Water Damage Indicator Check
Check liquid contact indicators (LCI)
Bottom lineLiquid Contact Indicators (LCIs) are small white dots that turn red after liquid exposure; on 2016 and newer MacBooks they sit on the logic board and keyboard panel, visible only with the bottom case off. From outside, shine a light into the ports and look for corrosion, watermark rings, or green/white residue. Any red LCI or corrosion voids the warranty and means intermittent faults are likely—walk away.
Understand LCI
Apple places white indicators inside the Mac that turn red on liquid contact. On modern Macs (2016 and later) they sit on the top case and logic board — not visible without opening the bottom case
Check Headphone Jack (older models)
On some older models (e.g. earlier MacBook Air), a flashlight can reveal an LCI inside the 3.5mm jack — white is normal, red means liquid. Modern models show nothing here
Inspect Ports for Residue
Shine a light into USB-C and other ports, plus the MagSafe port on older models — water rings around the magnetic port are a common leak point. Look for corrosion, mineral rings, or sticky residue
Look for Corrosion Signs
Check port edges, speaker grilles, and vents for white/green residue
How to Open the Bottom Case (if allowed)
Power off and unplug first. Use a Pentalobe (P5) driver to remove the 8–10 bottom screws (note their positions — they differ in length). Lift from the hinge-side edge and tilt the case off. On the logic board and top case, look for small white/red paper dots (2–3 mm) — those are the LCIs. Never force the case or touch the board; if unsure, ask the seller to open it or skip this step
Important: Water damage voids warranty and can cause intermittent issues. Red LCI or corrosion are major red flags. Note: in humid coastal climates, LCIs can very rarely turn red from long-term humidity rather than a real spill — weigh it together with other signs.