Car link

Read from the car.

A small Bluetooth adapter plugs into the port under your dash. At the end of each drive Caliper reads the odometer straight from the car, so your mileage matches the dash exactly, along with fuel level on most cars, battery health, check-engine status and engine temperature. While you drive, it logs a full trace at four readings a second — RPM, speed, throttle, and gear on cars that publish it.

Plugging the adapter in isn't enough. You run setup once — sitting in the car with the ignition on, about a minute — and after that every drive reads on its own.

You'll need

A Bluetooth LE (4.0) OBD2 adapter that says ELM327-compatible. The ones we've tested cost about $50 to $80; basic ones start around $25.
An iPhone with Caliper, and Bluetooth on.
A petrol car sold in North America since 2008, or in Europe since 2001. Diesels a few years later.

How it works

Plug it in. The port is under the dash, usually left of the steering column. Push the adapter in until it clicks; a loose plug has power but no data. Then turn the ignition on.
Find the adapter. Settings → Your Garage → Car link. Adapters usually show as OBDII, Veepeak, IOS-Vlink or iCar. If another OBD app is open, close it fully; iPhone shares the Bluetooth link between apps.
Pass the connection test. Three checks, in order: adapter found, car answering, identified your car. Each failure names its cause and what to do about it.
Read at the end of every drive. Once it's connected, Caliper shows what your car shares and takes the first reading. From then on, on Pro, every auto-tracked drive ends with the car's own odometer.

The whole thing takes about a minute. Nothing is written to the car at any point: no coding, no adaptations, no clearing codes. Caliper only ever asks questions.

What to buy

Any Bluetooth LE (4.0) OBD2 adapter that says ELM327-compatible. Everything Caliper sends is the standard command set over Bluetooth LE, so the make of adapter matters much less than the make of car.

The one specification worth reading the box for is whether the adapter sleeps. One that sleeps can live in the port; one that doesn't will draw current for as long as it's plugged in, however little you drive.

Works, but

Veepeak OBDCheck BLE, tested on a 2024 Golf GTI and a 2026 Toyota 4Runner, connects fine, but it has no sleep mode — it stays powered for as long as it's in the port. Fine for a car you drive often; skip it for one that sits.

What to avoid

Bluetooth Classic-only adapters. They pair with Android, not iPhone. If the box doesn't say BLE or 4.0, assume it's one of these.
Wi-Fi adapters. They take over your phone's internet connection while plugged in.
Proprietary tools such as OBDeleven's or Sparq. They speak their own protocol, not ELM327, and only work with their own app.

A wireless CarPlay dongle isn't a Car link adapter: it doesn't plug into the OBD2 port and can't read the car. It's fine to keep using one alongside your adapter, though. They're separate connections, and Caliper uses CarPlay to know a drive has started.

Leaving the adapter plugged in is fine if it sleeps on its own. Caliper only talks to it during a drive — it holds the connection while you're driving and drops it at the end, so it can't keep an adapter awake between trips. An adapter with no sleep mode is a different matter: it draws current for as long as it's in the port, whatever any app does. If yours has no sleep mode, or the car will sit for weeks, unplug it.

What your car shares

Caliper never promises a reading it hasn't seen. The connection test reads what your car actually answers and shows you the list before you commit to anything. In general:

Battery, check engine, engine temperatureStandard. Mandated on every petrol car sold in North America since 1996, and over the modern connection since 2008. Expected to work on essentially any car.

Fuel levelMost cars. Read on every car tested so far, but the fuel-level reading isn't mandated the way the others are, so it isn't guaranteed on every car.

OdometerDepends on the car. The standard reading only arrived in 2019 and is up to the manufacturer, so most cars from 2019 on share it and few before do. Where a make keeps it somewhere else, Caliper has a growing table of make-specific routes, updated without an app release. The GTI, the RAV4 and the 4Runner share it through the standard reading. The 2018 C-Class, built before the standard reading existed, doesn't share it yet. A car that doesn't share its odometer still gets everything else, and Caliper keeps estimating the odometer from trips.

Service countdownVolkswagen group. The car's own oil-change and inspection countdown, to the kilometre and the day, shown beside Caliper's reminder. Confirmed on the Golf GTI; the RAV4 doesn't publish one over OBD, so Toyota and other makes fall back to Caliper's estimate.

Drive playback and fuel economyStandard, where the engine answers quickly enough to sample: RPM, speed and throttle at four readings a second, and gear on cars that publish it. Fuel economy uses the engine's own fuel rate where the car reports it, and says so.

EVs and hybridsMany share little or nothing over the standard connection, and Teslas have no port. You can try; the list will be mostly crosses.

Tested cars

Cars a connection test has been run on, with what each one shared. The list grows from owners who opt in to share their result: make, model and year and the ticks, with no VIN, no location and nothing that identifies them.

Car	Odometer	Fuel level	Battery	Engine temp	Check engine	Service countdown	Drive playback
2024 Volkswagen Golf GTI
2022 Toyota RAV4
2026 Toyota 4Runner
2018 Mercedes-Benz C-Class

read from the car the car doesn't share it not confirmed yet

The two Toyotas don't publish a service countdown over OBD. The C-Class doesn't share its odometer: it predates the standard reading, and the Mercedes-specific route is still being worked out.

If your car isn't here, the connection test is still the honest answer. If a reading you'd expect shows a cross, the failure report in the app sends us what the car said, with the VIN stripped on your phone first, and we'll look into it.

Free and Pro

Setting up the adapter, the connection test and the first reading are free, and that reading stays: the odometer stays confirmed, the service countdown stays on Car Health. Reading at the end of every drive, drive playback, fuel economy per drive, check-engine alerts, the battery trend and fill-up detection are Pro. One Pro, one price; there's no separate adapter tier. Pricing.

Questions?

Email support@calipercar.com. If a car won't connect, say which adapter you have and what the connection test showed.

Tested on a 2024 Volkswagen Golf GTI with an OBDLink CX, a 2022 Toyota RAV4 with a Vgate vLinker MC, a 2026 Toyota 4Runner with a Veepeak OBDCheck BLE, and a 2018 Mercedes-Benz C-Class. Last updated 23 September 2026.