iPhone error 29 is an error that usually occurs when trying to update or restore your device. It may also be a hardware issue that would make the phone non-functional.
Some of the solutions to this error include using the device's original battery, disabling third-party software and updating iTunes.
Please see our in-depth walk-through solutions below.
A problem with the battery may be causing iPhone error 29. If you have changed the original iPhone battery recently, put it back again and start the restore or update again. If the restore or update was successful, you may put the new battery back on. iTunes could have diagnosed you are using a non-Apple product, which leads to the error.
NOTE: Please connect the battery connector properly to avoid additional problems.
iPhone error 29 may also occur when a third-party software (including malware) is interrupting the restoration or the update. Also, it may also show up when your iTunes is not updated. Ensure your iTunes is updated. Please see link here
If you think your operating system infected by malicious software, update, and scan using an anti-virus. After scanning and deleting the malware, configure your operating system to boot without running startup program, please see below.