BMW E91 enthusiasts listen up: How do you find the ultimate diagnostic tool for your E91?


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As a proud E91BMW 3 Series owner, you certainly want to get the most out of your vehicle, whether it’s by tracking down problems, optimizing performance, or customizing certain features. Don’t worry, you don’t have to rush to the nearest repair shop every time a check engine light flashes. The solution lies in the purchase of a BMW E91 diagnostic device that will make you your own vehicle doctor. In this article, we will help you find the best diagnostic device for your BMW E91.

Which is the right BMW E91 diagnostic device for your car? There is a wide range of equipment suitable for your BMW E91, and therefore the cost may vary. For example, you can find a simple scanner for as little as 30 euros that will allow you to read fault codes. However, there are also professional devices with a variety of functions that cost thousands of euros. A great and inexpensive option is the Carly app and scanner. The Carly app costs between €21 and €80 per year, and the Carly Universal OBD Scanner costs €59.90 (one-time purchase).

In this article, we’ll give you a deeper insight and show you what to look for when buying a diagnostic device for your BMW E91.

Everything you should know about BMW E91 diagnostic tools

Before we recommend you a BMW E91 diagnostic tool, let’s clarify the basics so that you understand the components of vehicle diagnostics.

Types of diagnostic equipment

To perform vehicle diagnostics, you need the appropriate diagnostic device. There are three different types on the market: external standalone diagnostic devices, laptop software and smartphone apps. Each of these variants has its advantages and disadvantages. From our point of view, the smartphone app is the best solution, as it offers many advantages that far outweigh the few disadvantages.

External diagnostic devices usually have a small screen and are suitable for simple diagnostics. Unless, of course, you opt for an expensive piece of workshop equipment that costs thousands of euros – but in doing so, you sacrifice mobility. Portable external diagnostic devices can be inexpensive, but offer limited features and small screens that only display fault codes. You then have to do a lot of research to find out what the codes mean. Plus, you always have to take the device with you when you travel, which means extra hassle.

Laptop software is rather impractical for the average driver or car enthusiast, since you have to take your laptop and the appropriate adapter cable with you. In addition, the software is chargeable and may not be updated regularly. If you do, you will probably have to pay for the update, which will increase the total cost over time. However, laptop software provides comprehensive diagnostic solutions, and the computer’s large screen can display a lot of data.

Overall, smartphone apps are by far the most practical. After all, you always have your smartphone with you. These apps are user-friendly, offer numerous functions and are usually updated regularly and free of charge. Our clear recommendation is the Carly app. In addition to comprehensive diagnostics, it offers many useful functions, which we will introduce to you in the course of this article.

BMW E91 diagnostic tool
BMW E91 diagnostic tool

Error codes

There are countless control units installed in every vehicle, each responsible for a specific system. Fixed parameters are stored in these control units within which the connected systems are to operate. In case of deviations, error codes are generated and stored. There are tens of thousands of such error codes, also called DTC (Data Trouble Codes), which are divided into two types: internationally standardized codes and manufacturer-specific codes. Almost all diagnostic devices can read general fault codes, but only manufacturer-specific scanners and smartphone apps also understand manufacturer-specific fault codes.

However, all codes follow the same structure: they consist of five characters. The first character refers to the area where the error occurred (B for body, C for chassis, P for powertrain and U for the network/OBD interface). The second character indicates whether it is a standard error (“1”) or manufacturer-specific error code (“2”). The third character (digits 1 to 8) describes the affected system in more detail. Finally, the fourth and fifth characters (digits 00 to 99) indicate the actual error.

Simple diagnostic devices display the rough error code (e.g. P1588 or U0463). Then you need to research online what these codes mean and what actions are needed. Better devices also give a description. Top apps, like Carly, even evaluate the errors and inform you about the priority of troubleshooting.

Control units

Each ECU is a mini-computer responsible for a specific vehicle system, such as air conditioning or engine. Therefore, there are dozens or even hundreds of such control units in the vehicle. They are all interconnected via a data highway as well as with the OBD2 interface, which is the communication backbone of the vehicle.

In most cases, deviations from the stored specifications are directly regulated by the control units and the systems can continue to operate. An error code is generated, but it has little relevance. In case of larger deviations that cannot be regulated internally, a driver warning or a significant error may occur. The Carly app evaluates the error codes and shows you the most important ones in descending order. You will also receive a vehicle condition report – more on that later.

OBD2 interface

The OBD2 interface is an important element of vehicle diagnostics and is located on your BMW E91 to the left of the brake pedal under the dashboard. With a suitable diagnostic device, you can access the vehicle systems via this interface. A high quality OBD2 scanner is crucial to ensure correct communication and avoid possible damage to the ECUs. Connection is either via a cable (for external diagnostic devices or laptop software) or wirelessly (for mobile apps) using an OBD2 device such as the Carly 20-pin scanner and Bluetooth or Wi-Fi.

A brief digression: OBD stands for on-board diagnostics, a standard originally developed in the USA for monitoring emission levels. The future OBD3 standard is expected to allow direct reporting of exhaust faults to authorities, which may lead to mandatory repairs.

The CAN bus for technology enthusiasts

The CAN bus is the communication network in a vehicle. Data packets are exchanged between control units and the OBD2 interface via this system. For example, commands from an app can be transmitted and implemented via the OBD2 adapter to the respective control unit – in a fraction of a second.

Vehicle diagnostics: What happens?

Vehicle diagnostics is about reading and analyzing fault codes. Simple and inexpensive devices can display codes only in their code form, while more advanced devices also provide error descriptions. The best diagnostic devices even tell you how urgent it is to fix a particular fault.

For example, a simple diagnostic device displays only the code B0115. A better device displays “B0115: Short circuit of side airbag leads”. The best diagnostic devices additionally provide an estimate of whether the fault can be fixed immediately, fixed later, or ignored.

Vehicle diagnostics costs and savings

When it comes to vehicle diagnostics, you need to consider two cost factors: the direct cost of diagnostics and the potential savings from catching faults early, before they lead to bigger problems.

Depending on the vehicle model, manufacturer and workshop, the prices for a simple vehicle diagnosis vary between 25 and 60 euros. If you perform a diagnosis every three months, you will pay about 160 euros per year at an average price of 40 euros per diagnosis. You also need to consider the time and cost of making appointments, vehicle transportation, and any additional travel while waiting.

For your BMW E91, the Carly app is an excellent option. It costs about 6 euros per month, plus the one-time purchase of the Carly Universal OBD scanner for 59.90 euros. A high-quality adapter such as the Carly scanner is essential for all external diagnostics. The app gives you access to all the features and helps you save several hundred dollars right away. You can find more information later in this article.

By running regular diagnostics, even monthly, you may be able to detect and correct minor faults early on in certain circumstances before they cause serious damage. This can save several hundred to a thousand euros over the course of the year. By using an effective BMW E91 diagnostic tool, like Carly Scanner, you can increase the life of your car and avoid significant costs.

BMW E91 diagnostic tool
BMW E91 diagnostic tool

The optimal BMW E91 diagnostic tool for you

Based on the information mentioned here, we would like to convince you that the Carly app is the best choice for you. It offers a wide range of additional features, which we’ll get to in a moment. It is also available for download from the Apple App Store and the Google Play Store. The Carly app has already been downloaded over one million times. You can start with the free version of the app, which provides you with a limited, yet impressive set of features. Here are the main features of the Carly app:

  • comprehensive vehicle diagnostics: the Carly app allows you to diagnose your BMW E91 in detail, including fault codes, warning messages and system information.
  • Personalization: Custom ize your vehicle according to your preferences by changing various settings, such as lighting, infotainment system or locking options.
  • Maintenance Support: Receive maintenance alerts and reminders to keep your vehicle in optimal condition.
  • Used car check: Use the app to check used cars for potential problems or tampering before you buy them.

Vehicle diagnostics and vehicle condition

The Carly app not only offers the possibility to read and understand standard fault codes, but also manufacturer-specific fault codes that are specifically relevant for BMW and your BMW E91. The Carly BMW E91 diagnostic tool won’t leave you guessing and provides detailed explanations of the detected errors. But that’s not all: Carly also shows you the health status of your vehicle, ranking the faults according to their severity. A traffic light system is used: green means that your car is in good condition and you don’t have to do anything. Orange indicates that you should perform further diagnostics as there are errors that need to be fixed. Red means that your car has serious problems and immediate action is required.

Customization and coding

Coding may sound technical, but it doesn’t have to be. It’s about setting your personal preferences for many of your BMW E91’s features. You can adjust different settings for numerous areas , such as cornering lights, turn signals, brake lights, corona rings, convenience features, park sensing (PDC), entry assist, power windows, power liftgate, welcome home lights, automatic climate control, engine start-stop, and more. There are hundreds of options and possibilities that you can customize. If you were to do this in a workshop, the cost of each adjustment would be between 30 and 50 euros. However, with Carly you can make as many settings as you want and try different options as well as switch between them.

Carly used car check – a real helper

This feature is exclusive to Carly! When buying a used car, such as a BMW E91, it is often difficult to find a good vehicle. Even the most visually beautiful car can have a manipulated mileage. Speedometer tampering is a serious problem and studies show that up to one-third of used cars are affected. The Carly Used Car Check is a unique feature that queries all relevant ECUs to detect signs of mileage tampering and displays a report accordingly. This way you can judge whether the seller is trustworthy or not, and save thousands of dollars with Carly’s BMW E91 diagnostic tool!

Service reset and more

As an avid car owner, there are some tasks you can do yourself, such as an oil change (see below for some tips). After the oil change, you will need to update the ECU and reset the service interval so that the system recognizes that the oil has been changed and will not display any further service warnings. With Carly, this is not a problem. Carly also helps you register a new battery or perform other maintenance tasks yourself to save even more money.

A short digression: Changing the oil yourself

Oil change intervals are between 15,000 and 60,000 kilometers. You can change the oil yourself, but you should keep a few things in mind. First, make sure you’re using a high-quality oil that meets the manufacturer’s specifications. It would be helpful if you had a way to lift your vehicle and had a catch basin ready for the used oil – spilling it on the ground is an environmental hazard. It is best to change the oil in a well-equipped DIY workshop. By the way: When you buy the new oil, your used oil must be taken back by the seller free of charge; alternatively, you can dispose of it at a suitable recycling facility. Never put it down the drain or in the household garbage.

Retrieve real-time vehicle data

Do you want to monitor parameters like fuel consumption, exact speed, oil temperature or other values in real time while driving? Carly offers a real-time function that allows you to do just that. You just select the parameter you want and you can track it.

Additional functions

Apart from the functions mentioned above, there are many more, such as the emissions test, resetting the automatic transmission, the digital garage (here you can save all the values and forward them as a PDF or by e-mail), checking the diesel particulate filter and much more.

Just download the free Carly Lite version in advance and find out which features are available for your car model.

Farewell workshop?

So does it mean we can say goodbye to the workshop? Unfortunately no. While you can use Carly to reduce your workshop visits and the associated costs, they cannot be avoided entirely. No app can do that. There will always be minor and major repairs that need to be done by a workshop, as well as complex problems that only a professional can identify. However, you can perform minor diagnostics, coding and service resets yourself, saving time and money.



Keep in mind, that every car has different software and modules built-in. Therefore specific features will vary with every model.

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