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 fuel level, battery and check-engine status from the car itself, and on most cars from 2019 on, the odometer too, so your mileage and service reminders match the dash exactly.

You'll need

A Bluetooth LE (4.0) OBD2 adapter that says ELM327-compatible. Around $25 to $50.
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.

Tested

Veepeak OBDCheck BLE, the reference adapter and the one Caliper is developed against. Inexpensive and reliable, but it has no sleep mode — its own maker says to unplug it if the car will sit for more than a week.

Also recommended

Not run against a car by us yet. They're here because they meet what Caliper needs: Bluetooth LE, ELM327-compatible, and a sleep mode.

Vgate iCar Pro 2S, Bluetooth 5.2, and the one to buy rather than the older iCar Pro BLE 4.0. Sleeps on its own after about fifteen idle minutes, down to a few milliamps, and wakes when an app connects.
OBDLink CX, the premium option. Sleeps on its own, with the lowest draw of any of these.

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 is fine. It's a different device on a different link, and Caliper uses the CarPlay connection alongside the adapter.

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:

Fuel level, battery, engine temperature, check engineStandard. 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.

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. 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. Other makes fall back to Caliper's estimate.

Drive playback and fuel economyStandard, where the engine answers quickly enough to sample. 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.

2024 Volkswagen Golf GTI Odometer Fuel level Battery Check engine Service countdown Drive playback

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 a Veepeak OBDCheck BLE. Last updated 18 September 2026.