Car Scanner OBD2 ELM: Obd Mary

Review by eFreeware

If a warning light comes on and you want to know what it means before you book anything, this app is built for that moment. Car Scanner OBD2 ELM: Obd Mary, from WyspaTech, turns an Android phone into a diagnostic reader, a gauge panel and a trip logger, provided you have an ELM327 adapter to plug into the car. It is free to install, with ads and in-app purchases, and it has drawn over five million installs and a 4.6 average from a large body of ratings.

The appeal is the combination: fault codes, live engine readings and a dashboard you arrange yourself, all in one place. I would expect it to suit someone who does their own basic maintenance, or who simply dislikes paying a shop to read a code that takes two minutes to retrieve. The adapter requirement is the first thing to weigh, because without one the app has nothing to talk to.

What follows is an assessment of the three jobs the app is built around, the setup it expects, and the kind of owner who will get the most from it.

Reading fault codes and clearing them

The core function is reading and resetting trouble codes from OBD2-compliant control units. When a code appears, you can see a description of it, and a tap takes you to a web search for more context. That last part matters more than it sounds: a code number on its own is rarely enough to decide whether you are looking at a loose gas cap or something that needs a workshop.

Freeze-frame data is available when a diagnostic trouble code has been triggered, which captures the conditions at the moment the fault was recorded. For anyone trying to work out whether a problem shows up when the engine is cold, under load or at idle, that snapshot is often more useful than the code itself.

The app also reads beyond the engine. The developer lists diagnostics for other vehicle control modules, including ABS, SRS, airbag and HVAC, so the scope is wider than a basic code reader. How much of that is reachable depends on the car and the adapter, but the intent is clear: one app covering more than the powertrain.

Live parameters such as speed, RPM, mass air flow and coolant temperature can be watched as the engine runs. Those readings are the difference between knowing a fault exists and understanding what the engine is doing while it happens.

Building a dashboard that suits your car

The dashboard side is where this app asks for some effort and gives something back. You assemble your own set of gauges rather than accepting a fixed layout, and the developer says nearly every visual parameter can be adjusted: sizes, colors, the position of the stroke, arrow, text and labels, plus backgrounds.

In edit mode you resize and move gauges with your fingers until the arrangement looks right. I like the idea of this for a car where the factory instruments are thin on detail, or for a driver who wants coolant temperature and intake readings visible at a glance instead of buried in a menu.

It is worth being realistic about the trade-off. A dashboard you design yourself takes a few minutes of fiddling before it is useful, and that work sits between you and the readings. For a driver who wants a single number and nothing else, the default set of gauges is probably enough; the customization is there for people who enjoy tuning the display as much as reading it.

The recent update added more default gauges and more OBD2 parameters, which suggests the dashboard is being treated as a living part of the app rather than a fixed extra.

Logging trips and fuel costs

The trip computer is the third pillar. With the adapter left connected in the car, the app links to the vehicle and records trip data: trip time, fuel consumption, fuel cost, average speed, maximum speed and similar figures. That turns the app into something you can leave running rather than open only when a light comes on.

The practical setup is a permanently plugged-in adapter. The developer describes a foreground service that maintains the connection with the Bluetooth or Wi-Fi adapter whether the app is in the foreground or the background, and the collected vehicle data is stored locally so statistics such as average fuel rate, average speed, mileage and trip time remain available.

For someone who wants a record of what their driving actually costs, that is a reasonable proposition. It is also the part of the app that depends most on leaving hardware in the car, which not every owner will want to do.

What you need before the first connection

This is not an app you install and use on its own. You need an ELM327 adapter, either Bluetooth or Wi-Fi, to talk to a car. The developer's own quick start is short: install the app, plug the adapter into the 16-pin diagnostic connector, switch on the ignition, pair the adapter in Android's Bluetooth settings, select it inside the app, then connect.

One piece of advice from the developer is worth repeating because it can save a frustrating purchase. ELM adapters sold as version 2.1 are described as often corrupted, and version 1.5 is suggested when you have a choice. If you are buying an adapter specifically for this app, that is the version to look for.

The app also reminds users that a vehicle can contain several electronic control modules, so it is worth checking all of them rather than stopping at the first one that reports clean. Nothing here is difficult, but the sequence has to be followed in order, and the adapter has to be paired before the app can see it.

Coverage across makes and models

The app supports a long catalog of brands, running from Acura, Alfa Romeo and Audi through BMW, Chevrolet, Ford, Honda, Hyundai, Kia, Mazda, Mercedes-Benz, Nissan, Toyota and Volkswagen, and on to less common names such as Lada, Mahindra, Rivian and SsangYong.

A long list is not a guarantee for any individual car, and the honest position is that support depends on the vehicle and the adapter in front of you. What the list does suggest is that the app was not written around a single market or a single manufacturer.

For a household with two or three different makes in the driveway, that matters. It means one app and one adapter can plausibly serve all of them, which is a better proposition than buying a tool tied to one brand.

Drivers who will get the most from it

The clearest fit is an owner who already has an ELM327 adapter, or is willing to buy one, and wants to handle basic diagnostics without a workshop visit. Reading a code, seeing when it was triggered and clearing it afterward is a self-contained job this app covers.

The second fit is a driver who likes data. Someone curious about coolant temperature on a long climb, fuel consumption on a daily route or the real cost of a week's driving will find the dashboard and trip computer worth the setup. That person is also the one most likely to leave the adapter connected and let the app log in the background.

The third is a household covering several vehicles, where the brand coverage and the ability to check more than one control module make a single installation go further. Against that, anyone who wants a polished experience with nothing plugged in will find the hardware requirement an obstacle, and the ads and in-app purchases are part of the free version.

The app has been on Google Play since March 2019 and was updated in September 2026, so it is not a project that was published and forgotten.

A capable diagnostic companion if you own the adapter

Car Scanner OBD2 ELM: Obd Mary reads and clears fault codes with descriptions and freeze-frame data, shows live engine parameters, and logs trips with fuel and speed statistics. The dashboard customization gives it a personality that a plain code reader lacks.

The condition attached to all of it is the ELM327 adapter, plus the version advice that comes with it. If you own one and want to understand what your car is telling you, this is a sensible free starting point, with a full version available for those who want it without ads. If you have no adapter and no intention of buying one, the app has nothing to work with.

For the DIY-minded owner, the data-curious driver, or the household with several cars, I would treat it as a serious option. Install it, pair your adapter, and let the app show you what your vehicle has been keeping to itself.

What's new in version 1.328

Added more default gauges on dashboard Added more OBD-2 parameters Fixed some bugs