Supported Hardware Interfaces

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This manual applies to Version 1.06 of freediag

Table of contents:

Electrical Interface Types

There are various common hardware interfaces used for diagnostic interfaces to vehicle electronic control units (ecus). Most manufacturers use one or two such interfaces for all systems on a vehicle. These include:

ISO9141 and ISO14230 are essentially compatible at an electrical level (with the exception that the latter will work on 24 volt vehicles).

The freediag protocol stack supports the above list with the exception of the CAN. The US OBDII standard and the European EOBD standard for communicating with emissions related ECUs do not mandate CAN support.

The ISO protocols are generally used by European Vehicles, and the two SAEJ1850 types by Ford and GM.

At a software level, ISO14230 is a vastly extended ISO9141-2 protocol that supports much longer data frames and much quicker communications startup with the ECU.

Further information can be obtained from:

About Smart/Dumb classification

There are two general types of interfaces, referred to as "active" / "smart" (with an onboard microcontroller) and "passive" / "dumb" (no mcu, only signal level translation and possibly opto-isolation).

Freediag Supported Interfaces

Freediag contains various drivers for different adapters that connect the PC serial port to a vehicle. Certain interfaces support more protocol types than have been implemented/tested within a driver, and some interfaces need to be ordered with special attributes (such as their address) to work without recompiling the freediag software library.

  1. Generic dumb serial adaptors

    Freediag Driver: DUMB (diag_l0_dumb.c)
    *** read doc/dumb_interfaces.txt !!! ***

    These are generic serial to K-line interfaces, typically very simple circuits *without* an onboard microcontroller.
    VAG409 / KKL409 interfaces fall in this category. Other examples include:
    Andy Whittaker's OBD-II ISO9141 interface;
    (website down)

    Silicon Engines ISO 9141 interface:
    (website down)
    It is supplied in a robust box with lots of lights. This interface was used to develop the first bits of the freediag project. It is functionally the same as the above two interfaces (with the exception of all the lights and the box).

    Jeff's OBD-II ISO 9141 interface:
    This site shows you how to build a generic serial to ISO9141 interface.

    List of configurable items in "set" submenu :
    dumbopts [opts] Sets dumb-interface-specific options. Use set dumbopts ? to get details.
    See doc/dumb_interfaces.txt for further information
    port [devname] Sets serial port to use. "port ?" will show auto-detected ports not currently in use.

    Availability : various vendors, or DIY projects

  2. B.Roadman ISO9141/VPW/PWM interface:
    (website down)
    Freediag Driver: BR1 (diag_l0_br.c)

    Another commercially available interface, we haven't yet tested the ISO9141 side of the interface (supports address 0x33 only), and it does not support ISO14230. Future versions will support ISO14230 and we used this interface to develop the J1850-VPW/PWM support in Freediag. Thanks to B. Roadman for the donation of hardware to the project.
    These qualify as "smart" interfaces.
    Availability: questionable

    List of configurable items in "set" submenu :
    port [devname] Sets serial port to use. "port ?" will show auto-detected ports not currently in use.

  3. Multiplex Engineering VPW, PWM, and ISO 9141-2 interface:
    Freediag Driver: MET16 (diag_l0_me.c)

    When ordering this interface you must order a T16 type interface. Multiplex Engineering produce two varieties of the T16 interface:

    Many PC's do not provide enough power to drive the T16-002 interface and thus errors will occur (and "checksum error" messages will be printed by the freediag software). As the T16-003 has no opto-isolation there is a slight risk of damage to the PC. According to the manufacturer the risk is low and is negligible unless the vehicle is connected to a battery charger.

    When ordering an interface an interface that operates at 19200 baud and uses address 0x38 should be specified, or simple modifications to diag_l0_me.c and recompilation will be needed.

    The T16-002 interface was used to develop support for smart interfaces in freediag, it worked on a modern Sony Laptop but not on various branded PCs tested.
    Availability: See website

    List of configurable items in "set" submenu :
    port [devname] Sets serial port to use. "port ?" will show auto-detected ports not currently in use.

  4. ELM32* based interfaces:
    Freediag Driver: ELM (diag_l0_elm.c)

    The ELM32x ICs are smart protocol translators that are frequently found in recent USB->OBD cables. Freediag partially supports these devices. Be aware that many so-called ELM32x adapters use a cloned but not completely compatible IC. Most cheap devices sold on eBay / Amazon will be clones.
    These qualify as "smart" interfaces.
    Availabilty: IC by itself direct from vendor, or assembled interfaces from various third parties

    List of configurable items in "set" submenu :
    port [devname] Sets serial port to use. "port ?" will show auto-detected ports not currently in use.

  5. CARSIM interface:
    Freediag driver: CARSIM (diag_l0_sim.c)

    The CARSIM interface allows testing of higher levels (L2, L3) without having an actual car connected. It reads requests and responses from a file.

    This was coded by vnevoa ~2004. From his presentation:
    Basically, it is a file reader and parser that searches for the byte sequence that is being sent to the car, and if it finds any number of answers for it, it simulates the responses from the car. I included a simple parsing mechanism to simulate whatever test values we want by placing a few text tokens inside the response sequences, which get translated into byte values through specific functions.

    List of configurable items in "set" submenu :
    simfile [filename] Select simulation file to use as data input. See freediag_carsim_all.db for an example

Compatibility Matrix