EOBD scanners: getting more information from your car

Fri, 24 Jul 2026 12:00:00 +0200

Modern cars are full of sensors monitoring everything from exhaust gas composition to intake air pressure. When something goes wrong, the engine management system logs a fault code and lights the check engine warning. Now, if only cars had screens that could display what exactly is wrong…

No such luck. But it’s easy to get the right tool to read it. That tool is an EOBD scanner.

What EOBD is

EOBD (European On-Board Diagnostics) is the European implementation of the OBD2 standard, mandatory on petrol cars sold in Europe since 2001 and diesel cars since 2004. All cars since then (and some older ones) have a standardised 16-pin diagnostic port, usually under the dashboard on the driver’s side. Every compliant car speaks a common basic protocol. This means one tool can read fault codes from any manufacturer.

The codes themselves are structured: a letter indicating the system (P for powertrain, B for body, C for chassis, U for network communications) followed by four digits. The first digit indicates whether it’s a standard code (0) or a manufacturer-specific code (1 or above). Standard P0xxx codes have the same meaning across all manufacturers - e.g. P0300 means random misfire detected. Manufacturer codes are where it gets less predictable.

The standardised codes cover the basics: emissions systems, engine misfires, sensor faults, fuel system issues. This is what any OBD scanner will read. What standard codes don’t cover: manufacturer-specific features, gearbox details, ABS, airbags, climate control, and other systems outside the emissions-related scope of the EOBD standard.

Self-contained unit vs Bluetooth module

Self-contained scanners are dedicated devices: plug into the OBD port, press read, see the codes on the device’s screen. Some clear codes as well. Basic models cost £20–40 and do exactly this job. They’re easy to use, no need to configure anything on the phone.

Bluetooth modules (or USB, or Wifi) typically using the ELM327 chip or equivalent, pair with a phone or laptop and let an app do the work. They are cheaper, and the app can do much more.

I keep a Bluetooth module in a car all the time. A few times it was useful, once it saved the day. Nice thing is they are powered by the OBD port and have no battery, so they can stay in the car forever.

Budget scanners have varying support for extensions. I got lucky - my very cheap, completely non-brand adapter from a random online seller, just happens to support almost everything I might realistically encounter. But generally, if you want to be sure, check your app’s website for recommended models.

Apps

In pre-smartphone days, I used apps on the laptop (and a USB module instead of Bluetooth). Phone is obviously more convenient and I happily switched to Android apps. I’ve tried a few and my current favourite is Car Scanner. It handles a lot of manufacturer extensions in addition to standard codes, can clear codes, modify settings, and clearly warns which operations are dangerous.

Previously, I used EOBD Facile. I had a paid version (it still costs considerably less than one visit to a mechanic). It’s quite similar, but Car Scanner outperforms it now - it supports many more extensions, and even free version has full features.

Some apps are designed towards engine tuning and focus on performance charts. Torque Pro is a well known example. Not my cup of tea, just mentioning.

For deeper access, manufacturer-specific tools are worth knowing about. I’ve driven several cars over the years and used (or at least researched) a few tools:

Ford: FORScan (free, Windows) with an ELM327 adapter gives very deep access to Ford, Lincoln, and Mazda - these share platforms and FORScan understands all of them. I used it on my Ford Focus many years ago.
Toyota: Toyota Techstream is the official dealer diagnostic software, and it’s available to DIYers via an aftermarket Mini-VCI cable. It reads Toyota-specific codes, performs adaptations (throttle position reset, idle relearn), and covers hybrids including battery health - something generic apps can’t touch. I read about it but I never used it - I had a Toyota, but Car Scanner handled it well enough.
Volvo: VIDA (Vehicle Information and Diagnostics for Aftersales) is the Volvo dealer system. A DiCE interface allows DIY access and is popular in the Volvo enthusiast community. Covers proprietary codes across all systems, not just the powertrain. Worth knowing if you own an older Volvo. I had a Volvo once, but at that time I used EOBD Facile and it worked for my needs.
Kia and Hyundai: these share a platform and generic apps handle them reasonably well for standard codes. Car Scanner has some extended PIDs for Hyundai/Kia that go slightly beyond the standard set.

Getting the code is not getting the answer

A fault code describes what the ECU detected as a symptom, not what caused it. A code saying “misfire on cylinder 2” could be the spark plug, the ignition coil, the high-voltage cable, the fuel injector, a compression problem or a few other things. The code points you at the symptom. The scanner can’t give you diagnosis - it’s giving you a starting point. Sometimes I know what to do next, other times at least I know what to tell the mechanic.

The turbo story

A few years ago, I was driving a Honda Civic with a TDi engine on a mountain road. Suddenly the “check engine” light appeared and the car lost most of its (normally excessive) power. It could barely go uphill, I struggled to get to the nearest safe parking place.

Connected the EOBD module. It showed several error codes - some of them were known to me and expected in an old car. The new ones indicated turbo underboost and overspeed. On a turbo engine, airflow problems could mean several things. The turbine and compressor spin at crazy speeds, are manufactured to incredible precision and can fail in several interesting ways, all of them expensive.

I’m not a mechanic. I opened the bonnet not hoping to achieve much. And immediately discovered an air hose with a cracked connector. I got duct tape. Wrapped it around the hose and the connector to hold it seated. The intention was to get home and at a convenient time replace it properly.

The duct tape held. For 2 years, at which point the car failed for an unrelated reason and was sold for parts. EOBD scanner turned what felt like a serious breakdown into a roadside fix. Without the scanner, the code would have remained unread and the options would have been tow or limp to a garage. With it, the diagnosis took five minutes and the repair took three.

When buying a used car

An EOBD scanner is a useful tool to bring when viewing a used car. Plug it in, read the codes, and see what the car has been logging. Fault codes the seller doesn’t know about - or does know about and hasn’t mentioned - can appear here.

The caveat: the previous owner may also own a scanner. Clearing fault codes before a sale takes thirty seconds. It might leave traces, there might be another more secure location - whether you can find it, depends a lot on your scanner, app and skill. A used car dealer surely has a better scanner and way more experience.

Interestingly, seeing some harmless codes is often more reassuring than seeing none at all. Minor codes - such as a sensor that briefly read out of range - suggest the history hasn’t been cleared. A completely blank fault history on a high-mileage car is slightly suspicious; it’s more likely that codes were cleared than that the car has never logged a single fault. Not a dealbreaker, but worth noting alongside other checks.

What changes with an EV

I’ve never had an EV, but my next car could be electric, so I did a bit of research. EVs still have a standard OBD2, still log fault codes, but the standard PID set that was designed around petrol engines and mostly doesn’t apply. Generic apps will show very little information.

What you actually want to see on an EV - battery state of health, individual cell voltages, pack temperature, capacity remaining, charging system status - is proprietary. For this you need an app that knows the specific extended PIDs for that brand. Since my plans are down to several brands, I researched those.

Kia and Hyundai: Car Scanner has extended PID sets for Hyundai and Kia that cover battery management data. No need to change anything in my current setup.

Nissan: The Leaf has its own dedicated app: Leaf Spy (iOS and Android). It reads the BMS in detail. Works with a standard ELM327 Bluetooth adapter. Leaf Spy is widely used in the Leaf owner community and is effectively the standard tool for assessing used Leaf battery condition. If you’re looking at buying a used Leaf, this is worth knowing about before you go.

Toyota: The Prius has its own dedicated tool: Dr. Prius (free, iOS and Android), which specifically assesses hybrid battery health. For newer Toyota EVs and PHEVs, the Toyota Techstream setup I mentioned above (Mini-VCI cable) covers the full vehicle including the battery management systems. The same cable that works on conventional Toyotas works on hybrid and EV Toyotas.

Diagnostics on Easy-DYI