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Thread: Problem with 4x4 in 99 GMC Jimmy

  1. #1
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    Problem with 4x4 in 99 GMC Jimmy

    I've got a 99 GMC Jimmy with the 4-botton auto NP8 4x4 system. When I first turn my key forward all of the lights on the 4x4 switch illuminate for ~1 sec then my service 4wd light comes on and the 4x4 system is completely inoperable. I have:

    Verified that all vacuum lines are in tack and properly functioning
    Replaced the in dash 4x4 switch with a new one
    Checked connection on encoder motor
    Checked all fuses
    Unplugged battery for ~8 hours


    I'm thinking that I've either got a bad electrical connection or my Encoder motor or TCCM(transfer case control module) is/are toast.

    I was hoping that someone here may have access to a troubleshooting flow diagram or wiring diagrams for this system. I called my local stealerships to get a price on pulling the codes and the cheapest one was $50. It will really hurt to pay them that much for 5 min of work so I am trying to avoid that.

    If anyone has anything that may help you can email me at mattjw76@comcast.net


    Thanks,
    -Matt

  2. #2
    Blazer at heart
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    Here are some instructions on how to check the TCCM for trouble codes I pulled from the s-series forum

    "1. Position the ignition switch to OFF. Ensure the ignition switch is positioned to OFF for at least 6 seconds.

    2. Connect pin 13 on the data link cable to a vehicle ground source. The data link connector is located in the cab under the instrument panel on the drivers side.

    3. Position the ignition switch to RUN.
    Note the shift select buttons for blinking codes. Refer to Diagnostic Trouble Codes .

    If the shift select buttons all blink one time and stop, and do not continue to blink, no fault codes are stored in the TCCM.
    The transfer case shift select buttons will blink in order to identify any stored DTC. If only one code is stored in the TCCM memory, that code will blink repeatedly with a three second delay between blinking sequences. If more than one code is stored, the first code will blink once, then after a three seconds delay, the next code will blink. This sequence will continue until pin 13 is no longer grounded.

    When reading the diagnostic trouble codes, the number of shift select buttons blinks will indicate the code number.
    ---------------------------------------------------
    Diagnostic Trouble Code (DTC) 1
    When the ignition switch is positioned to RUN the TCCM test to determine if RAM standby Power (maintained battery power) to the TCCM was lost since the ignition was last turned OFF. When power is interrupted on pin C6 of the TCCM, the TCCM stores a loss of RAM standby power.

    Diagnostic Trouble Code (DTC) 2
    During electronic shifting, the TCCM check the motor/encoder for normal operation. If the motor/encoder does not function correctly enough times, the TCCM stores a motor/encoder failure DTC 2.

    Diagnostic Trouble Code (DTC) 3
    The TCCM performs a test each time the electronic-shift motor is turned ON or OFF. If the motor does not function properly the TCCM stores a motor circuit failure DTC 3, and the shift select buttons blink in order to inform the driver of a problem.

    Diagnostic Trouble Code (DTC) 4
    Each time the ignition is turned ON, the TCCM tests the memory, the program, and the internal system in order to ensure that the TCCM is operating properly. If the TCCM detects a fault within the TCCM, the TCCM stores a RAM/ROM memory failure (DTC) 4.

    When the TCCM is running a diagnostic, and a code 4 is displayed by the shift select buttons, replace the TCCM."

    Hope this helps

  3. #3
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    I think I had run accros that somewhere. Its good info but for the 4-button auto NP8 system I'm told you need a GM Tech II tool to pull the codes.. Maybe I will try this anyway just to be sure..

    Thanks,
    -Matt

  4. #4
    Blazer at heart
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    Campbell River B.C.
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    the tech tool does the same thing, only it uses an lcd screen to tell you whats up instead of blinking the light. I believe the book that comes with the blazers and jimmys in the glove box tells you what wires to jump for engine trouble codes and has a breif list of codes and how many light flashes to watch for. I tested mine with a bobby-pin from the fiance. Good luck, ya don't have anything to lose for trying

  5. #5
    Fully Erect Member
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    Connecticut
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    no the ground trick only works on the 3 button trucks. so it going str8 to check 4wd means there is a hard code in the TCCM. Unfortunately unless the fault doesnt happen 40 or so times the code will not reset. I'd have to say 50$ to have it scanned is well worth a 300$ encoder you possibly dont need, even though i've seen it alot. I usually dont see TCCM's go bad unless they've been exposed to water, ie. extreme water damage. After driving through 4 feet of water my Encoder shit the bed, just after engaging 4wd hi.

  6. #6
    Registered User
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    Va Beach, VA
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    Hell I wish I had known this earlier.. I bought a new TCCM and Motor.


    It was stuck in 4wd low and kept blowing fuses. Of course I think the TCCM was shot anyway. I sold it, but aparently it didnt work in that persons vehicle.

    yes I refunded him the money too.

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