Why won't my ELM327 adapter work with my iPhone?

You plug a cheap ELM327 adapter into the car, open a scanner app on your iPhone, and nothing finds it. It's one of the most common problems with these adapters, and it's rarely a fault: the adapter speaks a kind of Bluetooth your iPhone won't let apps use.

Which ELM327 adapters work with an iPhone?

"ELM327" names the job, not the radio. The ELM327 is an interpreter chip that turns standard OBD requests into simple text commands (Elm Electronics), and most cheap adapters copy it. What links the adapter to your phone is a separate radio, and there are three kinds:

The cheapest adapters are usually classic Bluetooth, which is why so many people hit this wall.

Why a classic Bluetooth ELM327 doesn't show up in iPhone apps

Android lets an app open a classic-Bluetooth serial connection to almost any device. Apple doesn't. Its developer note QA1657 explains that the framework iPhone apps use for classic accessories "is designed to allow iOS applications to communicate only with hardware accessories that are developed under Apple's MFi licensee program," and an app "will not be notified of an accessory's presence unless the accessory identifies itself as being MFi compliant."

So a no-name classic adapter may even pair in Settings, and the scanner app still can't see it. No app update fixes that; it's the platform.

The same note gives the way around it: "Bluetooth low energy accessories do not interface with the External Accessory framework and are not required to be MFi compliant. Instead, apps use the CoreBluetooth framework." That's why BLE adapters work.

A few classic-Bluetooth adapters do work on iPhone because their makers support iOS officially. OBDLink, for example, lists iOS among the supported platforms for its MX+ (OBDLink). If an adapter's maker doesn't name iPhone support, assume it has none.

Is my ELM327 classic Bluetooth, BLE or Wi-Fi?

• Read the box or listing. BLE adapters usually say "BLE", "Bluetooth 4.0" or "Low Energy", and often "for iOS". "Bluetooth" alone, or a pairing PIN such as 1234 or 0000, usually means classic.
• Ignore the version number. "v1.5" and "v2.1" on cheap adapters are the ELM327 firmware version the adapter claims to be, not its radio (our inference). The BLE adapter we test with reports itself as "ELM327 v1.5", and it works well: from Chrome on a computer, it read a test car's VIN and logged a drive with no Bluetooth drops (measured).
• Look in the app, not in Settings. A BLE adapter often doesn't appear under Settings › Bluetooth, and doesn't need to. The app scans for it and connects directly.

BLE ELM327 still not connecting to your iPhone?

1. Turn the ignition on. Most cars won't answer until the ignition is on; Elm's data sheet suggests ignition on, engine off, for a first test.
2. Check the app's Bluetooth permission in iPhone Settings, under Privacy & Security › Bluetooth.
3. Close other OBD apps, on your phone and on any other phone in the car. A BLE adapter generally serves one connection at a time, and another app that grabbed it first will keep it (our inference).
4. Unplug the adapter for ten seconds and plug it back in to reset it.
5. Make sure the app supports BLE adapters. Some iPhone scanner apps only support Wi-Fi or their own hardware.

If the adapter connects but the car doesn't answer, the problem is between the adapter and the car, not the phone. See why an OBD2 scanner won't connect to the car.

Does a Wi-Fi ELM327 work with iPhone?

Wi-Fi ELM327 adapters create their own small Wi-Fi network, and your phone joins it. They work with iPhone apps that support Wi-Fi adapters. The catch (our inference from how they connect): while the phone is on the adapter's network, it isn't on your home or other Wi-Fi, so anything that needs the internet falls back to cellular data. For an app that sends data to the cloud while you drive, BLE is the more comfortable choice.

Can a web OBD2 app work on iPhone?

Some scanner apps run in the browser and reach the adapter through Web Bluetooth, which only talks to BLE devices. Chrome on Android and on computers supports it; Safari on iPhone and iPad doesn't, and Can I use tracks whether that changes. On an iPhone, in practice, a scanner has to be an app from the App Store or a beta channel.