Thread: Anyone ever wire an OBD2 device directly to PCM?

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  1. #1 Anyone ever wire an OBD2 device directly to PCM? 
    GTX Level Member industrialfish's Avatar
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    There is only one data wire. Can I just bypass all the harnesses and just connect directly to the connector at the PCM? I mean it works on an offboard tuner with no problems right?
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  2. #2 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    it does on a off board. what you trying to do add a extra obd2 port? they sell spliters for that.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  3. #3 Re: Anyone ever wire an OBD2 device directly to PCM? 
    GTX Level Member industrialfish's Avatar
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    Quote Originally Posted by Scottydoggs View Post
    it does on a off board. what you trying to do add a extra obd2 port? they sell spliters for that.
    Yeah I made an offboard for my DHP since it wouldn't connect through the OBD port. Was thinking of wiring my Aeroforce gauges in so the port is open if I need to plug in DHP or AutoTap for logging.
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  4. #4 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    you might be able to rig something like that up, just need to read the pcm pin out thread and splice away .

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  5. #5 Re: Anyone ever wire an OBD2 device directly to PCM? 
    GTX Level Member industrialfish's Avatar
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    I'm going to try it anyway, was wondering if anyone else had done it before and had success.
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  6. #6 Re: Anyone ever wire an OBD2 device directly to PCM? 
    SE Level Member Casper00693's Avatar
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    Im planning on doing this myself since my car wont read pcm for ****.
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  7. #7 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    Quote Originally Posted by Casper00693 View Post
    Im planning on doing this myself since my car wont read pcm for ****.
    if you got a 04 up pull th eradio fuse before reading or writing to it.

    or you can build a off board tuner rig, it bypasses the car and feeds right to the pcm.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  8. #8 Re: Anyone ever wire an OBD2 device directly to PCM? 
    SE Level Member Casper00693's Avatar
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    Bought this 99 GT, car sat for 4yrs almost, i tuned it before it sat and other stuff, now though... Wont do nothing i got the dhp to read codes but reading/writing no go, actually fried a Pcm already and now the car is back to doing nothing. I need to scan and tune since i just top swapped it as soon as i got it.

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    Xp cam as soon as i close on my house so i really need to scan this.

    When you say offboard that sounds to me like removing the pcm and i cant scan that way, if so explain cause i have all the pin outs for the plugs already, found them on this page too
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  9. #9 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    the off board is for reading and writing only. you need to remove it or just unplug it and flash to it in the engine bay. how i do 04 up's. you can pull the one blue plug off and plug in there.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  10. #10 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    you tey a fresh install of dhp? got the dotnet driver installed?

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  11. #11 Re: Anyone ever wire an OBD2 device directly to PCM? 
    SE Level Member Casper00693's Avatar
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    Been tuning for 6
    7+yrs, its the car lol. I have to take the pcm out install in my Daytona to tune it again. I cant scan something that doesn't read so the offboard isn't any help.
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  12. #12 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    you got another car you can run dhp on? you know to test the unit out with.

    with a off board you can scan but its all dead info, like the cars not running, but it will show everything your scanning and values. that would narrow it down to the cars wiring or the pcm being bad.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  13. #13 Re: Anyone ever wire an OBD2 device directly to PCM? 
    SE Level Member Casper00693's Avatar
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    Reading threw my replys top fast Scotty.

    Offboard isn't an option, vehicle needs scanned, id have to drop thw engine in another car to scan it...

    Another point... Emissions cannot use an offboard to check for codes. Lol

    1 wire... Why not just cut the damn thing and re-run it.
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  14. #14 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    you lost me. i suggest re reading my last post lol

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  15. #15 Re: Anyone ever wire an OBD2 device directly to PCM? 
    SE Level Member Casper00693's Avatar
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    "with a off board you can scan but its all dead info, like the cars not running, but it will show everything your scanning and values"

    So you cannot scan? You're saying you can scan but itll be like cars off so technically you cant scan.

    U asked if i had another car to test i replied earlier that yes i had to use my Daytona500 to tune the top swap.

    I need the obd2 port to work for inspections AND to scan and tune again this is going to be a build car why an offboard is ruled out as not an option at all, whats the point in having an offboard when you can't scan the car with it?
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  16. #16 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    Quote Originally Posted by Scottydoggs View Post

    with a off board you can scan but its all dead info, like the cars not running, but it will show everything your scanning and values. that would narrow it down to the cars wiring or the pcm being bad.


    this part you didnt quote.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  17. #17 Re: Anyone ever wire an OBD2 device directly to PCM? 
    SE Level Member Casper00693's Avatar
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    Poor OP is probably thinking the same thing as I. Offboard is irrelevant in this post. Offboard has nothing to do with the OP question nor mine. Nor does an offboard make any sense to the questions and the clearity of what is being said. Even your replys are useless and have no understanding from what is being said.

    Can an offboard scan a running car? No.

    Can u use an offboard for inspection? NO

    Can you scan and tune a car with an offboard? No.

    Can you use an offboard to tune? Yes, if you remove the pcm.

    Does an offboard have anything to do with this topic? Yes and No.

    Scotty what the hell are you talking about or not understand? We can help you but not really based off your replys no matter how many times its been explained you still say... "I don't get it".
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  18. #18 Re: Anyone ever wire an OBD2 device directly to PCM? 
    Killa Bee Scottydoggs's Avatar
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    what the hell are you not following here. you reading a second language here?

    you dont know why the hell your car cant read or be written to, or scanned. you need to figure out if its the pcm or the cars wire harness, im just saying a off board would rule out the pcm being bad. and lead you to fix the car side of things or get a new pcm for it. re reading my own crap thats been made clear.

    sorry your not following my words.

    so if you go back and re read my posts maybe you can make sense of it now. if not, to bad i guess.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  19. #19 Re: Anyone ever wire an OBD2 device directly to PCM? 
    GXP Level Member Turbocharged400sbc's Avatar
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    check for power and ground at the DLC, dont jam the multimeter prongs into the terminals! once thats confirmed as good you can use the ACv seting to check the serial data line for a signal.

    more than a few times with older vehicles ive found weak terminals that have intermittent/no connection....the DLC is quite common as it's used all the time and many people wiggle the connector up and down instead of left and right to install/remove the plug. all flat pin connectors should be wiggled parallel to the flat pins orientation.

    it could be as simple as using a sewing needle to slip under the banana spring and re tighten it.

    also after major work double check that all your engine/pcm block grounds are good. dont forget the unibody ground on top of the unibody frame rail below the battery or pcm dep on model/year.
    the bellhousing stud should have a tan and a black wire to one ring terminal and usually another pair of black or black with a white tracer stacked with it and the main batt ground cable.


    i have had schmegged pcm's cause no serial data. so an offboard/standalone setup would help diagnose that one....you will be able to scan/read the pcm, but the data pids will be default values/open circuit voltage.

    if you leave the pcm in the car and only unplug the blue connector and insert the offboard blue conn, you will be able to see the data for the sensors/etc it gets from thhe car on the clear connector you left plugged in....this will let you see PCM voltage and double check it has no voltage drop vs the multimeter batery voltage reading.

    also be aware the serial data wire runs through the harness above the radiator and more than a few times ive found wires rubbed through/shorted to ground from dogbone bracket/radiator services.

    also check the pcm/etc fuses and loock for corrosion in the fuse block
    checking the obd2 dlc connector - YouTube
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