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code reader for GM

Discussion in 'Misc Electronics' started by Jon G., Nov 1, 2004.

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  1. Jon G.

    Jon G. Guest

    I have a 94 Pontiac Bonneville. The check engine light goes on
    sometimes. At idle, the oil pressure oscillates up and down.
    The check engine light usually goes on after going high speed
    and slowing down to a stop.

    I have tried to find a code reader for it. The connector is
    trapezoid (D-shaped). This is supposed to mean that the
    computer is OBD II, but since the car is a 94, it was during a
    hybrid year and needs a OBD I to OBD II adapter.

    Can anyone tell me a way to read the codes?

  2. Dick C

    Dick C Guest

    « Paul » wrote in
    The problem is that in 94-95 GM used the OBDI system with an OBDII
    connector. Dealers usually have the scanner, but that, of course,
    costs alot of money just to have the codes read.

    Dick #1349
    "They that can give up essential liberty to obtain a little temporary
    safety deserve neither liberty nor safety."
    ~Benjamin Franklin

    Home Page:
  3. Jon G.

    Jon G. Guest


    thanks for your help all.

    My OBD II connector has pins 4,5,8,9,14,16 populated. This
    doesn't match *any* of the standard configurations for OBD II
    scanners (there are 4 protocols). From what I can determine,
    the pinouts are,

    pin 4 chassis ground
    pin 5 signal ground
    pin 8 ?
    pin 9 signal ?
    pin 14 CAN Low (J-2284)
    pin 16 battery power

    Then someone wrote,

    "Yes, some OBD-II equipped vehicles have a hybrid system where
    the PCM is OBDII and the other modules in the vehicle are
    pre-OBDII, 8192 baud UART. The vehicle will typically have a PIM
    (Powertrain Interface Module) that converts the OBDII to 8192
    UART and back again to facilitate comms between the two
    different systems.

    The OBD-II connector uses pin 9 to provide access to the 8192
    UART data of the non-OBDII modules."

    Can I jump 2 of the pins for a flashing Check Engine light code
    readout? If so, which ones?
  4. Dick C

    Dick C Guest

    « Paul » wrote in
    Late 94 I think.

    Dick #1349
    "They that can give up essential liberty to obtain a little temporary
    safety deserve neither liberty nor safety."
    ~Benjamin Franklin

    Home Page:
  5. Jon G.

    Jon G. Guest

    If it's OBD I, you can jump two of the pins. Under the hood it
    says the car is OBD I compliant, but under the dash it has and
    OBD II connector.

    the female looks like,

    \ 1 2 3 4 5 6 7 8 /
    \ 9 10 11 12 13 14 15 16 /

    the following pins are populated:

    pin 4 solid black
    pin 5 black with white stripe
    pin 8 black with white stripe
    pin 9 tan
    pin 14 green
    pin 16 orange

    compare this with the OBM II protocols:

    J1850 VPW pins 2,4,5 and 16
    ISO 9141 pins 4,5,7,15 and 16
    J1850 PWM pins 2,4,5,10 and 16

    Short-circuiting pin 4 and 15 of an SAE J1962 connector for 3
    sec gets the check engine blinking.

    The pin configuration on my car doesn't match any of the OBD II
    scanner protocols. Will a code scanner still work? If the car
    is and OBD I with an OBD II connector, then which pins do I jump
    to pull a code from the blinking check engine light?

  6. Ken Weitzel

    Ken Weitzel Guest


    Dunno if it'll help to clarify things a bit, or just
    muddy the waters more, but...

    Mine is the 12 pin system. (and I have a mickey mouse
    reader for it). The pins are lettered (opposed to numbered)
    and according to the book that came with the reader A is ground.
    B is the diagnostic test terminal. Shorting A and B
    causes the check light to flash the codes.

    My Haynes book says for the 12 bit type I need only
    short A + B... and it works... but for the 16 bit type
    I would need a reader.

  7. Jon G.

    Jon G. Guest

    Hi Jeff &

    I think the idea was to use an OBDII scanner to read the OBDI
    system, since OBDII scanners often read OBDI as well. I don't
    know this for sure. Under the hood the car is labeled as OBDI
    compliant, so likely it's OBDI with an OBDII connector. If this
    is the case, your Actron OBDI reader would work on my 94
    Bonneville as well. Thank you for your insight.

    I have a friend who has an OBDI reader. Maybe all I need is the
    adapter cable. I could do without the reader or cable if I only
    knew what the OBDII connector wires/pins, correspond to the OBDI
    connector, and jump a couple of them for a flashing check engine
    light code readout.
  8. Jon G.

    Jon G. Guest

    Something's going on here.

    If I buy and Actron OBDI reader, complete with OBDI and OBDII
    cables, then I could map how the OBDI reader converts to OBDII
    pinouts, with an ohm meter, testing continuity between either
    ends of the cable for each pin, and then correllating.

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