Right to repair: why some car data is open to everyone and some only to the dealer

A question that eventually occurs to anyone who has noticed the gap between dealer and independent workshops: why does one see everything in the car and the other only part of it?

The answer is not equipment quality but the fact that access to vehicle data is split into two levels, and the boundary was drawn by regulators over thirty years ago.

Two levels of access

Level one: the mandatory minimum

OBD-II appeared as a regulatory requirement for emissions monitoring. Manufacturers were obliged to expose, to anyone with a scanner, the data needed to verify the exhaust after-treatment systems.

What that minimum includes:

• Emissions-related fault codes.
• Live data — RPM, temperature, fuel trims, oxygen sensors.
• Readiness monitors.
• Freeze frames.
• VIN and software identifier — see the Mode 09 guide.

That is the level any ten-dollar adapter reads, and it is precisely why such adapters exist at all.

Level two: everything else

Anything unrelated to emissions is not described by the standard:

• Electric vehicle traction battery condition.
• Transmission data beyond basic codes.
• Module adaptations and individual settings.
• Driver assistance calibration.
• Coding new parts to a specific vehicle.
• Airbag and event recorder data.
• Most body electronics.

The mechanics of that split are in the supported PIDs guide, and what specifically hides behind manufacturer requests is in the Mode 22 guide.

Why this is not a conspiracy

The common view is “manufacturers deliberately lock data to make money on servicing”. There is a grain of truth, but the picture is more complicated.

Manufacturer arguments with substance:

• Safety. Write access to modules means the ability to alter brakes, airbags, and steering. The risks are covered in the cybersecurity article.
• Liability. If third-party equipment ruins a module, the manufacturer ends up dealing with it.
• There is no standard. Manufacturer parameters differ by brand because the designs differ. Nobody attempted to standardise them.

Arguments on the other side:

• The owner bought the car, and data about its condition is their data.
• A monopoly on diagnostics means a monopoly on repair pricing.
• Independent workshops without access cannot service a car fully, leaving owners no choice.

Regulation in various jurisdictions is moving toward wider access for independent workshops — but for a fee and with licensing, not unconditionally.

What this means in practice

For an owner

What you can do yourself: everything in the mandatory minimum. That is more than it sounds — most articles in this blog are built on it. Read codes, check trims, assess condition from live data, inspect a car before buying — see the inspection protocol.

What you cannot: program a new injector, calibrate a camera, assess a traction battery, reset adaptations after a repair.

Practical takeaway: an adapter answers “what is wrong and how serious”. It does not replace a workshop where writing to modules is required.

For an independent workshop

The difference between dealer and independent workshops today is largely a difference in access to manufacturer protocols, not in mechanics’ skill.

Hence the practice: many independent shops buy subscriptions to brand equipment for specific marques. So a workshop specialising in your make is usually a better choice than a generalist.

For electric cars this is critical

The split is felt most sharply here. An electric car’s key parameter — traction battery condition — is entirely outside the standard. Mechanics in OBD on electric cars.

The consequence when buying: battery assessment has to be arranged separately, and without it the deal is blind — see buying a used EV.

Using this sensibly

1. Split the tasks. Diagnosing “what happened” — yourself. Repairs requiring module writes — a workshop.
2. Arrive with data. A code, a freeze frame, and live data change the conversation at the service desk entirely.
3. Verify the result. After a repair, read the codes yourself: gone, or merely cleared. Procedure in the post-repair checklist.
4. Choose a workshop by its brand equipment if the car is complex.
5. Do not attempt to write to modules without understanding the consequences — see warranty and scanners.

In short

• The OBD-II mandatory minimum exists because of emissions regulation, not goodwill.
• Anything not about exhaust is undescribed by the standard — it is the manufacturer’s choice.
• The dealer/independent gap today is mostly access, not competence.
• On electric cars the split bites hardest: the battery is entirely outside the standard.
• An adapter answers “what is wrong”; writing to modules stays with the workshop.

Download the app — everything in the mandatory standard is read with an ELM327 adapter over Bluetooth SPP on Android.