How To Fix an iPhone 13 That Randomly Restarts

Problem description
There are many reasons that could cause an iPhone 13 Mini, iPhone 13, iPhone 13 Pro and iPhone 13 Pro Max to randomly restart every few minutes. For the iPhone 13 series, there are some sensors within the parts of the phone that are required to be plugged in & detected. Otherwise, the phone restarts on its own.

The most common for iPhone 13 series are:


 * Proximity Flex - This is the flex that is attached to the screen. It can easily be liquid damaged or torn during a screen replacement.
 * Charging Port Flex - This is the flex towards the bottom of the phone. It is easily damaged with a drop & the back glass is breaks. Or when someone has repaired the back glass.
 * Board Issue (iPhone 13 Mini Only) - Requires the bottom layer of the 2 layer motherboard.

Symptoms

 * After a back glass repair, the iPhone will restart on its own every few minutes
 * After a screen repair, the iPhone will bootloop every 3 minutes
 * After replacing the charging port flex, the device will auto restart on its own randomly.
 * The iPhone will reboot randomly when using it.
 * The iPhone will seem to freeze and restart every 2-5 minutes.

Diagnostic Steps
Before you start blindly replacing parts, it's important to try to confirm what is causing the restarting issue by reviewing the Panic Log file. This is a file that is generated by the Operating System, to document the fault causing the restart.To find the panic log on the device, go to Settings-> Privacy-> Analytics & Improvements-> Analytics Data-> Scroll down to the files starting with "panic-full..." & click on the most recent dated file. Then you'll want to scan through the text for keywords that may point you to the cause.

For this model, look for where it says "SMC PANIC - ASSERTION FAILED" ... "Sensor Array" .. "0x...."

If you see:


 * 0x1000 - it's the proximity flex cable
 * Check for any liquid damage or torn flex


 * 0x800 - It's the charging port flex
 * Test with known good charging port flex.
 * Check for damaged or missing resistors around the charging port connector

Alternatively, you can use a tool like the iDevice Panic Log Analyzer, which will download the panic logs from the device & display them on the PC & give you suggestions to possible solutions. It makes it easier to browse the panic log file. Also check out www.PanicFull.com which allows you to upload the panic log file & have it analyzed for free.
 * 0x1800 - It's both, the Charging Port Flex AND Prox Flex
 * This means both parts are having issues. You'll need to check both parts are good & not damaged.
 * 0x400 - iPhone 13 Mini only - It's a bottom board issue. The iPhone 13 mini needs to communicate with the gyroscope in order to function correctly and not restart every 3 minutes. Rebuilding pads 207, 208, 502, 503, 504, 527, 528 is all that is needed from the bottom board.

Both of these tools just give suggestions, which aren't always correct, as there is no official solution list from Apple. So many solutions are just suggestions based on hearsay, rumors or just guesses.

For situations where you don't see the above examples, you'll have to read through the top portion of the panic log & try to decipher what could be the root cause. Look for keywords you may recognize.

Repair Steps
When trying to solve for these issues, make sure to replace the appropriate flex with an OEM or Premium flex.

It is also a good idea to keep a known good power button flex & charging port flex in your bench, for testing only. There are reports of even NEW flexes being bad. So you have to keep known good flexes on hand at all times, so you don't waste your time troubleshooting with possibly bad flexes.

In scenarios where you have the appropriate flexes plugged in, but it still restarts, then you either have:

Please note: You MUST have the required flex cables, Power Button & Charging Port, plugged in. Otherwise it WILL restart. You cannot troubleshoot this step by unplugging the bad flex. (This does not apply to the Wi-Fi antenna flex.)
 * Bad or damaged flex
 * Low quality aftermarket flex
 * Other flex cables that are Liquid Damaged