
Interior modifications can pass the annual inspection as long as they do not affect safe driving. If they impact safe driving, they will not pass the inspection. The annual inspection is something every car owner will encounter, during which professional staff and equipment are responsible for checking the vehicle. According to the relevant provisions of the "Regulations for the Implementation of the Road Traffic Safety Law," motor vehicles must undergo safety technical inspections within the following periods from the date of registration: (1) Passenger vehicles for commercial use must be inspected once a year within the first 5 years; after 5 years, once every 6 months; (2) Trucks and large or medium-sized non-commercial passenger vehicles must be inspected once a year within the first 10 years; after 10 years, once every 6 months; (3) Small and mini non-commercial passenger vehicles must be inspected once every 2 years within the first 6 years; after 6 years, once a year; after 15 years, once every 6 months; (4) Vehicles that exceed the scrapping age cannot be transferred (sold or bought) but can continue to be used.

It depends on which parts are modified. I know many friends who got into trouble with body color changes. If the paint job or wrap exceeds 30% without registration, they'll definitely be turned away at the annual inspection. My neighbor last year applied a matte gray wrap and ended up having to remove it embarrassingly for re-inspection. Lighting modifications are the easiest to get caught—switching to xenon lights without lenses or installing flashing tail lights will be spotted immediately by the police. Hardcore modifications like engine or chassis changes won't pass inspection even with help from intermediaries. I once saw someone on a forum who swapped in a Japanese engine and got it recorded in their vehicle records. The safest bet is to only modify the interior, like adding a car fridge or changing to leather seats—hardly anyone bothers with those.

With twenty years of car repair experience, I've seen countless cases where modifications backfired. The front bumper must perfectly align with the original factory lines—extending beyond the body by more than 5cm will instantly fail inspection. Last time, a carbon fiber spoiler I installed for a client was forcibly removed due to exceeding size limits. Never increase wheel size—forcing 235 tires onto rims designed for 215 width will cause rubbing against the wheel arches during turns. Adding underbody protection plates is fine, but if you raise the suspension to increase ground clearance by 3cm, inspectors will spot it immediately with their measuring tapes. Most crucially, lighting modifications: halogen-to-LED conversions may still pass in some cities if color temperature stays below 6000K and includes projectors—though enforcement varies.

Veterans in the car modification scene all know to keep the OEM parts! Last year at our modding meetup, a Civic owner pulled off a 30-minute full revert to stock for inspection right on the spot. Those with widebody kits usually tow two cars to the testing station—one with stock bumpers for inspection, while the modified beast rides home on the roof. Nowadays, caliper color changes are trendy but fake Brembo decals are a no-go—savvy traffic cops check brake pump serials. Suede headliner mods are fine, but removing rear seats for cargo hauling will get you flagged. Carbon fiber steering wheels? No problem. Tamper with airbags though, and it's illegal. Infotainment mods enjoy the most freedom—massive touchscreens crammed into dashes are fair game.

When I first got my car, I also wondered about the annual inspection. You must be careful with light-colored window films—if the front windshield film has a light transmittance below 70%, it’s like having a sunshade, and the inspection station will spot it immediately with their testing device. Roof racks aren’t something you can just install as you please; those with weak load-bearing structures will be flagged as safety hazards. The worst off are those street-racing kids who modify their exhausts for loud sounds—the Civic in my neighborhood with a modified valve was ordered to revert to stock three times last year. Nowadays, even adding rain guards counts as altering the vehicle’s appearance, and rubber strips that exceed thickness limits can be nitpicked. My advice to beginners: don’t mess with exhausts or lights—just swap in some stylish welcome light strips for a cool effect without breaking any rules.