Discussion in 'General Chevy & GM Tech Questions' started by braspu, Jun 18, 2009.

  1. braspu

    braspu New Member

    I am having a problem that is driving me nuts. I have a 91 Chevy k1500, 350, 700r4. Neither the Speedo, odometer, nor cruise controls are working. I changed out the inst. cluster and the vss. It does not have a mechanical speed sensor, electric magnetic. I originally thought it was the cluster so I changed that, no good. A few weeks later the service engine light came on, checked for codes and got 24. I than changed the vss. Still nothing. I checked the harness to the vss with a multi meter while the key was in the on position and got a reading from it. Any suggestions or ideas are appreciated.

    Last edited: Jun 18, 2009
  2. 2ToNe04

    2ToNe04 Epic Member 5+ Years 1000 Posts

    you should scan it with the tech 2

    maybe there old codes from the other truck?
  3. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    You probably have a bad DRAC module. Have you checked it? The DRAC converts the analog signal from the speed sensor to a digital signal and sends it to the speedometer.
  4. 5speedsilverado

    5speedsilverado Epic Member 5+ Years 1000 Posts

    what were the codes, and did you fix them?
  5. braspu

    braspu New Member

    No i have not checked the DRAC module. where is it located, and how do i test it? The only code that came up is a 24. I cahnged the vss and it did not fix it. The SES light is still coming on and tripping the code 24.
  6. 5speedsilverado

    5speedsilverado Epic Member 5+ Years 1000 Posts

    check the wires going to the vss their might be a short somewhere
  7. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    Just Google the code number along with Chevy truck 1991
  8. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    I just looked an your truck may have the DRAC / buffer built into the PCM. Mitchell shows the DRAC module for 1992 models but not 1991. The speedo wireing is dependant on wheather you have ABS and also cruise control.
    What I would do is check the signal from the VSS with a volt meter set to read AC volts. What you will see is 0 voltage with the wheels stopped and then increasing AC voltage as the wheels spin. The voltage number is not important here. Once you verify that the voltage increases with wheel speed the next thing is to follow that wire as far as you can checking for damage to the wire. Next see if the signal is getting to the ECM. Check pin A-10 at the ECM. I can't find a wireing diagram of the cruise control. :(
  9. braspu

    braspu New Member

    still having this problem. after looking at the wiring diagram i noticed that the vss goes to the cruise control module than to the fuse than to the c.c. switch. my question is if the c.c. module is bad will it stop the speedo working? and where is the c.c. module located. on the firewall behind the relay cover? how can i test it? thanks for the help
  10. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    The PCM gets the signal first. What I would do is see if the PCM is indeed getting the signal. Easiest way is with a scan tool. If you don't have one then check the VSS signal with a volt meter set to AC voltage at A10. Spin the wheels and the AC voltage should increase.

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