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Engine Diagnostic Pulse Counter — Parallax Forums

Engine Diagnostic Pulse Counter

Jay KickliterJay Kickliter Posts: 446
edited 2010-03-25 22:31 in Propeller 1
Is anyone familiar with pre-ODB engine diagnostics? I'm trying to trouble shoot the climate control system in my 1995 MB E300 Diesel. They use an error reporting system that outputs pulses, after grounding a particular pin on the diagnostic unit. I know, pretty vague description, but I can't find much information on it. Apparently it is just a front end; the computers communicate on CAN Bus. I've been away from the Propeller chip for a while (got tired of being inside all the time). I'd like to make a small board that plugs into all the diagnostic pins and stores the errors and displays the meanings, not just a code.

So two requests: a more detailed explanation on the early computers and diagnostics than can be found in the wrenchers forums, and the way to set up a counter to count the number of pulses, regardless of duration, without bouncing. I think it pulses pretty slow; slow enough to count them visually with an LED.

Comments

  • pmrobertpmrobert Posts: 677
    edited 2010-03-23 19:28
    I only have hands-on with the Japanese versions of the blinky-count concept. Those would blink patterns that are time dependent - say 2 1000ms blinks, 1000ms pause, 4 500ms pulses a 4000ms pause, then repeat. This would be a code 24, for example. Multiple report codes could exist and were separated by the by the 4000ms pause. The whole thing repeats until powerdown and the activating jumper pulled. I'm fairly certain you're going to need to know the specific timing patterns and codes returned by that/those ECUs. MB possibly uses a Bosch unit; the only Bosch unit I've seen was in a Porsche and was similar to the Japanese format in it's reporting method. This may not be more than you've already found, just thought I'd throw it out there...
  • mojorizingmojorizing Posts: 249
    edited 2010-03-24 01:55
    The ECU of the porsche only reported codes thru it's CEL, not codes from the climate control.

    This describes the process.· http://www.durametric.com/porsche964faultcodes.aspx

    Also, this site·has links to the protocal that porsche, and maybe MB used pre-OBDII

    http://pcbunn.cithep.caltech.edu/jjb/Porsche/Motronic-964-Porsche.htm

    Especially check out the Yahoo! Group "opendiag"·









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  • kwinnkwinn Posts: 8,697
    edited 2010-03-24 02:47
    At the rate the pulses are coming in why bother with the counters. You could use waitpeq/waitpne with waitcnt in a simple spin program to measure the time between pulse edges and use that to decode the bit patterns.
  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2010-03-24 06:00
    I remember doing a pulse code display for a Mitsubishi and I did the whole pulse counter and LCD interface in an 8-pin PIC. Perhaps just maybe the Prop can do the same smile.gif

    A simple Spin program will be more than sufficient for this, you just need the information on the pulses themselves. Hardware-wise I would just use a high value resistor feeding into a Prop Pin with a pull-down before it.

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  • JomsJoms Posts: 279
    edited 2010-03-24 06:32
    Too bad it isn't the CEL coming on. I have found a universal reset tool that works with most all models. The small roll of black tape sold at most hardware stores (commonly called electrical tape), works wonders for perminatly hiding the light.

    OK, sorry for the humor here, but I just couldn't resist. Reading thru the posts and a few people were mentioning the CEL and this came to mind. Sorry...
  • Jay KickliterJay Kickliter Posts: 446
    edited 2010-03-25 14:31
    I built an LED blinky box and hooked it up to the system. I realized it's active low, and a test is initiated by pulling pin you want to test to ground for 2-4 seconds. Unfortunately, I didn't realize that the test affects the system, so it's not something that can be left on. I'll just make another box with the codes stored inside and a spare two-line LCD I have laying around. Hopefully the system allows you to test more than one pin at a time, since it's so slow. Probably doesn't.
  • TappermanTapperman Posts: 319
    edited 2010-03-25 20:48
    @Jay Kickiter

    Have to you tried this site?

    ········ http://www.obdii.com/connector.html

    It shows full compatibility for S 320, C 280, SL 320 Models, but your car predates the standard by one year.

    Post Edited (Tapperman) : 3/25/2010 8:55:34 PM GMT
  • icepuckicepuck Posts: 466
    edited 2010-03-25 22:31
    Your best bet would be an OEM service manual with electrical/wiring diagnostics. Having pin outs will make things alot easier. Go to the parts dept. of your local dealer and see if they will allow you to order one.
    -dan

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