How to Read an OBD2 Code

What is an OBD2 code?

OBD2 stands for On-Board Diagnostics, second generation. It's been a US-mandated standard since 1996 (and in the EU since 2001). Every modern car has an OBD2 port near the driver's footwell. When a sensor reports a value outside its expected range, the ECU stores a diagnostic trouble code (DTC), a 5-character string like P0420 or P0171, and lights the check engine light. Reading those codes is the first step in any diagnosis.

Step 1. Locate the OBD2 port

The OBD2 port is a 16-pin trapezoidal connector, almost always under the dash on the driver's side within 2 feet of the steering column. Some vehicles hide it behind a small removable panel. If you can't find it, search "[your make] [model] [year] OBD2 port location". Takes 30 seconds.

Step 2. Plug in the OBD2 scanner

Insert the Bluetooth OBD2 adapter into the port. It should click in and fit snugly. Turn the ignition to ACC (accessory) or ON. The engine does not need to be running to read stored codes. Most adapters have a power LED that comes on to confirm the connection.

Step 3. Pair the scanner over Bluetooth

Open your phone's Bluetooth settings. The adapter will appear as OBDII, ELM327, or the brand name (Kiwi 3, BAFX, OBDLink, etc.). Tap to pair. If prompted for a PIN, try 1234 or 0000. Those are the default for almost every ELM327 adapter.

Step 4. Open Trackara and connect

In the Trackara app, open the vehicle profile and tap Diagnostics → Connect Scanner. The app auto-detects the paired adapter and establishes a live connection to the ECU. Takes 2 to 3 seconds.

Step 5. Scan for trouble codes

Tap Scan Codes. Trackara pulls every DTC the ECU has stored, including:

• Stored codes. Confirmed faults that triggered the check engine light.
• Pending codes. Early-warning faults that haven't failed enough drive cycles yet to light the CEL.
• Permanent codes. Codes that can't be cleared until the ECU verifies a real fix.

Each code shows a plain-English description, severity, and most-likely-cause list. So you're not just staring at "P0420".

Step 6. Save findings to the vehicle record

Tap Save Scan. The DTC list, timestamp, and current mileage get written to the vehicle's service history. From there you can generate a task to track the repair, attach photos of the part or damage, and log parts and labor costs as you resolve the issue. Every scan is searchable later when a code comes back.

Step 7. Clear codes after repair (optional)

Once the underlying problem is actually fixed, use Clear Codes. A few honest words of caution:

• Clearing codes before a real fix just resets the check engine light temporarily. The code will return once the ECU runs its readiness monitors again.
• Some states require a completed drive cycle before emissions inspection. Clearing codes the day before a smog test is a bad idea.
• Permanent codes can't be cleared manually. The ECU removes them automatically after verifying the fix over multiple drive cycles.

What do the most common codes mean?

Frequently asked questions