ELM327 adapter not connecting: checklist

1. Make sure the 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.

2. Check the port and the ignition

The OBD2 connector (officially the Data Link Connector, or DLC) is generally under the dashboard on the driver's side, near the steering column. EPA guidance treats the area under the driver's side of the instrument panel as the preferred location and allows a few other locations, so on some models it sits behind a small cover, a panel or in the center console.

Push the adapter fully into the connector and switch the ignition on. Many adapters show a light when they have power. Some cars need the engine running before the engine computer answers.

3. Use the right connection type

• Bluetooth Classic: pair the adapter in your phone's Bluetooth settings first, then connect from the Bluetooth tab in OBD Master Pro.
• Bluetooth LE: do not pair it in phone settings. Connect from the BLE tab in the app.
• Wi-Fi: connect your phone to the adapter's Wi-Fi network, then connect from the app.
• USB OTG: use an OTG cable or adapter that your phone supports.

4. Check protocol support

OBD2 cars use one of five protocols, and cars sold in the US from the 2008 model year use CAN. Genuine ELM327 chips support all five OBD2 protocols. The ELM329 is a CAN only version, so an ELM329 class adapter will not talk to an older car that uses J1850, ISO 9141-2 or KWP2000.

You normally do not need to choose a protocol. The adapter and the app detect it automatically.

5. Consider the adapter itself

Many low cost adapters sold as ELM327 are clones of the chip, and quality varies. Many cheap clones only handle engine OBD2 and drop out on modules such as ABS or airbag. If the adapter connects for engine codes but not other modules, the adapter is the likely limit.

6. Send a connection log

If it still fails, open Connection in OBD Master Pro, try to connect, then use Share connection log and email it to support. The log shows where the connection stopped, which is the fastest way to find the cause.

Keep reading

Related guides: Check engine light on: what to do · How to read an OBD2 code · Stored, pending and permanent codes · OBD2 readiness monitors explained · How to clear the check engine light · What is fuel trim · OBD2 live data and PIDs · OBD2 port pinout · What is a U code? · OBD2 glossary

Common codes: P0171 System Too Lean · P0420 Catalyst Efficiency · P0300 Random Misfire · P0455 EVAP Large Leak

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