There are many reasons that could cause an iPhone 14 Pro and iPhone 14 Pro Max to randomly restart every few minutes.
For the iPhone 14 Pro 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 14 Pro 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.
Power Button Flex - This is the flex that wraps around the logic board & controls the power button.
2 Layer Sandwich - Requires the bottom layer of the 2 layer motherboard. If the Gyro U7300 is not detected, it will restart. It could have ripped pads on the top board for the Gyro lines.
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.
Solution
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.
An example of panic log files you'll find in the iPhone when it has been randomly restarting.
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:
0x80000 - it's the Proximity Flex Cable
Make sure this flex is plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
0x40000 - It's the Charging Port Flex
Make sure this flex is plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
0x100000 - It's the Power Button Flex
Make sure this flex is plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
0xc0000 - It's the Prox Flex and Charging Port Flex
Make sure both flex cables are plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
0x180000 - It's the Prox Flex and Power Button Flex
Make sure both flex cables are plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
0x140000 - It's the Power Button and Charging Port Flex
Make sure both flex cables are plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
Diode mode the FPC connectors for any faults
0x1c0000 - It's the Charging Port and Power Button Flex and Prox Flex
Make sure all 3 flex cables are plugged in
Check that no flex is torn, liquid damaged, defective
Test with OEM or Premium. Aftermarket Flexes have a high defect rate
iPhone 14 Pro Max will restart when the Gyro is not detected on the top board, giving 0x20000 panic logDiode mode the FPC connectors for any faults
0x20000 - It's a sandwich board issue.
This means the sandwich board has separated. It could require a sandwich reball or a bottom board swap.
Check Gyro U7300
Check the pads for the Gyro U7300: 542, 543, 544, 545, 546, 6, 248
0x41 - It's a battery data issue.
Sometimes you'll see the battery percentage fluctuate or you'll randomly get a "non-genuine" message.
Check the battery connector pins. Sometimes they can bend out & battery won't make good contact.
Diode mode the battery connector pins & compare them to known good board
Test with a known good battery
Replace the battery connector
iPhone 14 Pro Max - This panic log says 0x41, which is related to battery data is missing.Example of what you'll see in a panic-full file, where when there's a bad prox flex and bad charging port flex causing the 3 min restart.
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.
Example of what you'll see in a panic-full file, where when there's a bad prox flex and bad power button flex causing the 3 min restart.
Also check out www.PanicFull.com which allows you to upload the panic log file & have it analyzed for free.
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:
Bad or damaged flex
Low quality aftermarket flex
Other flex cables that are Liquid Damaged
Please note: You MUST have the required flex cables, (Prox flex, Charging port flex, Power Button Flex, Sandwich reballed) plugged in. Otherwise, it WILL restart. You cannot troubleshoot this step by unplugging the bad flex.
