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Connecting To An Automotive Diagnostic Computer? 26

Posted by Cliff from the interfacing-with-your-engine dept.
An Anonymous Coward writes: "I was wondering if anyone has tried to hook up a PC to the diagnostic computer on an automobile. Each time the little idiot light on my Blazer comes on I have to cough up $20 - $40 just to find out what the problem is. This seems to me like an amusing and only moderately difficult hack - I can't believe that I am the first person to think of it. However, I can't seem to find any information on the topic at all."
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Connecting to an Automotive Diagnostic Computer? More

Connecting to an Automotive Diagnostic Computer?

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  • Re:Diagnostics with a simple multi-meter (Score:1)

    by Anonymous Coward
    Up, Up, Down, Down, Left, Right, Left, Right, Gas, Brake, Start gave me infinite Gas.

  • Here is a link to anECM scanner [aeswave.com] (a device that will read the diagnostic codes on modern cars) for only about $500. It looks like it can handle a wide variety of Chrysler, Ford and GM vehicles built between 1984 and 1995.

    The company [aeswave.com] sells a few other interesting toys that could be of use to automotive/electronics geeks.

    Otherwise, there are some links I found along the way: I got these links simply by doing a Google search on "engine computer diagnostic". There were many more (about 4000 pages worth) but I got tired of skimming through them (I was averaging about 2 usefull hits per page).
  • And at a really funky baud rate, like 4312. You have to buy the right chipset and set it up just right. If your time has value, look for the manufacturer's diagnostic consoles on ebay or something. It'll be cheaper.

    See also www.obd-2.com [obd-2.com] (if your time has no value and/or you just want to tinker).

  • Indeed, if you go to an auto parts store you'll find various auto diagnostic devices, labeled for various makes of cars. Personally, I'd rather get an interface for a PC so I can have a computer in the car monitoring for faults (among other things it will be doing); if something breaks it would be nice to get an audio/text warning and explanation.

    For that matter, I had difficulty a couple of years ago when an alternator failed and the idiot light wasn't visible through my sunglasses...

  • Diagnostics with a simple multi-meter (Score:3)

    by dead_penguin ( 31325 ) on Friday July 21, 2000 @09:36PM (#913828)
    Quite some time ago I was searching around the net for exactly the same thing, just out of curiosity. Unfortunately I didn't keep any of my bookmarks on this (and they've probably 404'd anyways), but many manufacturers encode the error "codes" as a series of pulses. Using a multi-meter or a simple 12V bulb, you can count them and get the error code. They're not even encoded in any way (BCD or whatever), but rather the number of pulses is directly equal to the code. Building a simple circuit to record the error codes and later dump them in a serial port (or parallel if that's your thing) shouldn't be too difficult.

    A Google search turned up some examples of codes, so they're out there; you just have to look!
    Ford Probe [scpoc.com]

    Eagle Talon [myzero.com]

    Most of the better shop manuals you can buy also have most of these codes. Take a look through some of the aftermarket books like those from Haynes or Chiltons or whatever you can find.
  • Having to reset my master computer a few cars back, I found most cars built after '85 have a way to get a dash light to pulse the codes. With that particular car, you keyed the ignition on-off 3 times to put it in "diagnostic mode". It pulsed any error codes stored with the check engine light. The big problem of course is cars that have this feature also have more advanced emission control and auto-calibration systems that will spew lots of errors at you because their sensors aren't in the right state at that point. The same problems exist with the cheap generic daignostic tools you can get at better auto stores.
  • Might not even need the meter... seem to remember that on one car we had, you could get the error codes to flash on one of the indicators on the dash by doing something odd while turning the key.

    With most (all?) computer-equipped GM vehicles, if you short the appropriate terminals on the ALDL (Assembly Line Diagnostic Link) connector and switch the ignition on, the "Check Engine" light will start blinking out any stored trouble codes. A decent aftermarket manual will tell you which terminals to short and what the different trouble codes mean for your vehicle. (At least the Haynes manual for the '83 Celebrity I used to drive has this info.)

    Car-parts stores also sell a gadget that hooks into the ALDL and blinks out the trouble codes, but why spend the $20-$30 they're asking when a two-cent chunk of wire will do the same job?

    _/_
    / v \
    (IIGS( Scott Alfter (remove Voyager's hull # to send mail)
    \_^_/

  • Might not even need the meter...
    seem to remember that on one car we had, you could get the error codes to flash on one of the indicators on the dash by doing something odd while turning the key.

    as the previous poster said, Chiltons or similar would probably be a good place to look.
  • If you have a Holden VN,VP,VR or VS this [techedge.com.au] might be of interest to you.
  • that's funny cause my car accelerates when I push down on the accelerator too! :-)
  • The interface might be designed to be difficult, as a way to prevent competitors (other auto companies and third-party diagnostic providers) from reverse-engineering the protocols, and offering competing products. Yeah monopoly/oligarchy.

    Anyway, it may not be a trivial hack. I suggest that you think about asking your car mechanic (You are friendly with him, aren't you? If not, ask another shop.) if there are any specs in the repair manuals, or if he can share anything with you. He may get nervous (NDAs for diagnostic operators), or mislead you (he'll make less money if you succeed), so be careful about who you ask and how you ask.

    And if you have any success, please share it. I can imagine a convergence of car guys and computer guys working on their cars, crossing social boundaries, living in harmony with each other and nature, learning from each other, ... uh, whoops. How did I have a flash-back to the 60's when I was born in the 70's?

    Good luck with your car.

    Louis Wu

    "Where do you want to go ...

  • Alright, the first thing you need to do is to go down to your local autozone/shucks and buy a book of your partiular model. Inside, it should tell you how to enable your code and how to decipher it. For example, I have a 95 dodge neon, and the procedure goes like this:

    OBD stands for On Board Diagnostics, and is a federally mandated specification for new cars, largely aimed at reducing emissions. The car logs certain problems that occur, and activates the 'Check Engine' light (CEL) to alert the driver. A mechanic with the proper DRB Scan Tool can the review this log in some detail to assist in repairing the problem. The most direct benefit is that owners can access some of this information themselves. Certain codes will set off the CEL while driving; some do not. It is a good idea to check for hidden codes occaisionally.

    To read any OBD codes, perform the following sequence.

    1) Cycle the ignition key ON-OFF-ON-OFF-ON within 5 seconds.

    2) Count the number of times the 'Check Engine' lamp on the instrument panel flashes on and off. The number of flashes represents the code. There is a slight pause between the flashes representing the first and second digits of the code. Longer pauses separate individual codes. For example, flash-flash-flash [pause] flash-flash represents the code 32.

    You should have a similar sounding thing in your book. Most of the time the problem with the "service" light means that you need to fix somthing electrical (usually a 4-5$ part and fixable yourself, the guy at the auto parts store can usually tell you how to install it for free) or your timing is off for whatever reason.

    My dad has had caddies since the late 70's, and the ODB readings were accessable through his electronic climate control by pressing and holding certian buttons, but good luck finding a book on caddies with that kind of information, caddy ODB numbers are only listed in special dealer "how to fix everythig" books from the GM press that we managed to find at a swap meet in seattle on weekend.

    where i got the info on the neon was at http://www.neons.org/faq/FAQ_ET.html

  • Unfortunately this doesn't work on anything made past about 93 or 94. The automotive industry switched over from the older connector where you could short two pins on the connector and then read the pulses on the dashboard to a new system where you have to have some type of a computer to connect to the car's computers. I've been unable to find any info on this, even though I tried quite a bit -- it seems it's quite proprietary. I do believe you can buy a simple computer that's designed to do this for about 200 bucks at your local auto store -- if somebody were to get one of those and reverse it I know I'd be grateful.
  • First oof, I need more information to be able to help you out. What year is your Blazer? This is the most important piece of information. If it is older than 1995 then you can do it yourself with a paperclip. However, if it is newer than 1995 you're out of luck. The only way to get those codes is to let an automotive technician look at it. If it is older than 1995 take a paperclip and bend it into a U shape. With the ignition turned of, place the paperclip into the upper right two oenings in the diagnostic connector (ALDL), located under the dash. Turn the key on and watch the engine light. Count the number of time that it flashes. It will repeat each code three times. The first one should be a twelve. This means that the computers diagnostic circuitry is ok. It is represented like this: flash pause flash flash long pause flash pause flash flash long pause flash pause flash flash. If there are any other diagnostic codes they will flash after this one, otherwise code twelve will flash repeatedly. Go down to your local library or Autozone. They usually have Chilton's manuals that include the defenition of the codes. In fact Autozone should be able to print up a list of the codes for your specific vehicle form their computer system, free fo charge. Good luck.
  • I may have the location of the two connectors for the paperclip incorrect. GM positions that ALDL differently in some of its vehicles. They are always located next to each other at the upper or lower end of the connector. Again, this is information that Autozone should be able to verify for you.
  • Two errors here. 1) Make sure that anytime you work on a modern vehicle you use only a high impedance multimeter and never use an analog one unless specified by the manufacturer (ie: Ford EEC IV diagnosis). Using the wrong multimeter could cost you a lot more than the $40 it's costing you now. 2) A digital multimeter will not react fast enough for you to read the codes that are produced. On a GM vehicle this is really a simple task. See my response below for more info on how to go about doing it.
  • See Snap On [snapondiag.com] diagnostic tools for professional grade scanners. The MT2500 [snapondiag.com] can connect to a PC, the others may be able to as well.
  • Chrysler. Turn the key to run, then off.. Run, off. Run. Off.. I think it's three.. then the light will start flashing. i think 55 was end of code.. the rest are in the service manual ;)
    I'm wishing there was a similar one for my firebird, had a few problems a couple months ago that knowing the code would have been nice. Nice, as in, can i keep driving this cause i'm too lazy to bring it back to the dealership =)
  • My dad always bought the service manuals when he or my mom bought a new car. They're VERY handy 5-10 years down the line, when you're staring at a random piece of equipment that you just fixed, and now you can't remember where it went
  • Um. Better not tell the oil companies, they'll sue your, saying your use of that cheat violates the DMCA!
  • This guy [tsukuba.ac.jp] has incredible "true" hacking skills. Whether it's cars, arcade boards, even designing a user-friendly gameboy cartridge reader... unfortunately, not all of his site is in English, and I think he only has hacks for cars he owns... He might be able to provide some good starting info though...

  • I use stuff like this all the time. I often have my problems diagnosed before I drive into the dealer. I have a Volkswagen and use the Ross-tech [ross-tech.com] VAG-COM. The now defunct CarComp also had a great tool available for similar purposes. Conveniently, the hardware interface also works for my Dodge truck with different software.


    This guy [mindspring.com] seems to have what the poster is looking for. He covers building your own tools for GM cars.

  • While you can use a multimeter, test light, or such to retrieve the codes from the onboard computer, another way to do this is with a number of 'computer code retrievers' on the market.

    I saw some devices mentioned above that do this job (and probably alot more judging from the pricetags), but if you want just a device that spits out the code, this would be your thing. Usually they come with a book/papers that tell you what each code means (lean oxygen sensor, bad fuel sylenoid, etc). This box, roughly the size of a TI graphing calculator (but not nearly as good a display, if one at all) has a cable interface/wires coming off it that you hook into the computer system. I know on my dad's Oldmobile station wagon (ha!) you plugged into the computer through a wire harness in the glove compartment. On my Ford Tempo I believe you hook up through a wire harness that is under the hood. So it'll vary, but should be easy enough to find, heck the book that comes with the decoder device will probably give you an idea of where it plugs in.

    I tried to find a link to one on the web, but could not unfortunately. However I know Wal-Mart, Napa Auto Parts, Autozone, and several other auto parts dealers carry these devices. I'm sure if you looked around or asked someone in their store they would know what your talking about. I know one in particular that works on both GM and Ford cars. They cost about $25-$40 depending on the brand and probably some of the bells and whistles.

    If you already have a multimeter and can get the probes onto the right pins to get the code, I would say just go that route.

    Bruce

  • I have a friend who works on diesel trucks. He once showed me exactly what the diagnostic computer can do. This computer could change the idle level of the engine, it could even accelerate the engine as if someone was pushing down on the gas pedal. One thing that was a little scary is that computer kept a log of how the truck was driven (idle time, shifting habits, speeds, etc.)
  • So, you want to talk to your car's computer? OBD II is the standard protocol (On Board Diagnostics v2). As of about 1996, most all cars use this protocol, and also have the standard OBD II connector and hardware interface. Typically the connector will be inside the car, under the dash or behind the ashtray, someplace like that. The device your mechanic will plug into it is called a "Scantool". Some manufacturers of these include Actron and Snap-On.

    The standards are documented in SAE (Society of Automotive Engineers, http://www.sae.org/) publications SAE J1978 (OBD II Scan Tool) and J2201 (OBD II Scan Tool Universal Interface) and a slew of supporting documents. I see on their website they are selling a book with a collection of these ("SAE On-Board Diagnostics for Light and Medium Duty Vehicles Standards Manual") They are not trivial to interface to.

    Prior to OBD II, there was a multitude of "standards" and you had to get a different scantool, or a different interface module, to deal with each of them. Each vehicle manufacturer rolled his own. And of course, back in the dark ages, primitive on-board computers would blink dashboard lights and stuff like that to read out codes. ("Codes" in this context stands for "Engine fault codes" that describe specific failure conditions.)

    It's amazing what data you can get with OBD II: current RPM, speed, status of various systems, temperatures, pressures, flow rates, and voltages in various parts of the engine and drivetrain. Have fun, I hope you're able to get something going.

    -Th

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