Many iPhone users encounter random restarts and often wonder what causes this issue. After an iPhone boots up normally, its operating system continuously monitors internal components and connected peripheral accessories. If the system detects a faulty component on the main logic board or a missing peripheral device, it will trigger an automatic restart.
Once the device reboots, it generates restart logs named panic-full or panic-base in the system — these are the well-known crash reports. Note that no such logs will be created if the iPhone fails to complete a full normal boot. These logs record core system crash data and error codes, which serve as critical references for technicians to diagnose faults during repairs.
Here is how to locate these logs on your iPhone:

  1. Open Settings
  2. Tap Privacy & Security
  3. Select Analytics & Improvements
  4. Find and open the files starting with panic-full or panic-base.
  6. As shown in the picture, this is the restart log file. It contains the exact date and time of the reboot, which occurred at 08:03:20 on January 1, 1997.
  7. Do you know how to read these restart reports after opening them
  9. After opening the file, you only need to check the content following panicstring. When troubleshooting iPhones with random restarts, compare the timestamps across multiple logs to determine if the reboots happen at regular intervals (e.g., every three minutes) or intermittently. Combined with the analysis details in the logs, you can quickly narrow down and pinpoint the faulty area for most restart-related issues.
    Here is how to interpret the logs: Locate the line labeled panicstring. It indicates the reboot type, as well as problematic components, circuits or peripherals. You can analyze the root cause via the corresponding error codes.
    These reboot logs can be divided into two main categories. The first type directly names the faulty component or accessory. The second does not specify a part but provides directional clues. Below are examples of reboots with clearly stated faulty components:
    You will see explicit error codes such as apcie2 (wlan), which means the restart is caused by the Wi-Fi module.

  10. Audio (Restart caused by audio module issues)
    For logs with indicative error codes, the devices usually show obvious functional faults. For instance, the phone restarts when turning on Wi-Fi, connecting a charger or playing audio. It may also reboot immediately when using certain features. Such restarts generally occur irregularly when you check the timestamps in the logs.

    Indirect fault description types are as follows:
    These error codes are commonly seen on systems running iOS 18 and earlier. Typical examples include useprspace watchdog timeout (WDT, watchdog timer timeout) and missingsensor (sensor missing), as well as Prs0, a code marking localized system crashes.
    For faults without clear indications, you can narrow down the problematic area based on these crash codes. For certain iPhone models, Prs0 points to the barometric sensor or vibration motor on the bottom flex cable. Most devices with such logs restart regularly roughly every three minutes.
    Among all codes, PCIELLCI2C is easy to identify. These represent buses and data transmission lines connected to the CPU, including PCIe lines for Wi-Fi, baseband and storage chips. Abnormal PCIe data transmission will trigger device restarts, which are usually flagged directly with the PCIe-related error codes.
    LLC and I2C are common bus types. They connect the CPU to functional chips responsible for Wi-Fi, audio, charging accessory detection and other modules, as well as external components like microphones, barometric sensors and compasses.
    LLC is also associated with the CPU cache. That explains why replacing the cache chip can fix LLC-related restarts on certain iPhones. Such faults usually come with obvious symptoms: partial function failures, or error prompts indicating incomplete installation packages when installing apps from third-party platforms. LLC-triggered restarts are irregular, and the corresponding crash logs vary greatly.
    The I2C bus links numerous external components. On specific iPhone models and iOS versions, abnormalities on this bus will lead to periodic restarts. The system constantly checks the connectivity of peripherals such as microphones, compasses and barometers.
    In actual repairs, you can search for terms like I2C2 with suffixes on circuit schematics to quickly locate circuits and narrow down the scope for testing.
    Apart from the above two types, restarts most frequently seen on iPhones are related to AOPPNIC, SMCPNIC, SEPPNIC, WDT and DCPPNIC. To diagnose these issues, you need to combine indicative codes and prefixes from the restart logs.
    For example, the error AOPPNIC-no pulse points to malfunctions in the audio circuit, and vibration-related faults are the most common cause. Generally, AOP errors indicate abnormal analog output.
    When encountering such restarts, analyze the logs alongside the device's actual symptoms to narrow down the faulty area. These error codes correspond to specific hardware circuits. You need to refer to circuit schematics and conduct troubleshooting based on real faults. Taking AOP as an example, search for I2C lines in the schematics to locate the relevant circuit and make further judgments.
    If the log shows DCPPNIC-DISPLAY, the fault is related to the screen. DCP indicates abnormal DC power supply. This issue often occurs after installing an aftermarket screen, or results from defects in the original screen, display IC and other associated components, such as unstable display power output or short circuits. To troubleshoot this type of restart, combine the device's actual performance and directional error codes in the logs to identify and narrow down the faulty area.
    Restarts caused by SMC and WDT are among the most common types in iPhone crash logs. SMC refers to the System Management Controller, while WDT stands for Watchdog Timer malfunction.
    You can look up most SMC-related error codes on circuit schematics in much the same way you search for I2C bus issues. Due to variations across iPhone models and iOS versions, error codes differ accordingly, so practical repair experience is essential for accurate diagnosis.
    On iOS 18 and later, SMC codes have largely replaced traditional WDT entries. In most cases, SMC-triggered restarts are linked to faulty external accessories, with the device rebooting approximately every three minutes. The suffixes of these codes vary from model to model.

    To sum up: On iOS 18 and earlier versions, frequent restarts are triggered by WDT (useprspace watchdog timeout). On newer iOS versions, SMC-related restarts prevail. Both issues generally stem from communication failures between the CPU and external components.