a restore does not bring it back. Restore only if the log shows a watchdog on a software process instead of a sensor array code.

Can I disconnect the part to test it?

Not as a diagnosis: without a mandatory sensor, the phone restarts anyway. Test by swapping in a known-good part instead.

Why did it start right after I replaced a part?

The new part may be badly seated, damaged, or not recognised. Some sensors are paired to the logic board, so a non-Apple part can trigger the same panic.

iPhone restarts every 3 minutes: the missing sensor explained

Updated 2026-10-14

An iPhone that restarts about every 3 minutes almost always has a mandatory sensor that no longer responds. The system management controller waits for it, gives up after roughly 180 seconds and forces a restart. The sensor array code in the panic full log identifies the sensor, and therefore the part, for that exact model.

Why does an iPhone restart every 3 minutes?

The regular rhythm is the clue. On recent iPhones, the system management controller (SMC), built into the SoC, periodically waits for a response from each mandatory sensor: charging port, front sensors, wireless coil, battery data, depending on the model. If one of them stays silent, the SMC gives up after a timeout and forces a restart.

After the restart, the sensor is still silent. The SMC waits again, gives up again, and the iPhone restarts again. That produces a loop with an almost constant period. This regularity is what separates a missing sensor from most software panics, which tend to happen at random moments, for example when a particular app is opened.

The timeout is about 180 seconds, hence "every 3 minutes". In practice the interval varies: the DFRWS APAC 2025 study, which disconnected modules one by one on several iPhones, measured restarts between 50 and 150 seconds depending on the case. A phone that reboots every two minutes like clockwork has the same problem.

What does the log show?

Each restart writes a panic-full file with a signature of this form:

SMC PANIC - ASSERTION FAILED … SMC BSC failure …
sensor array 0 - 4 is 0, 4194304, 0, 0, 0

SMC BSC failure: the SMC did not get a response from a sensor.
sensor array: the list of values; the non-zero one is the code.
4194304: the code, here in decimal. In hexadecimal it is 0x400000.

Each bit of the code is one sensor. If two sensors are missing, two bits add up (0x100000 + 0x200000 = 0x300000). The step-by-step reading is in How to Read an iPhone Panic Log (Panic Full Guide).

On older generations, the same mechanism appears as a watchdog panic with Missing sensor(s): … naming the sensor (prs0, mic1, mic2, TG0B…). The idea is identical: a sensor that should report is missing.

Which part matches which code?

The meaning of a code depends on the model. Examples from the database (single-bit values):

Model	Charging port flex	Front sensors (proximity)	Wireless coil	Battery
iPhone 13 / 13 mini / 13 Pro / 13 Pro Max	`0x800`	`0x1000`	—	`0x4000`
iPhone 14 / 14 Plus	`0x100000`	`0x200000`	`0x400000`	—
iPhone 14 Pro	`0x40000`	`0x80000`	—	`0x41`
iPhone 15 / 15 Plus	`0x80000`	`0x100000`	`0x200000`	`0xa1`
iPhone 15 Pro / Pro Max	`0x100000`	`0x200000`	`0x400000`	`0xa1`
iPhone 16 / 16 Plus	`0x80000`	—	`0x200000`	`0xa9`

On the iPhone 14 Pro, 0x100000 is the power button flex. On the iPhone 13 mini, 0x400 is the gyroscope on the lower board: a logic board sandwich problem, not an external part.

Some codes are disputed: sources give different parts for the same value. For example, 0x500000 on an iPhone 14 is charging port + wireless coil according to the DFRWS disconnection test, but the battery according to iFixit and iPad Rehab. The analyzer shows both readings in that case. The complete list is in the table.

How do I confirm the part?

Get the log between two restarts or from a computer (How to Get the Panic Full Log From an iPhone).
Read the code for the exact model (the product field, e.g. iPhone16,2), or drop the file into the tool.
Inspect the flex and its connector: seating, tears, creases, corrosion, bent pins.
Swap in a known-good part of the same model and watch: if the cycle stops, you have your part.
If a known-good part changes nothing, especially after liquid damage, measure the connector in diode mode: the fault may be on the logic board (connector, filter, trace).

Don't try to diagnose by unplugging the suspect part: without a mandatory sensor, the phone restarts anyway.

What about older iPhones without sensor array codes?

On generations where the log names the missing sensor instead of a code, the cycle has the same cause and the sensor name leads to the part. A few documented cases:

iPhone 11, mic2 missing: the secondary microphone sits on the power button flex. The DFRWS study reproduced the panic by disconnecting the power button. An OL reading at the connector can also come from a separation of the logic board sandwich.
prs0 missing: the barometer is mounted on the charging port flex. On an iPhone 11, a confirmed case was caused by a faulty Taptic Engine, so test it too.
iPhone SE 2020, mic1 missing: the data lines run under the SIM tray and can be cut inside the board. A new flex is not always enough; Repair Wiki describes the bridge to make.
iPhone 12 series, Eiger missing: Repair Wiki links it to the charging port.

Why does part pairing matter?

Several sensors involved in this loop are paired or calibrated to the logic board. A non-genuine part can be perfectly fine electrically and still trigger the panic, or create side effects:

Wireless coil: a non-Apple back glass or coil can reproduce exactly the same panic.
Front sensors flex: replacing it disables True Tone and auto-brightness, even with a genuine Apple display; Face ID has kept working since iOS 15.2.
Battery: a replacement shows a "non-genuine battery" warning unless it is an Apple part.

Use genuine parts set up with System Configuration (Self Service Repair) or, on iOS 18 and later, Repair Assistant, which can re-pair a genuine Apple part (new or used, not reported stolen).

What if there is no sensor array in the log?

If the phone restarts regularly but the log shows a watchdog timeout on a software process (logd, SpringBoard), start with a clean restore. If the restarts are irregular, read iPhone Keeps Restarting? Find the Cause in the Log. If the phone switches off rather than rebooting, see iPhone Turns Off by Itself? Shutdown or Panic.