Majority of our users have ELM327 or compatible devices. The ELM327, with all its known advantages, is an amateur level adapter designed for OBDII family of protocols. It was designed so good so can be used more widely, but this doesn't change the fact it is an amateur level device, that has lack of some features that are very desirable or even mandatory to work in full with modern Electronic Control Modules (ECUs). This statement above is generally applicable to the "derived" adapters, such as OBDLink MX or ELS27.
But some part of our users are professionals in diagnostic and prefer to use professional tools, that are J2534 Pass-Thru adapters. Although this category of users is not numerous, we value them highly as they help us to better understand diagnostic tasks and objectives. So we have added the PassThru support mainly for this category of users. We believe that support of J2534 devices may be also interesting for other categories of users, such as Ford and Mazda enthusiasts, clubs etc.
It should be counted that for now the support of J2534 adapters is rather experimental and gives no drastical advantage to user, except much better performance (up to 2 times faster than any white-label adapters like OBDLink MX and ELS27, and 5-20 times faster than fastest of china clones). But the potential of J2534 devices will be explored in future versions of FORScan.
Let's list all the advantages of J2534 Pass-Thru devices:
1. Performance. In contrast to ELM327, with its text-based interface designed for serial port communication and limitations of AT-commands based protocol, J2534 Pass-Thru devices are initially designed for high performance and flexibility.
2. Protocol features and flexibility. "Native" vehicle protocols require more than OBDII family of protocols. For example, "long" CAN requests (sending a lot of data per single request) - ELM327 is not able to do it. Another example are so-called "presence" requests that should be sent to ECU in precisely fixed time intervals. Another example is MS-CAN support. This is not a full list. FORScan and other software (ELMConfig, Focccus etc), have to "emulate" such kind of things, and sometimes these emulations are reallly a work of art, often more complex that the ECU programming itself.
But there are features that cannot be emulated in ELM327 at all. For example, support of programming voltages, required to reflash some ECUs.
3. Reliability. J2534 Pass-Thru are intially designed for dangerous operations (ECU reflashing) and professional usage. So in general case their reliability is higher (although it depends).
What are drawbacks? Most significant is their cost. Cheapest of Pass-Thru adapters and china clones cost at least $200-300, known brand solutions cost $500-1500 and higher. Another problem is that not all of Pass-Thru devices support MS-CAN. Because MS-CAN support requires part 2 of J2534 standard (SAE J2534-2), and J2534-2 devices are usually more expensive (CanTieCar and china clones are an exception)
Let's briefly review J2534 usage in FORScan.
If Connection type is set to Auto, FORScan looks for J2534 devices first of all. If none is detected, FORScan looks for WiFi, FTDI, COM etc. So Pass-Thru devices are the priority.
If more than one J2534 device found in the system, FORScan shows a dropdown box with list of J2534 devices:
This computer has Openport 2.0 and CanTieCar v3 devices installed.
User can set the connection type to J2534, and select a specific J2534 device to select a preferred device.
Let's look at J2534 adapters we used for testing, Openport 2.0 and CanTieCar v3.
A. Openport 2.0
Advantages: Cheapest of branded J2534 adapters ($170 at the moment we purchased it). Can communicate with HS-CAN and Ford ISO modules, works good with them.
Drawbacks. Doesn't support SAE J1850 !!!, although this protocol is claimed everywhere on their site (see screenshot above as an example). Also doesn't support J2534-2. So in case of Ford, Mazda, Lincoln and Mercury vehicles is applicable for CAN vehicles only (Ford/Mazda after 2002, and may be for Mazda 1996-2002 too, we had no chance to check). Also, it seems the Openport project is not developed anymore or developed extremely slowly.
Resume: not fully applicable for Ford, Mazda, Lincoln and Mercury, but can be partially used for new vehicles (partially - because no MS-CAN support) if there is no other adapter.
B. CanTieCar v3
Advantages: Quite advanced adapter, developed intensively, with multiple non-standard features, in addition to J2534 and J2534-2 features. Can emulate other devices. Relatively cheap (just slightly more expensive than Openport 2.0), but in terms of functionality can compete with (and win) many of professional (and much more expensive) devices. Very good and responsible support (much better than, for example, Openport, ELS27 and Scantool one).
Drawbacks: the product is actively developed but not tested (so in fact tested by users). So bugs are very possible (we helped to fix several ones just implementing support of this adapter).
Resume: probably the best choice in terms of price/quality.
The above devices are 2 ones we tested on. But the J2534 functionality is designed in the way it should work with any Pass-Thru device. And this design works - in one of our external tests (happended already after the version 2.2.1 was released) we were really very surprised to find out that FORScan perfectly works with china clone of Ford VCMII (purchased for $300 or so on aliexpress), including MS-CAN/J2534-2 functions.
We will update this article together with corresponding FORScan functionality.