The short answer
A diagnostic tool plugs into the car's OBD2 port and talks to its control units. Depending on the model, it can do five things: read and clear faults, show live sensor data, reach every system (ABS, airbag, gearbox, comfort…), carry out servicing jobs such as the oil reset or releasing the electronic parking brake and, on the higher-end ranges, activate components and code control units.
A cheap OBD2 code reader only does the first, and only on the engine. For everything else you need a proper diagnostic tool.
Plenty of people buy their first scanner to switch off the engine warning light, and two months later find they can't change the rear pads because the car has an electronic parking brake. It happens the other way round too: small garages pay for a top-end tablet and then use 10% of what it can do.
That is why it pays to be clear about which functions exist and which ones you will really use. We go through them from the most basic to the most advanced, with real examples from the iCarsoft range.
- OBD2 code readerReads and clears engine and emissions faults. Nothing more.Example: the OBD2 mode on any iCarsoft tool
- All systems + serviceReaches every control unit and handles routine servicing.Example: CR Pro and V2.0 single-brand tools
- BidirectionalAlso sends commands to the car to test components.Example: CR Pro+, CR Max P
- Coding and programmingChanges control unit settings or loads software onto them.Example: CR Max P (coding), CR Ultra P (programming)
Reading and clearing faults
It is the first thing any tool does, and the one you will use most. When you connect it, it queries the control unit and returns the stored codes, for example P0420 (catalytic converter) or P0300 (misfire), with a plain-English description.
Every petrol car sold in Europe since 2001 and every diesel since 2004 has OBD2 (known in Europe as EOBD). That part is common to all makes and is designed to monitor emissions. It includes:
- Confirmed fault codes and pending codes (faults the control unit has seen once but not yet confirmed).
- Clearing codes and switching off the warning light.
- I/M Readiness, which tells you whether the emissions monitors are ready. Very handy before a roadworthiness test such as the NCT or MOT.
- Tests for lambda sensors, the EVAP system and on-board monitors.
- Vehicle data: VIN and calibration numbers.
One piece of advice we give a lot: don't clear anything until you have noted the code and the freeze frame. If the fault is real, the light comes back on and you will have lost the information that would have helped you find it. We go through it properly in how to clear the engine warning light.
Live data and freeze frame
A code tells you where to look, but not always which part has failed. That is what live data is for: the tool shows you, in real time, what the sensors are reading. Engine temperature, revs, boost pressure, battery voltage, fuel trims, the speed of each wheel…
The freeze frame is a snapshot of that same data at the exact moment the fault was logged. If the fault only appears from cold or at a certain speed, that is where you will see it.
On tablets such as the CR Max P you can graph several parameters at once and record them to review later, which is how intermittent faults really get found.
Diagnostics on every system
This is the big difference between an OBD2 code reader and a diagnostic tool. Generic OBD2 only sees the engine. If the warning light on your dash is for the ABS, the airbag or the gearbox, a basic reader will tell you there are no faults.
With each manufacturer's specific software, the tool gets into every control unit: engine, gearbox, ABS/ESP, airbag, steering, climate control, body, comfort, instruments… On each one you can read and clear faults, view live data and check the part number and software version.
Every current iCarsoft tool does this. The difference is how many makes they cover: the CR Pro works with 58 makes, while a single-brand tool such as the VAWS V2.0 focuses on one group (in this case Volkswagen, Audi, SEAT and Skoda). If you are torn between the two, multi-brand or single-brand? will help.
Service functions
These are the procedures the car demands after servicing or after certain parts are replaced. Without them the reminder won't go off, the new part won't work properly or you simply can't finish the job. These are the nine most common:
| Function | When you need it |
|---|---|
| Oil reset | After changing the oil and filter, to reset the service reminder. See how it's done |
| EPB (electronic parking brake) | To open the rear callipers and change pads or discs. See how it's done |
| DPF | To regenerate the particulate filter or register a new one. See how it's done |
| BMS | To register a new battery so the alternator charges it correctly. |
| SAS | To calibrate the steering angle sensor after wheel alignment or steering work. |
| Throttle (ETC) | To relearn the throttle body after cleaning or replacing it. |
| Injector coding | To register the codes of new injectors with the control unit. |
| ABS bleeding | To bleed the brake circuit by running the ABS pump. |
| TPMS | To register tyre pressure sensors and switch off the warning light. See how it's done |
Those nine come on the CR Pro and the V2.0 single-brand tools. Beyond that the list grows a lot: the CR Pro+ has 48 functions, the CR Max and CR Max P reach 50, and the CR Ultra range has 40, with things like EGR, AdBlue, NOx sensor, Start&Stop, air suspension and automatic gearbox learning.
Watch out with the V1.0 tools. The older V1.0 single-brand range only does oil reset and steering angle. If you want electronic parking brake or DPF, you need a V2.0. We compare them in V1.0 vs V2.0.
Active tests or bidirectional control
A bidirectional tool doesn't just listen to the car: it gives it orders too. You can switch on the fuel pump, run the radiator fan, operate a window, open the EGR valve or run the ABS pump, and see on screen whether the component responds.
It sounds like a detail, but it saves a lot of money. If the fan doesn't start when you command it from the tool, you know the problem is the fan or its wiring and not the temperature sensor. Without that test, you usually end up replacing parts that were fine.
The CR Pro and the V2.0 single-brand tools are not bidirectional. The CR Pro+, CR Max, CR Max P and the CR Ultra range are. If you are choosing between the CR Pro and the CR Pro+, this is the difference that matters most; it is explained in CR Pro vs CR Pro+.
Control unit coding and programming
They are two different things and it is worth keeping them apart:
- Coding means changing the configuration of a control unit that already works. For example, adapting a replacement part, enabling a feature the car has from the factory but switched off, or telling the car you have fitted a tow bar. The CR Max and CR Max P code across 8 brand groups: BMW, VAG, Hyundai/Kia, Ford, Mazda, Renault, Chrysler/Jeep/Dodge and Subaru.
- Programming means loading software onto the control unit, either to update it or to get a new one working. The CR Ultra P does cloud programming for 13 makes and comes with the J2534 pass-thru compatible CR Link VCI, which lets you use the manufacturer's official software from a PC.
Before coding or programming: connect a battery support unit, don't unplug anything while the process runs and write down the original coding. If it is interrupted halfway, you can leave a system not working.
Other functions that make a difference day to day
They don't make the headlines, but you notice them when you use the tool often:
- VIN identification. The tool reads the chassis number and recognises the make, model and year without you hunting through menus. It avoids mistakes when picking the engine or version.
- Reports and history. It saves the cars you have diagnosed and lets you share the report, which is very handy if you work on other people's cars.
- Updates. The tablets update over Wi-Fi; the button-operated tools with the TF card and a PC. On the CR Pro, CR Pro+ and CR Max range they are free for life, with no subscription. On the CR Ultra they are free for 3 years, after which renewal is optional.
- CAN-FD and DoIP. These are the protocols many recent cars use. If your car needs them and the tool doesn't support them, it won't connect. We explain them in what DoIP and CAN-FD are.
Which tool you need for the job
If you look after your own cars and the family's, you will rarely need more than a tool with every system and the service functions. Active tests start to pay off when you are genuinely repairing faults, and coding and programming are workshop territory.
| What you want to do | This is enough |
|---|---|
| Read faults and do servicing on cars of several makes | CR Pro |
| The same, but for one make or group only | A V2.0 single-brand tool |
| Track down faults with active tests | CR Pro+ or CR Max P |
| Code control units | CR Max P |
| Program control units and work with J2534 | CR Ultra P |
| Motorbikes | MT PRO |
| Trucks and heavy vehicles | HD V4.0 |
| Tyre pressure sensors | TPMS V800 |
If you are setting up or equipping a garage, there is a more detailed guide in which diagnostic tool to buy for a garage.
Three questions before you buy
- Which cars will you be plugging into? If they are all one make or group, a single-brand tool is cheaper. If they are a mix, go multi-brand.
- Will you be repairing or just servicing? For servicing, every system plus the service functions is more than enough. For repairs, look for bidirectional control.
- How old are the cars? On recent models, check that the tool supports CAN-FD and, if needed, DoIP.
With those three answers the choice narrows down to one or two models. And if you are still unsure, send us the make, model and year and we will tell you which one suits your car.
