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TECH GM OBDII Operating parameters
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  1. #1
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    GM OBDII Operating parameters

    I have been trying to sort out a trouble code on my truck, in the search I found this GM site. For those that dive into such, this gives more info than most "code reader" references.

    OBDII is an industry standard now, this information will apply to other brands.


    http://service.gm.com/gmspo/mode6/index.html
    Last edited by Millwright; 08-07-2013 at 08:03 AM.
    Proud Infidel...............and Cracker

  2. #2
    No link?
    Please visit my video blog www.3MinuteDaily.com

  3. #3
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    Fixed.

    Thanks IG
    Proud Infidel...............and Cracker

  4. #4
    Join Date
    Mar 2011
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    Birthplace of the Texas Flag
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    Great, thanks. I was getting a code P0442, EVAP SYSTEM, Small Leak Detected. No clue as to what it really was.
    This tells me a little more if I decide I want to trace it down. Probably won't, but good to know.

  5. #5
    Good link, I carry my OBDII with me every day for one of my business' and this will come in handy.
    Please visit my video blog www.3MinuteDaily.com

  6. #6
    Join Date
    May 2001
    Location
    Cleveland OH looking towards TX wistfully
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    Quote Originally Posted by Papacub View Post
    Great, thanks. I was getting a code P0442, EVAP SYSTEM, Small Leak Detected. No clue as to what it really was.
    This tells me a little more if I decide I want to trace it down. Probably won't, but good to know.
    My VIBE (GM/TOYOTA) had that code...2 solenoids and 800 bux later it's good to go (which is REALLY good since I need to get AIM'd today or tomorrow as it renews tomorrow...and we have the emissions test requirement here in "The Dirty"... and an OBDII fail means no tags....)
    I would STILL rather fight an insurgency (from EITHER SIDE) than an epidemic!

    "I must not fear.
    Fear is the mind-killer.
    Fear is the little-death that brings total obliteration.
    I will face my fear.
    I will permit it to pass over me and through me.
    And when it has gone past I will turn the inner eye to see its path.
    Where the fear has gone there will be nothing....only I will remain"

    Frank Herbert "Dune" "Bene Gesserit Anti-Fear Litany"


    http://bluemudpatriot.wordpress.com/

  7. #7
    Join Date
    Jan 2013
    Location
    Missouri Ozarks
    Posts
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    DTC 442 is a non driveability code issue. EPA only! Gas caps loose cause most of these codes in our shop, old dry or cracked seals around the gas cap will also contribute. However if you live on dirt roads the evap vent valve on most GM cars sits up under the body near the back of the car (stupid placement) it catches all the dust as you drive down the road. The vent valve is normally open allowing fresh air to come into the tank with vaccum sucking the gas fumes into the intake. All of our Ozark dirt roads kill these sensitive little vent valves. It is a constant issue hear in Dirt Road America!

    This code and its sisters codes will not change any performance or fuel mileage until you can get it into a reputable shop to have it fixed costs can range from $75 to $300.

    Good luck, but don't loose any sweat about it or bust your monthly budget for it. Plan and budget for the repair if you are tight on resources

  8. #8
    Always good to have a reader. I bought an inexpensive $50 reader from Harbor Freight works well very pleased with it.

  9. #9
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    Location
    Cleveland OH looking towards TX wistfully
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    Quote Originally Posted by LYKURGOS View Post
    DTC 442 is a non driveability code issue. EPA only! Gas caps loose cause most of these codes in our shop, old dry or cracked seals around the gas cap will also contribute. However if you live on dirt roads the evap vent valve on most GM cars sits up under the body near the back of the car (stupid placement) it catches all the dust as you drive down the road. The vent valve is normally open allowing fresh air to come into the tank with vaccum sucking the gas fumes into the intake. All of our Ozark dirt roads kill these sensitive little vent valves. It is a constant issue hear in Dirt Road America!

    This code and its sisters codes will not change any performance or fuel mileage until you can get it into a reputable shop to have it fixed costs can range from $75 to $300.

    Good luck, but don't loose any sweat about it or bust your monthly budget for it. Plan and budget for the repair if you are tight on resources
    Yup. MY repair shop told me it was only an AIM/EPA thing...but license renewal coming up and for this car I need the code to be gone.....
    I would STILL rather fight an insurgency (from EITHER SIDE) than an epidemic!

    "I must not fear.
    Fear is the mind-killer.
    Fear is the little-death that brings total obliteration.
    I will face my fear.
    I will permit it to pass over me and through me.
    And when it has gone past I will turn the inner eye to see its path.
    Where the fear has gone there will be nothing....only I will remain"

    Frank Herbert "Dune" "Bene Gesserit Anti-Fear Litany"


    http://bluemudpatriot.wordpress.com/

  10. #10
    Join Date
    Sep 2012
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    Commiefornia
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    861
    With any EVAP SYSTEM codes...Step one, check your gas cap for being tight..this can cost you $$$ if your mechanic is a douche bag rip off artist.

  11. #11
    Quote Originally Posted by subnet View Post
    With any EVAP SYSTEM codes...Step one, check your gas cap for being tight..this can cost you $$$ if your mechanic is a douche bag rip off artist.
    Yep

    and

    Always check your radiator cap is holding it's pressure, first, before you authorize cooling system repairs

  12. #12
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    Jan 2013
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    Missouri Ozarks
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    25
    What year Pickup are you driving I have a cheaper work around for some years.

  13. #13
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    May 2001
    Posts
    12,195
    If you purchase a scanner, be sure to purchase one that is capable of reading livestream data. (Hint: code-only cheapie 'scanners' can't.) The reason: OBD-II DTCs (Diagnostic Trouble Codes) will only tell you what sensor or system is reporting a problem, but not necessarily what the problem actually is.

    For example, seeing a P0171 or P0174 (which are "bank 1 oxygen sensor/system too lean" or 'bank 2 oxygen sensor/system too lean," respectively) usually prompts the reaction "replace an oxygen sensor." However, the oxygen sensor(s) might be picking up something else. By looking at the livestream data, you can see what the oxygen sensors are doing, and if you see both P0171 and P0174 and your long-term fuel trims are strongly positive (15+%) but the upstream oxygen sensors are switching like they should (0.0-1.0VDC, switching rapidly) and the downstream sensors are tracking accordingly (0.0-1.0VDC, slowly following the upstreams like a rolling average), you've got a vacuum leak somewhere, not bad sensors. If there's also a P0300 ("random misfire"), it's a really bad vacuum leak (e.g., intake gasket failure). Otherwise, check for things like collapsed rubber PCV elbows, broken vacuum lines, etc.

    A modern car's engine management system operates on a giant feedback loop, where the MAF/MAP/AIT sensors tell the powetrain computer what's coming in, the TPS tells it what the engine is being told to do by the driver, and the oxygen sensors monitor catalytic converter performance and detect the backside results from air/fuel combustion. Understanding how the system works, and being able to inspect what each sensor is reporting while the vehicle is running, are critical keys to finding and fixing problems.
    IMPORTANT NOTE: Any religion-related posts I make are as a member and not as a forum staffer, and are not intended to promote any specific agenda or doctrinal understanding as official or unofficial board policy. Official staff actions on my part will always be clearly marked as such.

    Deja moo - the feeling you've seen this bull before...

    "Political Correctness is a doctrine fostered by a delusional, illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

  14. #14
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    Quote Originally Posted by Double_A View Post
    Yep

    and

    Always check your radiator cap is holding it's pressure, first, before you authorize cooling system repairs
    First thing my brother (who owns an auto repair shop) does when there's a cooling system issue is inspect and pressure-test the radiator cap. If it passes, he pressurizes the cooling system proper and hunts for leaks. He has a car in his shop right now that blew its head gaskets because the owner drove it for over a year with a bad radiator cap and it pushed out all the coolant.
    IMPORTANT NOTE: Any religion-related posts I make are as a member and not as a forum staffer, and are not intended to promote any specific agenda or doctrinal understanding as official or unofficial board policy. Official staff actions on my part will always be clearly marked as such.

    Deja moo - the feeling you've seen this bull before...

    "Political Correctness is a doctrine fostered by a delusional, illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

  15. #15
    Join Date
    May 2001
    Posts
    12,195
    BTW, if your vehicle is even close to modern - and basically this applies to anything fuel-injected - DO NOT OVERFILL YOUR TANK. When the pump kicks off, you're done - DO NOT try to add enough gas to round off the price. If you overfill the tank you'll dump liquid gas down the purge vent line and destroy the emissions control canister (which is full of activated charcoal) and purge control solenoid, which are designed for fuel vapors only and cannot handle liquid fuel at all. This can cost anywhere from a couple hundred dollars to a grand or more to fix depending on the vehicle, and if left unchecked the trouble codes from this can and will hide codes for other/larger issues.

    Also, don't gas up with the engine running. Many autos will throw a P0445 if you do. Should be a "duh" type thing but people do it all the time.
    IMPORTANT NOTE: Any religion-related posts I make are as a member and not as a forum staffer, and are not intended to promote any specific agenda or doctrinal understanding as official or unofficial board policy. Official staff actions on my part will always be clearly marked as such.

    Deja moo - the feeling you've seen this bull before...

    "Political Correctness is a doctrine fostered by a delusional, illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

  16. #16
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    I will run mine in monitor mode from time to time while going down the road. This gives an idea of what values to expect for different sensors. I tend to remember these things.......don't know anybody's birthdays in my family, but know the normal fuel rail pressure for my truck.

    The scanner I bought is an Actron autoscanner plus, they offer online support to update the scanner for current car models, not a top-shelf unit but adequate.

    Having the ability to access the computer in your vehicle is huge, not often, but when you need it, it's critical.

    This winter we were working a snowstorm here in OK, towing and fueling generators. I got sloppy on I-40 way out west and slid off the shoulder in knee deep snow. I had to shut down the freeway for a minute to drag me out when some of our other guys came along. In trying to get out I did something that upset my tranny (Allison/Duramax), as I was going to the next town noticed that RPMs were a little high. When I got off the highway and stopped, I barely made it through the intersection (OH CHIT! moment), limped into a parking lot, crawled under to look for wires pulled loose or such....no luck, it would barely move. After trying all the obvious things I plugged in the scanner, it gave some funky pressure/sensor code. I cleared the code to see if it would repeat when I tried to go, that fixed it, whatever happened was a transient problem and it has been going down the road without a hiccup.

    I would advise everyone to get some kind of scanner and play with it on your BOV a little bit. Having a basic working knowledge may save your bacon one day.
    Most car computers have a "limp home" mode that covers most sensor failures, if any given sensor gives an output that falls outside normal operating parameters the computer takes all the other data and substitutes values for that sensor, that will get you down the road. It will not let the motor hurt itself (high temp, lean burn, high RPM, etc.). When you are in limp home mode you have reduced power and may only be able to go 35mph but........You aint drivin' the Pats & Benz (Pats dem feets and Benz dem knees). Having the ability to delete trouble codes may buy you a few miles at full power.

    If you don't have time or ability to troubleshoot & repair your own vehicle, when you bring it to a shop and tell them "it is giving me xxxx code, I think it is YYYY sensor", they are not as likely to try to sell you a special Kneuter valve rebuild kit with the unobtainium lining. There IS a forum like TB for your vehicle, use it to get an idea of what your malfunction is, I promise somebody has been there and is willing to share info. Search for camry forum or chevy truck forum or whatever applies to you.

    Here on TB is a wonderful knowledge base, the more info you can give on an automotive problem, the more likely someone here will be able to give an accurate fix.
    Last edited by Millwright; 08-07-2013 at 11:58 PM. Reason: YEAH.....What Odd One said.
    Proud Infidel...............and Cracker

  17. #17
    Quote Originally Posted by OddOne View Post
    If you purchase a scanner, be sure to purchase one that is capable of reading livestream data. (Hint: code-only cheapie 'scanners' can't.) The reason: OBD-II DTCs (Diagnostic Trouble Codes) will only tell you what sensor or system is reporting a problem, but not necessarily what the problem actually is.

    For example, seeing a P0171 or P0174 (which are "bank 1 oxygen sensor/system too lean" or 'bank 2 oxygen sensor/system too lean," respectively) usually prompts the reaction "replace an oxygen sensor." However, the oxygen sensor(s) might be picking up something else. By looking at the livestream data, you can see what the oxygen sensors are doing, and if you see both P0171 and P0174 and your long-term fuel trims are strongly positive (15+%) but the upstream oxygen sensors are switching like they should (0.0-1.0VDC, switching rapidly) and the downstream sensors are tracking accordingly (0.0-1.0VDC, slowly following the upstreams like a rolling average), you've got a vacuum leak somewhere, not bad sensors. If there's also a P0300 ("random misfire"), it's a really bad vacuum leak (e.g., intake gasket failure). Otherwise, check for things like collapsed rubber PCV elbows, broken vacuum lines, etc.

    A modern car's engine management system operates on a giant feedback loop, where the MAF/MAP/AIT sensors tell the powetrain computer what's coming in, the TPS tells it what the engine is being told to do by the driver, and the oxygen sensors monitor catalytic converter performance and detect the backside results from air/fuel combustion. Understanding how the system works, and being able to inspect what each sensor is reporting while the vehicle is running, are critical keys to finding and fixing problems.
    That's all true and good if you can afford a several hundred dollar unit.

    I for one decided not to, I just wanted to know two things from that idot light that came on, 1) what is the proper direction to start looking as the light gives you NO info and 2) when I take the vehicle in the shop and the mechanic says you have problems here, here and here and it's gonna be expensive, I can catch him in a lie.

  18. #18
    Join Date
    May 2001
    Posts
    12,195
    Quote Originally Posted by Double_A View Post
    That's all true and good if you can afford a several hundred dollar unit.

    I for one decided not to, I just wanted to know two things from that idot light that came on, 1) what is the proper direction to start looking as the light gives you NO info and 2) when I take the vehicle in the shop and the mechanic says you have problems here, here and here and it's gonna be expensive, I can catch him in a lie.
    Actually, sub-$300 scanners exist that can read livestream data. For example, AutoZone lists one for $140 that supposedly supports all OBD-II scan modes and displays livestream info on a LCD screen. (Linky)

    And I agree with you on the usefulness of having your own code reader when it comes to catching unscrupulous shops.
    IMPORTANT NOTE: Any religion-related posts I make are as a member and not as a forum staffer, and are not intended to promote any specific agenda or doctrinal understanding as official or unofficial board policy. Official staff actions on my part will always be clearly marked as such.

    Deja moo - the feeling you've seen this bull before...

    "Political Correctness is a doctrine fostered by a delusional, illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

  19. #19
    Join Date
    Feb 2002
    Posts
    22,359
    Yeah, but what do you do when you take it to the shop, TELL HIM it has a major gas line leak, and he claims he "smoke tested it" and there's no gas leak- just an EGR valve to replace?

    Replaced the valve... put a 10 day inspection on it, and it's STILL pouring gas out! I can smell it from 10 feet away. In the meantime, we've driven over 200 miles and the codes still haven't cleared... I HATE COMPUTERS ON VEHICLES!!!

    Summerthyme (and I HATE moron mechanics... and these days, it seems they're the only kind out there)

  20. #20
    Ditto what Subnet said about gas caps. Happened to me too.

    Now I've got a check engine light on my 2004 Tacoma. Autozone read it for me as a first oxygen sensor. I've ordered a basic code reader so I can diagnose things myself.

  21. #21
    Join Date
    Mar 2011
    Location
    Birthplace of the Texas Flag
    Posts
    190
    Quote Originally Posted by OddOne View Post
    BTW, if your vehicle is even close to modern - and basically this applies to anything fuel-injected - DO NOT OVERFILL YOUR TANK. When the pump kicks off, you're done - DO NOT try to add enough gas to round off the price. If you overfill the tank you'll dump liquid gas down the purge vent line and destroy the emissions control canister (which is full of activated charcoal) and purge control solenoid, which are designed for fuel vapors only and cannot handle liquid fuel at all. This can cost anywhere from a couple hundred dollars to a grand or more to fix depending on the vehicle, and if left unchecked the trouble codes from this can and will hide codes for other/larger issues.

    Also, don't gas up with the engine running. Many autos will throw a P0445 if you do. Should be a "duh" type thing but people do it all the time.
    I know this to be true on my 2004 Suburban, always put a little extra in when filling up. Had to replace the solinoid and what a pain to get to! Needless to say, I don't do that anymore with any of my vehicles! Also, I've found Rock Auto to be the best place to buy parts.

  22. #22
    Join Date
    May 2001
    Posts
    12,195
    Ah, Rock Auto... Bro gets so many parts from there for vehicles where the customer doesn't mind not having a labor warranty in exchange for reduced part prices...

    (They're a great resource for DIYers since they carry both OEM and aftermarket parts, and their prices aren't ridiculous.)
    IMPORTANT NOTE: Any religion-related posts I make are as a member and not as a forum staffer, and are not intended to promote any specific agenda or doctrinal understanding as official or unofficial board policy. Official staff actions on my part will always be clearly marked as such.

    Deja moo - the feeling you've seen this bull before...

    "Political Correctness is a doctrine fostered by a delusional, illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

  23. #23
    Join Date
    May 2001
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    12,195
    Quote Originally Posted by summerthyme View Post
    Yeah, but what do you do when you take it to the shop, TELL HIM it has a major gas line leak, and he claims he "smoke tested it" and there's no gas leak- just an EGR valve to replace?

    Replaced the valve... put a 10 day inspection on it, and it's STILL pouring gas out! I can smell it from 10 feet away. In the meantime, we've driven over 200 miles and the codes still haven't cleared... I HATE COMPUTERS ON VEHICLES!!!

    Summerthyme (and I HATE moron mechanics... and these days, it seems they're the only kind out there)
    Codes often won't clear on their own once set, and have to be deliberately cleared. (Some codes do, once the computer fails to see the same problem for a certain number of drive cycles, but generally speaking, once a code is set it stays.)

    As for the fuel leak, that should be pretty easy to find if it's that smelly. What's the MMY of the vehicle?
    IMPORTANT NOTE: Any religion-related posts I make are as a member and not as a forum staffer, and are not intended to promote any specific agenda or doctrinal understanding as official or unofficial board policy. Official staff actions on my part will always be clearly marked as such.

    Deja moo - the feeling you've seen this bull before...

    "Political Correctness is a doctrine fostered by a delusional, illogical, liberal minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end."

  24. #24
    Join Date
    Feb 2002
    Posts
    22,359
    2001 GMC Sierra 4wd pickup. It's only got about 80k on it, but it's been used as a farm truck since we bought it new. I wasn't clear- the codes HAVE been cleared.. it's just taking forever for it to reset and go through the whole "drive cycle".

    We're hoping that somehow (God knows how) the check engine light won't go back on, and it will finally pass inspection. THEN we'll take it to a friend who does good work (but doesn't have his license, etc to do inspections) and get him to fix the damned gas leak. I REALLY can't believe the moron who worked on it claims it doesn't have a leak... supposedly, the EGR (might be the wrong term.... we also replaced all the O2 sensors) valve he replaced is nearly on top of the leaking gas lines. We know what line is leaking... second son, who has worked for GM, showed us exactly where it's leaking. It's just such a PITA to get to, we don't want to try to fix it ourselves (with hubby needing a hip replacement immediately, a lot of stuff we'd normally do isn't getting done by us right now- but this repair looks like one I wouldn't want to try without a lift...)

    Summerthyme

  25. #25
    Depending on the code it could take up to 80 drive cycles. To clear on it's own. As long as the repair did fix it.

  26. #26
    Join Date
    Feb 2002
    Posts
    22,359
    Man, I hope not!! Given that a "drive cycle" is between 50-100 miles, it might get done by 2017... (we don't drive much!)

    Summerthyme

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