Steps to Inspect Front & Rear Windshields, Side Windows & Glass Identification Numbers

Inspecting your vehicle’s glass components isn’t just about clear vision; it’s about safety, functionality, and ensuring every pane passes muster. Whether it's your front windshield, rear window, or side glass, knowing what to look for and what those etched codes represent can make all the difference. In this post, we’ll walk through inspection steps in a structured, reader‑friendly way and show how our Pre‑Delivery Inspection (PDI) service ties in to guarantee your vehicle’s glass is flawless.

Start with a Visual Overview

• Front Windshield: Check for chips, cracks, and the condition of the frit (the black border). Look for dot‑matrix patterns that help disperse heat evenly and reduce optical distortion.
• Rear Window: Inspect for defroster wire integrity and any scratches or peeling. Damaged defrosters can compromise visibility.
• Side Windows: Ensure the tempered glass is intact, no cracks, chips, or unauthorised modifications; they’re designed to shatter safely when needed.

Decode the “Bug” (Glass Identification Stamp)

Locate the “monogram” or "bug", usually in the bottom corner of the glass. It’s a goldmine of detail: logos, DOT numbers, AS ratings, E‑codes, M‑numbers, and manufacturing. Break down what each element means:

• DOT Number: Identifies the certified glass
• AS1 / AS2 / AS3: Indicates safety and light-transmission standards, AS1 is typically windshield-grade (highest clarity and safety), AS2/AS3 for side/rear
• Glass Type (Roman Numerals I–V): Indicates glass subtype, like laminated (II), treated multilayer (III), plastic (IV), etc
• M‑Number: Manufacturer’s internal code for glass construction, thickness, colour, etc
• Date Code/Dots: Manufacturing date, often encoded with dots or numbers, for example, dot patterns representing month, year, and day

Inspect Seal, Adhesive & Frit Condition (Windshield Specific)

• Frit Band & Dot-Matrix: This black enamel and dot gradient protects the seal from UV, improves adhesive adhesion, and minimises lensing distortion
• Sealant Inspection: Surrounding urethane should be even, intact, without bubbles or gaps that could let in moisture

Side & Rear Window Safety Features Check

• Tempered Glass Fragments: Ensure edges are chip‑free; damaged tempered glass can shatter dangerously.
• Defroster/Rain Sensor: Test the rear defroster, and for the front, look for the rain sensor lens or film near the rearview mirror if equipped

Cross-Verification with Documentation

Have the car’s paperwork or manufacturer’s spec handy. Match the bug’s information to ensure OEM glass was used, not aftermarket replacements lacking certification

CARS24 Pre-delivery Inspection

CARS24’s Pre‑Delivery Inspection (PDI) service elevates this process: we follow all the steps above (visual checks, bug decoding, seal‑testing, sensor verification), plus we use calibrated tools and inspect under controlled lighting to catch hard-to-see issues. Particularly, we ensure ADAS features reset properly when windshields are installed or replaced, protecting your safety tech.