GM Truck Club
Founded in 2004 ~ We're the #1 Chevy Truck & SUV Forum.
Silverado & Sierra | Tahoe & Yukon | Suburban & Yukon XL | SUV & CROSSOVER
Results 1 to 7 of 7
  1. #1

    Default check engine light, but no codes

    1994 Sub k2500 454

    check eng light comes on, plug in no codes are stored. running or long term.
    Send clear codes command light goes out but not for long.
    Any Ideas??????

  2. #2


    which code reader
    some r more sensiitve than others
    did you config the scanner with the right vehicle ,engine make and model , it matters :}
    some codes on some of my code reader`s will not come up unless u r driving down the road
    and usually if the code reader does not connect to truck`s computer it has to do with the ecm/pcm not working right not getting power {fuse?} and or broken wire and if the broken wire has been shorting out it could be the computer on vehicle

  3. #3


    OTC pro tool

    I can view all data streams

    I suspect ecu failure as well.......

  4. #4


    I don't know about the '94 Sub, but my '05 Envoy would light the CEL when there were codes that were not related to the PCM.

    A lot of scanners will only read Pnnnn codes (P for PCM), codes for ABS, BCM, Traction control, etc are there but can not be read by most scanners.

    You may need a GM TECH II tool to read the code.

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  5. #5


    X2 what RayVoy said, there are several other computers on your vehicle besides the ecm. I use an old Snap On mt2500, and it scans abs, bcm, airbag, tcm, and ecm
    2004 Chevy Colorado 2wd/4l60e/3.5 Inline 5
    6-PIAA 520 series yellow ion spot lights 85 watts each
    PIAA quattro fog lights w/extreme white/yellow ion bulbs
    Anzo projector headlights/LED turn signals
    LED underbodys 7-color/LED interior lighting
    JET stage 2 performance chip/Magnaflow exhaust S/S
    Recon Big Rig Lights/LED tail lights/3rd brake light
    Putco LED bed lights/BEDRUG
    Goodmark 2" rise Cowl hood/K&N fipk intake
    98-04' Blazer overhead console & floor console
    40/60/40 seat modified to 40/console/40
    33" Cooper Discovery A/T
    16" Pro Comp extreme alloy wheels

  6. #6


    Certainly do not a tech II tool for a '94 ........
    I have an OTC scan pro 3499 and it covers ABS and anything this antique i am asking about has on board.
    There is no BCM on this old of a vehicle, and body modules is about all this tool wont read
    Trans control is in the ECU in this vehicle

  7. #7


    Of course, sorry to mislead. So, perhaps a problem with the ECU. Can you reset the ECU, with the scan tool, or by disconnecting the battery?

    After that, if still on, I'd suggest a ground on the lamp lead going to the ECU. I don't have a '94 wiring diagram, but a lot of times, GM will provide battery on one side of the lamp (a lot of the lamps, not just the ECU) and a switched ground on the other side.

    The ECU would (I'm just assuming here) ground the lamp lead when there is a code.

    The reason for the switched ground, is to provide a warning lamp if the switch fails; if the hot side was switched, a switch failure could cause the fuse to blow, or a fire.

Similar Threads

  1. OBDII codes disappeared :-) - Check engine light gone
    By PantheraUncia in forum Chevy Truck Talk & GM News
    Replies: 2
    Last: 04-10-2012, 12:21 PM
  2. Service light v.s check engine light
    By redbone in forum Chevy C/K Truck Forum
    Replies: 1
    Last: 07-21-2011, 11:04 AM
  3. S-10 check engine codes
    By RATRODKING in forum General Chevy & GM Tech Questions
    Replies: 2
    Last: 09-13-2010, 02:33 PM
  4. 04 chevy 2500 diesel engine light codes?
    By bonesandchicken in forum General Chevy & GM Tech Questions
    Replies: 0
    Last: 11-21-2009, 02:07 AM
  5. check engine light
    By Whits96 in forum General Chevy & GM Tech Questions
    Replies: 6
    Last: 01-20-2009, 12:50 AM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts