iPhone — Fault Diagnosis

iPhone Fault Diagnosis: Why It Won’t Charge, Won’t Turn On, or Drains Too Fast

Your iPhone isn’t working properly. Maybe the screen is cracked. Maybe the battery drains by lunchtime. Maybe it won’t charge at all — you plug it in and nothing happens. Maybe it won’t turn on, or it turns on and immediately restarts. Or maybe the camera has stopped focusing, the speaker sounds muffled, or the microphone has stopped working on calls.

iPhones are among the most reliable phones ever made, but they have specific fault patterns that differ from Android devices — and the repair economics are different too. Apple’s out-of-warranty pricing is high, some components are paired to the logic board in ways that limit independent repair options, and the diagnostic tools Apple provides are different from anything on Android. Knowing exactly what’s wrong matters more on iPhone than on most devices, because the gap between a cheap fix and an uneconomical one is wide.

This guide covers the faults iPhone owners actually experience across the iPhone X, XR, XS, 11, 12, 13, 14, and 15 series. For each fault, it explains the symptoms, the likely cause, how to test it, what the repair costs, and whether the repair makes financial sense. Some faults are genuinely DIY-able — force restarts, cleaning a charging port, checking battery health. Others require screen or battery replacement, and the guide is honest about when the repair cost approaches the value of the phone.

Common iPhone Problems

  • Screen cracked — glass damage versus OLED panel damage

  • Screen has green or pink lines — the known iPhone OLED display fault

  • Battery drains fast — degraded cell, rogue background app, or a specific system fault

  • Battery Health showing “Service” — Apple’s own diagnostic warning

  • iPhone won’t charge — port debris, cable fault, or charging IC failure

  • Charges slowly — non-certified cable, faulty charger, or degraded battery

  • iPhone won’t turn on — drained battery, force restart failure, or hardware fault

  • Stuck on the Apple logo — boot loop or failed update

  • Charging port loose or intermittent — worn Lightning or USB-C port

  • Camera blurry or not focusing — lens debris or failed camera module

  • Speaker crackling or no sound — debris, water damage, or speaker failure

  • Microphone not working on calls — port blockage or hardware fault

  • Face ID not working — TrueDepth camera fault or software issue

  • Wi-Fi or Bluetooth won’t connect — software fault or antenna issue

  • iPhone overheating — during charging, gaming, or light use

  • Battery swollen — screen lifting away from the chassis

iPhone-Specific Fault Patterns and Known Weak Points

Different iPhone generations have different weak points, and knowing yours matters for both diagnosis and repair cost:

  • iPhone X, XR, XS — the display cable faults that cause green or pink lines. The iPhone X in particular has a well-documented OLED panel fault that appears as a vertical green line on the right side of the screen. Also common: battery degradation after four years.

  • iPhone 11 series — very reliable overall. Battery health degrades noticeably from year three. Charging port faults from lint compaction.

  • iPhone 12 series — the iPhone 12 and 12 Pro had a documented issue with the earpiece speaker during calls. Battery degradation is common.

  • iPhone 13 series — highly reliable. Screen replacement costs are high because of the ProMotion display on Pro models. Battery replacement is the most common service item.

  • iPhone 14 series — the iPhone 14 and 14 Plus use a removable back glass design that makes rear glass repair significantly cheaper than on earlier models.

  • iPhone 15 series — USB-C replaced Lightning, so charging port faults present differently. The port is more durable but can still accumulate debris.

  • All models — battery health degradation, screen damage, and charging port faults are the three most common service items across every generation.

  • Models with swollen batteries — a battery that has expanded physically presses the screen away from the chassis. This is a safety issue. Do not charge a swollen iPhone, do not press on the screen, and store it away from flammable materials until it can be assessed.

What You’ll Learn About Apple’s Own Diagnostic Tools

Most iPhone owners never find the built-in diagnostics, and they’re genuinely useful:

Force Restart — the fastest fix for most “won’t turn on” and frozen-screen faults. The procedure varies by iPhone model. On iPhone 8 and later, press Volume Up, then Volume Down, then hold the side button until the Apple logo appears.

Battery Health Check — Settings > Battery > Battery Health & Charging. This shows maximum capacity and peak performance capability. A maximum capacity below 80% means the battery has reached the end of its service life. A “Service Battery” message means the battery needs replacement.

Recovery Mode — connects the iPhone to a computer with Finder or iTunes to repair software faults, reinstall iOS, or restore from backup. This resolves most boot loops and failed updates.

DFU Mode — a deeper recovery mode that restores the iPhone when Recovery Mode doesn’t work. The guide explains the procedure for each iPhone generation.

Apple Diagnostics — available through Apple’s online diagnostic service or by appointment at an Apple Store. Reports specific fault codes pointing to the failed component.

The guide explains how to run each of these, how to interpret the results, and how to use them to narrow the fault before you pay anyone.

Major Diagnostic Areas Covered

  • Screen damage assessment — how to distinguish glass-only cracks from OLED panel damage, and why the distinction changes the repair cost completely

  • Green and pink line diagnosis — the known OLED display faults that affect several iPhone generations, and whether they’re repairable or a bin decision

  • Battery health and drain diagnosis — how to read the Battery Health report, how to identify a rogue background app, and how to recognise a swollen battery

  • Charging port and cable testing — cleaning Lightning and USB-C ports safely, checking for bent pins, and testing for correct charging current

  • Won’t turn on fault finding — force restart procedures, Recovery Mode, DFU Mode, and the charging-before-diagnosis rule

  • Camera and speaker issues — cleaning techniques, hardware testing, and module replacement options

  • Microphone and Face ID faults — port cleaning, software resets, and understanding the TrueDepth camera limitation

  • Wi-Fi and Bluetooth faults — software resets, antenna checks, and when the fault is hardware

  • Overheating diagnosis — distinguishing normal thermal behaviour from a genuine fault

  • Repair cost reference — typical parts and labour costs for every iPhone fault, with Apple’s out-of-warranty pricing as the baseline

  • Repair-versus-replace framework — with thresholds adjusted for each iPhone model and current resale value

What the Complete Guide Covers

This is a full diagnostic reference covering the iPhone X, XR, XS, 11, 12, 13, 14, and 15 series, with the same structure as our other device guides:

  • A complete guide to Apple’s built-in diagnostic tools and when to use each

  • Step-by-step testing procedures for the battery, charging system, and charging port

  • Force restart, Recovery Mode, and DFU Mode procedures for every iPhone generation

  • Battery health assessment and the swollen battery identification procedure

  • Screen damage assessment and the OLED versus LCD cost difference

  • Green and pink line diagnosis and when it means the panel has failed

  • Full repair cost reference table with Apple’s out-of-warranty pricing

  • Repair-versus-replace framework with worked examples across all iPhone model ranges

  • Model-specific notes covering the differences between generations

What You’ll Learn

You’ll learn how to run the force restart procedure for your specific iPhone model — which is genuinely different depending on whether you have a Home button or not. That single fix resolves a surprising proportion of “won’t turn on” and frozen-screen complaints.

You’ll learn how to clean a charging port safely and how to test whether your cable and charger are delivering enough current. You’ll learn how to read the Battery Health report and what a maximum capacity of 78% actually means for performance and daily runtime.

You’ll learn how to recognise a swollen battery and what to do about it — including why you should never charge a swollen iPhone. You’ll learn how to assess screen damage and understand why a cracked screen on an iPhone 14 Pro costs three times as much to repair as a cracked screen on an iPhone XR.

You’ll learn how to run Recovery Mode and DFU Mode through a computer to fix boot loops and failed updates. And you’ll learn how to check whether a green line on your screen is a repairable display cable fault or a terminal OLED panel failure.

And you’ll learn the threshold that matters most: when a $50 battery replacement or a $150 screen repair is obviously worth doing, and when an out-of-warranty logic board fault on an older iPhone means replacement is the only sensible option.

Repair or Bin?

iPhone repair economics vary enormously between models.

iPhone X, XR, XS — worth $100 to $250 used. Battery replacement at $50 to $90 is worth doing. Screen replacement at $120 to $250 is borderline. Logic board or Face ID faults usually mean replacement.

iPhone 11 and 12 series — worth $180 to $400 used. Battery replacement at $60 to $100 is worth doing. Screen replacement at $150 to $300 is worth doing on most models.

iPhone 13, 14, 15 series — worth $300 to $900+ used. Almost any repair short of a logic board fault is worth doing. Battery and screen replacements are clearly justified.

  • Battery replacement — $50 to $120 depending on model and whether it’s Apple or independent. Worth doing on any iPhone under five years old.

  • Screen replacement (LCD/XR/11) — $100 to $200. Worth doing on almost any iPhone.

  • Screen replacement (OLED/ProMotion) — $200 to $400. Worth doing on iPhone 12 and newer, borderline on iPhone X and XS.

  • Charging port repair — $60 to $120. Worth doing on any iPhone under five years old.

  • Camera module replacement — $60 to $150. Worth doing on most models.

  • Speaker replacement — $50 to $120. Worth doing on any iPhone under five years old.

  • Face ID repair — rarely economical. Face ID components are paired to the logic board, and replacement usually requires Apple service or a specialist. Often a bin decision.

  • Logic board fault — $200 to $400+. Usually a bin decision on older models, borderline on newer Pro models.

  • Swollen battery — replace the battery promptly. Never continue using or charging a swollen iPhone.

The guide gives you the exact threshold for each fault, with worked examples across the iPhone range.

Frequently Asked Questions

Why won’t my iPhone charge?

Check the cable and charger first, then clean the charging port with a wooden toothpick to remove lint and debris. If charging still fails, the port or the charging IC may have failed. The guide covers the diagnostic sequence.

Why won’t my iPhone turn on?

Try a force restart first — press Volume Up, then Volume Down, then hold the side button until the Apple logo appears. If that doesn’t work, connect it to a computer and try Recovery Mode. If the iPhone still shows no response, the battery or logic board may have failed.

Why is my iPhone battery draining so fast?

Open Settings > Battery and check which apps are using the most power. If no single app stands out, check Battery Health in Settings > Battery > Battery Health & Charging. A maximum capacity below 80% means the battery has reached the end of its service life.

Why does my iPhone screen have a green line?

This is a known OLED display fault that affects several iPhone generations, most commonly the iPhone X and iPhone XS. Depending on the cause, it can be a repairable display cable fault or a terminal panel failure. The guide explains how to tell the difference.

Is it worth repairing an iPhone?

Usually yes for batteries, screens, and charging ports on iPhones under five years old. The exceptions are Face ID faults and logic board faults, where the repair cost often exceeds the value of the phone.

Get the Complete iPhone Fault Diagnosis Guide

Stop guessing whether your iPhone is finished. This guide covers every common fault, walks through Apple’s own diagnostic tools, and gives you the repair-or-replace answer for your model.

iPhone Fault Diagnosis Guide — $7.95

Know the fault. Fix it properly. Or know when it’s time for a new one.

Related Guides

iPad Fault Diagnosis Guide — $7.95
The iPad equivalent. Covers screen damage, battery health, charging faults, and won’t-turn-on diagnosis with the same Apple-specific procedures.

Samsung Galaxy Fault Diagnosis Guide — $7.95
The Android equivalent. Covers screen damage, battery drain, charging faults, and software issues with Samsung-specific diagnostic tools.

Google Pixel Fault Diagnosis Guide — $7.95
The Google equivalent. Covers the Tensor chip thermal issues, screen damage, and charging faults with Pixel-specific procedures.

MacBook Fault Diagnosis Guide — $7.95
The Apple laptop guide. Completes the Apple ecosystem coverage if you own a MacBook alongside your iPhone.

Bluetooth Speaker Won’t Charge — $7.95
Same lithium-ion battery and charging circuit diagnostic principles applied to a different device. Useful if you’re working on multiple charging faults.

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