Bluetooth OBD2 Scanner

What you need

One thing: a Bluetooth Low Energy OBD-II adapter. That qualifier is the whole game, and it is where nearly everyone gets stuck.

• Bluetooth LE adapter — works. Sometimes labelled BLE, Bluetooth 4.0, or “works with iPhone and Android”. You will not pair it in your phone or computer’s Bluetooth settings; you pick it from the browser’s own chooser when you press connect.
• Bluetooth Classic adapter — cannot work. This is the very common cheap blue ELM327 that you pair in system settings. It speaks a serial profile that browsers have no access to, on any platform. Nothing on this page can reach it.
• Wi-Fi adapter — cannot work. A web page cannot open a raw network socket to the adapter’s IP address.
• USB adapter — not supported here. A wired adapter uses a different browser capability (Web Serial) that this page does not implement.

Your vehicle needs to be OBD-II compliant, which means essentially every car and light truck sold in the US from 1996 onward. Turn the ignition to the run position — dash lights on. The engine does not need to be running, but the key does need to be on, or the adapter will connect happily and then report no data from the car.

How to use it

1. Plug the adapter into the OBD-II port. It is under the dash on the driver’s side, within reach of the driver’s seat — if you cannot find it, the port location and pinout guide covers where it hides on each make.
2. Turn the ignition on. Dash lights up. Engine running is fine too.
3. Press Connect to adapter and pick your dongle from the list your browser shows.
4. The scanner sets the adapter up, detects your vehicle’s protocol, and reads all three code types. It takes a few seconds — protocol detection on the first request is the slow part.
5. Tap any code for the full diagnosis, common causes, and what the repair usually runs.

Stored, pending and permanent — the difference matters

Most scanners show you one list and leave you to guess. The three modes answer genuinely different questions, and reading them together tells you more than any one of them alone.

A pending code is a fault the ECU has seen once and has not confirmed. Most monitors need the fault to appear on two consecutive drive cycles before the light comes on, so a pending code is your early warning: something is starting to go, and the dash has not caught up. If you have a rough-running car and no light, this is the list to look at.

A stored code is confirmed. This is what turns the check engine light on and what a shop reads.

A permanent code is the one people do not know about, and it is worth being precise about it, because the internet is not. The regulation says permanent codes are stored in non-volatile memory and “may not be erasable by any scan tool command (generic or enhanced) or by disconnecting power to the on-board computer.” That last clause is the part that surprises people: the old battery-disconnect trick does not touch these either. It is deliberate. The whole reason permanent codes exist is to stop someone clearing codes in the parking lot to slide through an emissions test.

Only the vehicle removes a permanent code, and only after the relevant monitor has actually re-run and found the fault genuinely gone. So if you clear your codes and a permanent code stays behind, your adapter is not broken and neither is your car — that is exactly what is supposed to happen. The requirement was phased in across the fleet: half of 2010 model year vehicles, three quarters of 2011, and all 2012 and later. An older car returning nothing here is normal, not a failed read.

About clearing codes

The clear button is here because leaving it out just sends you somewhere with fewer warnings attached. But it is worth being blunt about what it costs.

Clearing erases the freeze frame: engine speed, load, coolant temperature, fuel trim and more, captured at the instant the fault set. For an intermittent problem that is frequently the most valuable evidence in the car, and once it is gone you wait for the fault to happen again to get it back.

Clearing also resets every readiness monitor to not-ready. Those monitors are the self-tests the car has to complete before an emissions test will even be accepted, and they only run under specific conditions — certain speeds, temperatures, fuel levels, sometimes a cold start. Depending on the vehicle and the monitor that can take anywhere from a short drive to several days of ordinary driving. Clearing codes the morning of a smog check is a reliable way to fail it. Our readiness monitor guide covers what each one needs.

And clearing does not fix anything. If the fault is still there, the code comes back — usually within a drive cycle or two.

If it will not connect

• The dongle is not in the chooser list. Nine times in ten it is a Bluetooth Classic adapter, which no browser can reach. If it is genuinely a BLE adapter, unplug it for ten seconds and plug it back in — many stop advertising once something else has connected, and a phone that auto-connects in the background will hold it hostage. Turn Bluetooth off on any other device nearby that has used it.
• On Android, nothing appears at all. Chrome needs Location permission to scan for Bluetooth devices, and Location itself has to be switched on system-wide. This is an Android requirement, not something the page asks for.
• It connects, then says no response from the vehicle. The ignition is almost certainly off, or only in accessory. Turn the key to run.
• It connects and the adapter answers, but the car does not. Check the adapter is fully seated — the connector needs a firm push. If it is seated and the port is dead, the OBD port has its own fuse on most vehicles; the port tester walks through checking for power on pin 16 and the 60-ohm CAN reading across pins 6 and 14.
• Codes read but come back garbled or partial. Cheap ELM327 clones vary enormously in firmware quality. Open the adapter log above — if the raw responses look truncated or full of question marks, that is the dongle, not the car.

Common questions

Your data stays on your device

The Bluetooth connection is made by your browser directly to the adapter. Codes are decoded here in the page. No vehicle data, no VIN, and no scan results are sent to this site or to anyone else, and nothing is stored between visits. The one network request a scan makes is for our public code index, which is the same file the search box on this site downloads — it is what lets each code show its description without a page load. It is a plain download; it carries nothing about your car with it. Open your browser’s network tab during a scan if you would rather see that than take our word for it.