If your iPhone is shutting down or rebooting unexpectedly, chances are there is documentation of this issue in your phone. Diving into your logs seems like a daunting task. But if you know what to look for, it can provide invaluable data about the nature of the problem.
This page is by no means a complete list. If your panic isn't listed, post in the answers forum! Someone else is bound to have experienced the same thing.
What Is a Panic?
In terms of macOS, iOS and other Unix based Operating Systems, a kernel panic is an error the operating system encounters that it cannot, or cannot readily recover from. In many ways, it is comparable to a Windows Blue Screen of Death. It manifests as an unexpected shutdown, or reboot.
If your phone is rebooting unexpectedly, there is a very good chance it's a kernel panic. You just didn't know that's what it's called.
In iOS devices, kernel panics nearly always indicate a hardware issue.
How to Find a Panic Log
iPhones store system logs in a menu seldom tread by the average user—deep in the caverns of the analytics settings.
- Open the Settings app.
- Navigate to Privacy
- Scroll to the bottom and open “Analytics & Improvements”
- NOTE: The exact verbiage of this menu name will depend on the version of iOS your phone is running.
- Open Analytics Data.
- Scroll through the alphabetically presented list to the “P” section and skim for any entries with the word panic in the title. Usually they are listed as panic.full, followed by the date and time the panic occurred.
Reading a Panic Log
There is an abundance of extraneous information in these logs. Skim through the first bit to find the panic string. This is the error that ultimately led to the crash. This error may also be listed without the panic string verbiage immediately following the CPU caller (this simply means which bit of the CPU reported the issue). There may even be helpful data beyond that in the first screen or so of text.
- Use your brain. You may encounter terms found elsewhere in electronics. For example, WLAN is often used to reference Wi-Fi. Issues with your WiFi chip, or antenna, is a logical conclusion if you see WLAN in a panic log.
- You may find things in the log which refer to specific logic board components. Names like Tristar, Tigris, Chestnut, and many others can give clues.
- Ultimately, if you see data which looks like it's not just a string of meaningless letters and numbers, do some research. You'll be surprised at what you can learn from these logs, even if you're not a software engineer.
- Bear in mind that reading panic logs is not an exact science. There is no absolute cause and effect. The same panic string could have five different solutions. A panic log is a clue, and nothing more.
Types of Panics
Watchdog Timeout Thermalmonitord Missing Sensor
Included in its system processes, iOS contains a regular check of sensor input. If it does not hear from these sensors within three minutes, it reboots the phone. Jessa at iPad Rehab has done a rather extensive write up on this specific issue.
To get to cause, keep reading past the panic string to find the missing sensor.
- PRS0 and Mic1 are generally part of the charge port flex.
- Mic2 is in the power button flex in most models.
- TG0V and TG0B are a function of the battery. For the 11 Pro and Pro Max, these may also point to a bad charge port flex due to the second connector on these batteries.
- Other sensors are less well documented, and may require some context since Apple does not publicize locations or names of sensors. iPads appear to have some vital sensors on the display. Board level sensors also exist, but suffer from the same guesswork at nomenclature.
Watchdog Timeout No Check In
The Watchdog Timeout process checks for overall functionality of the system. If the amount of time between check ins exceeds the maximum (typically 180 seconds), the device reboots to attempt to correct this.
- Rather than a missing sensor as previously discussed, you may also get a check in failure from a software component. Springboard, logd, wifid or thermalmonitord (with no reference to a missing sensor) are common. Although these processes may correlate to a hardware component, this is typically a software issue.
- This issue has cropped up commonly in early versions of iOS 16. The solution is generally to ensure you have a backup and restore your phone's software.
- It remains to be seen whether Apple has corrected this with iOS 16.2, but attempting to update is worth a go if you don't want to backup. Try using the Recovery Mode method to process the install to avoid reboots mid process.
i2c or i²c, if you want to be technically correct, is an electronics based protocol used for communication between a net of chips. This includes a master and any number of minions it sends commands to.
I won't get too into the weeds on how this works, but in many cases, the master chip is the CPU. As you can imagine, if the CPU does not get information it needs, or commands it sends aren't received, bad stuff happens.
This particular panic will need lots of context. iPhones contain several different i2c "channels" and which components talk on which channel varies by model.
- The panic may include some other clues. Part names like ALS for Ambient Light Sensor or others may appear in the verbiage.
- Having access to the schematic will make deciphering this panic much easier since it will tell you which components communicate on which channels. It may also give you addresses for the problematic chip.
AOP panics are a whole subset of panic types. AOP is the Always On Processor, a segment of the CPU that runs functions that are always on. Always On functions can run even when the device is off. Recent updates to the Find My network allowing the device to continue transmitting its location in an off state, likely make use of this tech.
AOP NMI POWER
An NMI is a "Non-Maskable Interrupt." In plain terms it's information which cannot be ignored and can interrupt the transmission of other signals. It is usually intended to be used for some sort of error, or system resets.
- This panic is often affiliated with the power button cable, or the front facing camera assembly.
AOP Panic - K2 - Bosch control channel write failure
This panic typically occurs during audio related functions, like turning up the volume to maximum.
- Because the charge port flex assembly carries signals from the speaker to the board, damage to this assembly is the most common cause for this panic.
- Check for liquid damage to be certain and replace with a high quality, or OEM replacement if possible.
ANS2 Recoverable Panic
ANS2 (Apple NAND Storage version 2) is Apple’s controller for, you guessed it, storage. NAND is a type of flash memory commonly used in modern smartphones and computers with soldered on storage.
- If you get this panic, chances are the chip which houses all the data on your phone is malfunctioning or communication lines to the NAND are not functioning properly.
- Replacing the NAND requires microsoldering skills and the use of a programmer to write unique data from the old NAND chip to the new one.
AppleSocHot: Hot Hot Hot
Sometimes software developers have more fun coding in what occurs in times of error than other things because they are likely to be the only ones that see them. This error is pretty straight forward. Your CPU is not just hot—it's Hot Hot Hot.
- This specific panic refers to an electrical line between the Power Management chip and the CPU. It could in fact mean your CPU is getting too hot. It could also mean, a board level issue with this line.
- Regardless of the specifics, this is almost certainly a logic board issue, not a parts problem.
SEP ROM Boot Panic
The Secure Enclave Processor or SEP is the part of an iPhone subsystem which handles all protected, sensitive data for an iPhone. Things like encryption keys and fingerprint or facial identification data. The Read-only Memory or SEP ROM is an integral part of this system which verifies trust between systems.
- A SEP ROM panic indicates the ROM chip or the communication between it and the CPU is damaged.
- The data on the SEP ROM is unique so if it is damaged, it cannot be recreated. There are readers which may allow you to pull the data off, but it can spell disaster for the phone.
SMC Panic Assertion Failed
The SMC, or System Management controller will be familiar to those who have ever done any sort of troubleshooting on a MacBook. iPhones also include an SMC, but rather than being its own chip, it is part of the CPU. These panics often make mention of the error BSC FAILURE.
- Assertion Failed type panics have begun cropping up in iPhone 13. Similar to a Watchdog Timeout, they reboot the device at the three minute mark
- The log will generally mention an affected sensor array followed by a code.
- 0x800 is on the charge port assembly.
- 0x1000 is part of the front facing sensor cable.
- 0x4000 is part of the battery.
- These codes reference sensors in the iPhone 13 series, and does not necessarily reflect the same parts in future series.
Undefined Kernel Instruction
This kernel of an Operating System is exactly what it sounds like—the core parts. If Instructions are undefined, often this is because the instructions are damaged or not functioning properly.
- Generally this is a software issue. Check for OS updates, or even app updates.
- If updates do not resolve, you may need to reinstall or restore the operating system altogether.
- If the issue continues to occur beyond this, you’re most likely looking at an issue with system involved in RAM or the NAND storage. This is where instructions tend to be located and when those components, or their board related systems are damaged, so can the information they’re housing or transmitting.