Using an OBD2 scanner takes a few minutes: find the diagnostic port under the dashboard, plug in the scanner, turn the ignition on without starting the engine, and read the stored codes. Every car and light truck sold in the US since the 1996 model year has an OBD2 port, and any OBD2 scanner can read the generic engine codes. Write the codes down before you clear anything.
Where is the OBD2 port?
The 16-pin trapezoid-shaped port is almost always under the dashboard on the driver side, within reach of the steering column, often above the pedals or near the hood release. On a few vehicles it hides behind a small cover in the lower dash or center console.
How to use an OBD2 scanner, step by step
- Turn the vehicle off and plug the scanner into the port; a Bluetooth adapter pairs with a phone app instead.
- Turn the ignition to on (engine off), or start the engine if the scanner instructions say so.
- Let the scanner connect, then choose read codes.
- Note every code and whether it is stored (confirmed) or pending.
- Open freeze frame data for the main code and write down the engine speed, load, coolant temperature and fuel trims.
- Look up each code; our OBD2 codes list explains common codes.
- Diagnose and repair the cause before clearing the codes.
Stored, pending and permanent codes
| Type | Meaning |
|---|---|
| Pending | The computer saw a fault once; it may confirm it on the next drive |
| Stored (confirmed) | The fault was confirmed and usually turned on the check engine light |
| Permanent | Cannot be erased with a scanner; clears itself once the system passes its self-test after the repair |
What is freeze frame data?
Freeze frame is a snapshot of sensor readings at the moment a code set. It tells you whether the fault happened cold or warm, at idle or under load, which narrows the cause. For lean and rich codes, the fuel trims in freeze frame are especially useful; see fuel trim explained.
Live data
Most scanners also show live data: engine speed, coolant temperature, fuel trims, oxygen sensors, MAF and throttle readings. Comparing live data with what you expect is how many faults are found; see O2 sensor, MAF sensor and throttle position sensor.
How to clear codes
After the repair, choose clear codes or erase in the scanner menu. Clearing turns off the check engine light and resets the readiness monitors, which then need normal driving to run again; see drive cycle and readiness monitors and how to reset the check engine light. If the code returns, the cause was not fixed.
Types of scanner
- Basic code reader: reads and clears generic engine codes.
- Bluetooth adapter and app: adds live data and graphs on your phone.
- Enhanced scan tool: reads transmission, ABS and airbag modules and manufacturer codes; some are bidirectional and can command solenoids and run tests. Transmission and ABS faults need this level; see ABS light and P0700.
Shipping is a flat $80.00 per order to US addresses, with 15-day free returns. Questions? Ask a parts specialist.