Vehicle Body Systems
Structure, restraint, and repair integrity
Body questions blend structure, joining methods, and safety systems. Distinguish cosmetic outer panels from structural members: rockers, aprons, rails, and pillars carry crash energy and must be repaired per OEM procedures, including sectioning locations, weld counts, and adhesive use. High-strength and ultra-high-strength steels often cannot be heated or conventionally repaired, and heat-affected zones must be respected.
Know the joining methods: GMAW (MIG) for steel, squeeze-type resistance spot welding that mimics factory welds, rivet bonding with structural adhesive, and squeeze rivets or self-piercing rivets on aluminum. Adhesives need correct surface prep and cure time. After welding or sectioning, restore corrosion protection - primer, seam sealer, and cavity wax - because bare welds and heat-affected zones corrode first. Panel fit is measured as gap and flush, typically in the 4–6 mm range with flush within about 1 mm and consistent side to side.
Safety systems are examinable. SRS components include airbags, seat belt pretensioners, occupant sensors, and the clock spring. Disconnect the battery and wait the OEM-published time before working near SRS, never probe yellow connectors with a test light, and follow scan tool procedures after replacement. Hybrid and electric vehicles add high-voltage cables and batteries that must be de-energized before body work. Glass is bonded with urethane, which needs proper bead profile and safe drive-away time.
Traps: treating a structural member as cosmetic; skipping corrosion protection after a weld; probing an airbag circuit.
Worked example: using a gap gauge, a door shows 7 mm gap at the front and 4 mm at the rear - adjust hinges to equalize near the OEM spec before touching the latch.