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Info guides and mods

OBD Upgrade

OBDII may be a standard but manufacturers were given a long leash which came to protocols and the manufacturer specific pins. I will tell you more and tell you my idea.

Modification Details




About The OBD (On Board Diagnostic) Port

In 1996 it became a requirement that all vehicles sold in the USA had to have an OBD port.
Because of this, almost all manufacturers started to include them in all of their cars.

One requirement of the OBD port was that it had to be within 3 feet of the driver and had to accessible without the use of any tools. Home car diagnosis was born.


OBD Protocols

Although the connection was the same, the manufacturers were allowed to use what ever protocols they saw fit. A protocol is the method by which data is sent from one place to another. Although there are many protocols used, there are 5 main ones.
  • J1850 VPW
  • J1850 PWM
  • ISO 9141-2
  • ISO 14230-4 (KWP2000)
  • ISO 15765-4 (CAN)

    The current smart uses ISO 14230-4 to send ECU data to the OBD, most European and Asian manufactured cars use ISO 9141-2.


    The Future Of OBD

    From January 2008 a new law was passed. All cars to be sold in the USA have to use the ISO 15765-4 (CAN) protocol. Looking at how the market reacted last time I can see that almost every car created from then on will use the CAN (controlled Area Network) protocol.

    Even in the run up to this law, manufacturers are swapping to CAN. Even the mighty Honda, who have been using ISO 9141-2 since day one have moved over to CAN on the new European Civic. The rest of the Honda range will follow along with many others.

    Is This Good Or Bad?

    It's a very good thing if you are into home diagnostics as you won't have to buy a reader that just does a few cars or spend a lot of cash on a multi-protocol reader.
    It's also a very good thing if you have shares in Bosch as they invented the CAN protocol.

    Speed Comparison

    This is where CAN beats the others, it can access data far quicker than the other protocols.
  • SAE J1850 VPW (10.4 kbaud)
  • ISO 9141-2 (10.4 kbaud)
  • ISO 14230-4 KWP (up to 10.4 kbaud)
  • SAE J1850 PWM (41.6 kbaud)
  • ISO 15765-4 CAN (up to 500 kbaud)

    This means you can track fast moving values with a lot more accuracy plus if you are running a laptop or a PDA with a virtual dashboard, the dials will update far quicker.


    What Has This Got To Do With Smarts?

    Although the current smart uses ISO 14230-4 to transmit data to the OBD,
    the SAM unit, ECU, ESP, Speedo and other electronics all use a CAN bus to communicate with each other.

This is because the ECU is a Bosch unit and they invented it.

So What's The Plan?

The idea is purely conjecture at the moment but there seems to be no reason why the CAN bus cannot be extended to the existing OBD port and used for diagnostics.

The CAN bus uses a CAN high and a CAN low wire to transmit data. Both of these are available to and from every main electronic unit in the smart. The nearest CAN high and low to the OBD are found on the back of the speedo.

The speedo actually has 2 sets of CAN wires, one set is from the SAM and one set from the ESP module, I assume the speedo is just an interconnect between the two.

Pin 14 (pink/white) CAN high
Pin 15 (brown/red) CAN high
Pin 16 (white/black) CAN low
Pin 17 (pink/green) CAN low

At the moment I cannot confirm if one, both or neither will do the trick.

The ISO 15765-4 (CAN) standards say that OBD pin 6 should be CAN high and OBD pin 14 should be CAN low. By my reckoning there is no reason why the CAN pins can't be added and the CAN system accessed via a laptop and some propriatory software.


Important

Before you all get carried away, this CAN bus will not be carrying
diagnostic info but it will be carrying certain info such as:

  • Revs
  • Speed
  • Fuel level
  • Coolant temp
  • Gear number

    It's not going to be as simple as plug you laptop into it, write a quick program and access the info but the information certainly is there if you have the knowledge to get it.

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