Can an OBD2 scanner damage my car?
Reading codes and live data with an OBD2 scanner is a normal diagnostic use of the port and does not change how the car runs. The real risks come from leaving untrusted or wireless devices plugged in while driving, clearing codes at the wrong time and changing module settings without a backup.
Key facts
| Key fact | Detail |
|---|---|
| Reading codes and live data | Data requests through the standard diagnostic port |
| Commands that change things | Clearing codes (service $04) and, where supported, component tests or coding |
| Leaving it plugged in | Some carmakers, for example Ford, warn against aftermarket plug-in devices during normal driving |
| Security | FBI and NHTSA advise not to connect unknown or untrusted devices to the OBD-II port |
| Clearing codes | Resets readiness monitors and erases freeze frame |
| Good practice | Read first, save data, unplug when done |
Reading data is what the port is for
The OBD2 port is the standardized diagnostic connector that technicians and inspection stations use to check vehicle systems and emissions. Most of what a scanner does is request data: current values, freeze frame, stored and pending codes and vehicle information. These requests do not change settings.
A few OBD functions do change things. Clearing codes erases stored codes and the freeze frame and resets readiness. Brand functions such as coding, adaptations and actuator tests write to or operate modules, so use them only when you know what they do.
The real risks
- Leaving a device plugged in while driving. Ford's owner's manuals warn not to connect wireless plug-in devices to the data link connector and say aftermarket devices used during normal driving may interfere with or damage vehicle systems.
- Untrusted devices. The FBI and NHTSA warn that third party devices connected to the diagnostic port could introduce security vulnerabilities, and advise not connecting unknown or untrusted devices.
- Clearing codes at the wrong time. Clearing before a repair loses the freeze frame, and clearing before an inspection leaves monitors not ready.
- Coding without a backup. Changing module settings can change how features behave. Make a backup first so you can restore the original coding.
How to use an adapter safely
- Buy an adapter from a seller you trust and keep its firmware and the app up to date.
- Plug it in, switch the ignition on, read and save codes and freeze frame before clearing anything.
- Do not use the phone while driving. Park safely before looking at data.
- Unplug the adapter when you are done rather than leaving it connected.
- Before coding, read the current settings, back them up and change one thing at a time.
OBD Master Pro and safety
OBD Master Pro reads codes, freeze frame and live data, and offers clearing, coding and service resets where supported. It includes coding backup and restore so you can return to the original settings. Results depend on your car, its modules and your adapter.
Try it on your own car
OBD Master Pro turns your Android phone and a generic ELM327 adapter into a code reader: read and clear codes, view freeze frame and live data, and check emissions readiness.
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 · ELM327 adapter not connecting · 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
All OBD2 guides · OBD2 by car brand · OBD2 trouble code guides
Sources
- FBI and NHTSA public service announcement I-031716-PSA: Motor vehicles increasingly vulnerable to remote exploits (2016)
- Ford Owner's Manual: Introduction, Special Notices (On Board Diagnostics Data Link Connector)
- Ford Owner's Manual (another model variant): Introduction, Special Notices
- Wikipedia: OBD-II PIDs (SAE J1979 services and standard parameter IDs)
- U.S. Code of Federal Regulations, 40 CFR 86.1806-05, On-board diagnostics (govinfo.gov)
- U.S. EPA: Performing Onboard Diagnostic System Checks as Part of a Vehicle Inspection and Maintenance Program (EPA420-R-01-015)
- California Bureau of Automotive Repair: On-Board Diagnostic Test Reference
- OBD Master Pro on Google Play (app features, supported connections and protocols)
Published . Updated . General information only. Details generally vary by model, year and market, so always follow the owner's manual and service information for your vehicle.