B3 Collision — Non-Structural Repair — practice test

High-yield B3 topics

The material that shows up year after year. If you're short on time, start here.

• Substrate ID and heat limits. Know the difference between mild steel, HSS, martensitic, boron, and aluminum, and what each allows: cold straightening only on most HSS, a heat cap around 1200 F where the OEM even permits heat, and no heat and no straightening on boron/UHSS - those come out at factory seams or at an OEM-specified section joint. Expect at least one item where the correct answer is "look it up in the body repair manual," not "heat and pull."
• GMA plug welds and destructive testing. Typical 8 mm plug hole, weld count equal to or greater than factory in the factory locations, and a test coupon burned in the same position and same thickness before you touch the car. A passing destructive test tears the nugget out of the base metal - if the joint peels apart clean, that is cold lap, not penetration. Know burn-through versus cold lap symptoms and when the OEM calls for STRSW instead.
• Body filler chemistry and limits. 1/8 inch max thickness, applied per the TDS - bare metal or properly sanded epoxy, never over etch primer or lacquer primer. Cream hardener is roughly a 2 percent mix: fold it in, do not whip it, or you build in the pinholes you will chase later. Too much hardener gives staining, bleed-through, and pinholes; too little never fully cures and keeps shrinking. On aluminum, use a filler formulated for aluminum - standard polyester over aluminum invites galvanic corrosion.
• Hammer, dolly, and shrinking. On-dolly hammering stretches metal; off-dolly is how you bring highs down and lows up. Read the damage in reverse order - the last dent in is the first one out - and release the ridges before you chase the center. For stretched crown, know the shrinking hammer and the stud-welder shrink tip, and know that heat shrinking is off the table on aluminum and on high-strength steels.
• Movable glass and hardware. Regulator and run-channel diagnosis (binding glass versus a failed cable regulator), express-down/pinch-protection relearn after a battery disconnect or regulator R and I, and the defogger grid voltage test: about 12 V at the feed, roughly 6 V at the midpoint of a good grid line, 0 V at the ground side. Also know that side glass is often laminated now, not tempered, and that door-mounted impact sensors get handled and torqued per spec.
• Corrosion protection and panel fit. Epoxy primer on bare metal, weld-through primer on mating flanges only, seam sealer replicated to match the OEM bead shape and location, cavity wax in enclosed sections, and foam restoration where the factory foam was cut. On adjustment, gaps and flush are typically nominal in the 3-5 mm range - and the striker is adjusted last, after hinges and gap, never used to force a gap that the hinges should have set.

Where techs lose points on B3

Good technicians miss these — not from lack of skill, but because the question is built to catch them.

• The magnet test. A magnet tells you ferrous or not - it does not separate mild steel from HSS, martensitic, or boron. Any answer that identifies steel grade by magnet, spark, or "it looks like a normal fender" is wrong. The only right answer is the OEM body repair manual or the vehicle-specific sectioning info.
• On-dolly versus off-dolly. Hammering directly on the dolly stretches and thins the metal - that is the trap answer dressed up as "working the dent out." Off-dolly is what knocks the high down and pulls the low up. Same family of trap: pulling from the center of the dent instead of releasing the ridges first (last in, first out).
• "More welds is better." Match or exceed the factory weld count per the OEM, but do not convert intermittent welds to a continuous bead, and do not add welds outside the specified locations. Extra heat and extra welds where the OEM did not put them is a wrong answer even though it feels like extra quality.
• Weld-through primer as corrosion protection. It goes on mating flanges only, at the joint, and it is not a substitute for epoxy primer, seam sealer, or cavity wax on the finished repair. If a Tech A/Tech B item has one tech calling weld-through primer good enough on the exterior surface, that tech is wrong.

A study plan that works for B3

Roughly two weeks of real preparation, in the order that actually builds on itself.

1. Days 1-4: Metal first. Learn to name the substrate before the repair - mild, HSS, martensitic/boron, aluminum - and what each one allows: cold straighten only, heat limit, or replace at factory seams. Pull up any free OEM body repair manual (Honda and Toyota post theirs) and read one real sectioning procedure end to end. That single habit answers a third of the test.
2. Days 5-8: Welding and cutting. Burn plug welds in 18-gauge coupons in flat, vertical, and overhead, then destructive-test every one with a twist tool - if the nugget does not tear out, your settings are wrong, not the coupon. Practice spot-weld removal that keeps the underlying flange intact. Review weld-through primer placement, STRSW vs GMA, and rivet-bond/SPR rules.
3. Days 9-12: Filler and metal finishing. Work a real dent: ridges first, off-dolly for the highs, only then map the lows. Then mix filler by the TDS - fold, do not whip - and hold it to 1/8 inch. Read the tech data sheet for the filler on your own shelf and note the approved substrates. Add movable glass here: regulator R and I, express-down relearn, defogger grid voltage test.
4. Days 13-14: Practice questions only, and grade the misses by task area. Anything you got right by feel instead of by rule, go back and find the rule. Skim corrosion protection, seam sealer bead shape, cavity wax, foam restoration, and gap/flush adjustment order the night before - those are cheap points people leave on the table.

Sample B3 questions

Straight from the bank — answers highlighted, with the explanation underneath.