What your car knows about you: telematics, counters, and module data

A modern car keeps records about itself continuously — and some of those records are about the driver rather than the car. Understanding what is stored is useful for two reasons: it affects selling the car and any investigation of an incident.

What the modules store

Fault counters — codes, cycle counts, freeze frames with conditions; covered in the freeze frame article.

Over-rev counters — some cars store the number of over-revs broken down by band. That is what a dealer looks at in a warranty dispute.

Engine hours and start counts — where the manufacturer keeps them.

Regeneration statistics on a diesel.

Transmission and engine adaptations — they describe how the car was used.

Mileage in several modules at once — which is exactly why odometer fraud shows up as a mismatch; covered in the odometer fraud article.

The event data recorder

A separate category: a module logging parameters around an airbag deployment — speed, pedal positions, belts, steering angle in the seconds before impact.

This is not “surveillance” in the everyday sense: the recording is short and tied to an event. But for an investigation it is decisive; the detail is in the EDR article.

Telematics and connected services

On modern cars with a built-in connectivity module the picture is wider.

What can be transmitted: location, mileage, system status, driving style, service notifications.

To whom: the manufacturer, the dealer, and with consent an insurer; insurance telematics is covered in its own article.

A practical question when buying used: the previous owner may have left their account linked to the car. Then they can see its location and may retain access to functions. Unlinking the account is a mandatory step at handover.

The same when selling: delete your account, saved addresses, the phonebook in the infotainment, and Bluetooth pairings.

What OBD actually shows

Worth separating clearly.

The diagnostic connector gives access to codes, live parameters, and some service counters. That is what any scanner sees, including yours.

What it does not give: a “trip history” in the everyday sense — routes, places, times. Those live in the telematics module and infotainment, not in the diagnostic protocol.

In practice: a buyer with an adapter sees the technical history — codes, monitors, counters — not the personal one.

What to do when selling

1. Unlink the manufacturer account from the VIN.
2. Reset the infotainment to factory settings.
3. Delete Bluetooth pairings and saved navigation addresses.
4. Remove your home address from favourites.
5. Take the memory card out of the dash cam.
6. Do not clear the diagnostic codes — that is a different thing, and it shows; covered in the clearing codes article.

In short

• Modules store mileage in several places — which is how fraud is detected.
• Over-rev counters exist and are used in warranty disputes.
• An EDR records the seconds around a deployment, not continuously.
• Unlink the previous owner’s account when buying used.
• OBD gives technical history, not routes and locations.

Download the app — codes, counters, and live parameters are read with an ELM327 adapter over Bluetooth SPP on Android.