Three questions get muddled into one here. Does the change belong in the register, does it affect the APK, the Dutch roadworthiness test, and is it legal on the road at all. Those are three different lists, and a modification can sit on one of them and on neither of the others.
The inspection side is set out in the guide to the Dutch APK. What follows is the register side, and what an unregistered change does on the day the car is handed over.
The changes the RDW wants reported
The RDW, the Dutch vehicle authority, publishes its own list of things you tell it about on the page for changing something on your vehicle. It is shorter than most people expect: the weight of the vehicle, the colour, a replaced or repaired odometer, removing the particulate filter data from the register, adjusting the recorded particulate emissions of a diesel, the emission class, and the engine power of a motorcycle.
Above that sits a separate category. Where the construction of the vehicle has been changed in a significant way, the car needs approving again. The Dutch government states that you must have a vehicle approved by the RDW before it is allowed on the road if it is self-built, heavily modified, or never registered in the EU, and that approval is needed if you have made major modifications after receiving the EU registration certificate, which the Dutch calls a wijzigingskeuring, a modification inspection. The RDW’s own guidance to builders names changes to the brakes, the steering or the drivetrain, changes to the seating, and the use of parts that have not been approved.
Everything else is between you, your insurer and the police.
LPG changes a field the inspection reads
A gas installation is the clearest case, because it touches both lists at once.
The fitting goes to an RDW-recognised company, and that company arranges the change in the register for you. The RDW’s page on fitting or removing a gas installation says that if the vehicle is approved the register is amended and an adjusted registration certificate follows within five working days. Do the work yourself and the RDW has to inspect the car afterwards.
The register change then travels. The RDW says it sends the Belastingdienst a message about the fuel change, and the Belastingdienst sends an adjusted road tax (motorrijtuigenbelasting) bill. Fuel type is one of the things road tax is calculated on, so an LPG conversion shows up in what you pay every quarter.
Now the inspection side. Before an APK may be carried out, certain vehicle data have to correspond with the registration register. The RDW’s APK handbook lists the data that must agree with the vehicle, and fuel is on it, with its own code letters: B for petrol, D for diesel, G for LPG, E for electricity, and combinations containing an E for hybrids. A car running on gas while the register says petrol does not match its own entry.
That is why an unregistered conversion is a genuine problem and a tinted window is not. One of them stops a report being issued.
With a towbar, the register records the towing weight
The register does not record that you have fitted a towbar. It records what the car is permitted to tow. The RDW explains that the towing weight is on the back of the registration document at O.1 and O.2, and in the register.
If no towing weight is recorded, or the figure is wrong, you ask the RDW to look at it through its contact form, and it investigates whether the weight can be added. To raise the towing weight, the car goes to the RDW test centre at Lelystad, and it must have a European approved towbar with the correct D-value. Approval produces a new registration card within five working days, with the paper documents and the registration code following separately. The RDW adds one instruction people skip: tell your insurer the adjusted weight.
The APK identity list does mention a coupling, and the detail matters. That requirement applies to a commercial vehicle or bus with a permitted maximum mass above 3,500 kg where no distance to the centre of the coupling is recorded. An ordinary car with a towbar is not failing an identity check because of it.
Tint, wheels and a lowered car
Tinted glass has a hard number on it and no register entry. The APK handbook gives the requirement from article 5.2.42: the light transmittance of the windscreen and the side windows beside the driver’s seat may not be less than 55%. The method is visual inspection, with measurement in case of doubt.
Then read the note underneath it, which is the part that misleads people. The handbook says this requirement is not tested during the periodic inspection for the purposes of issuing an inspection report. A car with illegal front tint can pass its APK. The pass is not permission, and a roadside check is a different conversation.
Wheels have no register field either. The handbook asks that wheels and rims show no fractures, cracks, unsound welding, serious corrosion or serious deformation, that tyres carry no damage exposing the carcass and no bulges, that the main grooves measure at least 1.6 mm around the whole circumference, and that wheels and tyres are properly shielded and stand no more than 30 mm outside that shielding. Wide wheels on a car whose arches do not cover them fail on the last of those.
Lowering sits in the same place. The spring system is an inspection item and is judged on its condition. The height itself is not a register entry. Where the suspension has been altered enough to count as a change to the construction, the modification inspection route above applies.
A remap has a tax consequence most people never hear about
Engine mapping is the one that surprises sellers. The Belastingdienst’s list of the cases in which BPM is payable includes having modified your car so that its CO2 emission is now higher. BPM is the registration tax, normally settled when a vehicle first enters the Dutch register, and a modification that raises the recorded emission can bring it back into play.
For motorcycles there is a separate reportable item, since adjusting the engine power of a motorcycle is on the RDW’s own list of changes to tell it about.
What an unregistered modification does at the handover
It becomes a disagreement about the car, at the worst moment. At our handover the car is checked against what you described, and a conversion or a part that is not on the register and not in your description is exactly the kind of thing that stops a handover dead.
So describe it up front. A towbar and whether the towing weight was adjusted. A gas installation and whether the register says so. Aftermarket wheels. A remap, including one done by a previous owner that you only know about from the paperwork. None of these makes a car unsaleable. All of them make one harder to sell once discovered late.
Pull your own RDW vehicle report and read the entries. If the fuel code, the colour or the weight does not match the car standing outside, you have found a job for before the sale.
We do not want you stripping modifications off to make the car tidier, any more than we want you repairing or valeting it. Tell us what is on the car. Our offer is free, how quickly it comes back depends on how much detail came with the request, and nothing binds you until you accept. If that suits you better than explaining a towbar to private buyers, ask us for an offer.
Frequently asked questions
Which modifications must I report to the RDW?
The RDW’s own list covers the weight, the colour, a replaced or repaired odometer, particulate filter data, the recorded particulate emissions of a diesel, the emission class, and the engine power of a motorcycle. Significant changes to the construction need an approval inspection.
Does fitting a towbar have to be registered?
The towbar is not registered. The towing weight is, at O.1 and O.2. Raising the towing weight requires an inspection at the RDW test centre in Lelystad and a European approved towbar with the correct D-value.
Can a car with an unregistered LPG installation pass an APK?
Fuel is one of the data that must correspond with the register before an inspection can proceed, so a mismatch between the car and its entry is a problem at the inspection itself.
Are tinted windows checked in the APK?
The handbook sets a minimum light transmittance of 55% for the windscreen and the front side windows, and states that the requirement is not tested during the periodic inspection for the purposes of the report. Passing an APK does not make the tint legal.
Do I have to remove modifications before selling?
No. Describe them. The car is checked against your description at the handover, and a surprise found then is far more expensive than a line in an email.