How to choose an ELM327 adapter

What is an ELM327 adapter?

ELM327 is an OBD interpreter chip from Elm Electronics. It translates the car's OBD2 protocols into simple commands that an app can use, and all versions of it support the standard OBD2 protocols. Many low-cost adapters sold as "ELM327" are clones of the chip, and their quality varies.

OBD2 itself allows five protocols: SAE J1850 PWM, SAE J1850 VPW, ISO 9141-2, ISO 14230-4 (KWP2000) and ISO 15765-4 (CAN). Cars sold in the US from the 2008 model year must use CAN, and most modern cars use it.

Step 1: check that your car has OBD2

In the United States, OBD II has been required on all 1996 and newer gasoline passenger cars and light trucks, and on 1997 and newer diesel passenger cars and light trucks. A small number of 1994 and 1995 gasoline models already had it. On US models you can confirm it by looking for "OBD II" on the emission control label under the hood.

In the European Union the equivalent system is called EOBD. For petrol passenger cars (up to 2,500 kg) it applied to new type approvals from 1 January 2000 and to all newly registered cars from 1 January 2001. For diesel passenger cars (up to six seats and 2,500 kg) the dates were 1 January 2003 for new types and 1 January 2004 for all new registrations. Heavier passenger cars and vans followed on later dates.

These dates are the legal minimum for new vehicles in each market. Some cars had OBD earlier, and imported or grey market cars follow the rules of the market they were built for, so the exact start year may vary by model.

Step 2: pick a connection type that suits your phone

OBD Master Pro on Android connects to ELM327 and ELM329 class adapters in four ways:

• Bluetooth Classic: pair the adapter in your phone's Bluetooth settings, then connect from the Bluetooth tab in the app.
• Bluetooth LE: no pairing needed, connect from the BLE tab in the app.
• Wi-Fi: your phone connects to the adapter over Wi-Fi.
• USB OTG: a cable adapter connected through your phone's USB port.

The iOS version of OBD Master Pro is coming soon. If you plan to switch to iPhone later, check that the adapter you choose also supports iPhone.

Step 3: decide what you need to read

Generic OBD2 is built around emission-related systems: engine trouble codes, readiness monitors, freeze frame and live engine data. For that, a basic ELM327 adapter is generally enough.

Modules such as ABS, airbags or body electronics are outside the generic standard. OBD Master Pro can scan them on supported cars through brand profiles, but many cheap ELM327 clones only handle engine OBD2 and drop out on ABS or airbag. For multi-module diagnostics and coding, use a genuine ELM327 class adapter.

Quick checklist before you buy

• Your car has OBD2 or EOBD (see the dates above).
• The adapter states support for all OBD2 protocols, including CAN.
• The connection type works with your phone (Bluetooth Classic, Bluetooth LE, Wi-Fi or USB OTG).
• If you need more than engine codes, the seller states multi-module support, not only basic OBD2.
• You can return it if it does not connect to your car.

Using the adapter safely

• Plug it into the OBD2 port, switch the ignition on and connect from the app.
• Unplug it when you are done. Some carmakers, for example Ford in its owner's manuals, warn against leaving aftermarket plug-in devices connected during normal driving.
• If the adapter will not connect, OBD Master Pro can share a connection log with support from the Connection screen.

Keep reading

All OBD2 guides · OBD2 by car brand · OBD2 trouble code guides