Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Electronic Speedometer ?'s

Discussion in 'The Garage' started by rusty79beast, Sep 19, 2005.

  1. rusty79beast

    rusty79beast Registered Member

    Joined:
    Sep 30, 2002
    Posts:
    64
    Likes Received:
    0
    Location:
    Houghton, MI
    I just purchased another Blazer. This time it's a 1991 and I'm new to the whole electronic speedometer setup. Well first off the speedometer doesn't work, so my question would be what steps would I take in diagnosing the non-working speedometer? Is there a sensor some where? If so how do I check it? I also read in a past column you can somehow check to see if the computer is getting the correct speed signal? How is that done and what does that tell you?

    I couldn't resist the price on this "new" blazer. $1000 dollars with the only major just being the rocker panels and a little over the rear fenders. The A/C even still works. It has 148000 miles on it, but the previous owner says the speedometer just stopped working while he was selling it so who knows! Well I hope someone can help me out!

    Thanks guys :bow:
     
  2. tiger9297

    tiger9297 1/2 ton status

    Joined:
    Jul 23, 2004
    Posts:
    1,205
    Likes Received:
    0
    Location:
    Tupelo, Mississippi
    My speedometer was intermittant and then just quit working on my '90 K5 which, I think, is the first of the electronic speedometers. I replaced the plug on the transmission but that didn't work. It ended up being the printed circuit. I ordered one from LMN but the one they sent me was not for an electronic speedo. I ended up getting pushed for time so I just took it to the dealership and let them fix that problem plus a few other things. Works perfectly now. Good luck, and in my opinion the 90-91's are the best year models. :D
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,978
    Likes Received:
    189
    Location:
    Roy WA
    If you've got cruise and it works, you've just eliminated the VSS on the tranny, and the wiring leading up to the DRAC.

    A scanner hooked up to the ECM will let you see if the VSS is working right, in the case of no/non-working cruise control. You can see the vehicle MPH in the scanner display. If it reads reasonable (tire size/gear changes will throw it off of course) then the VSS is good.

    The DRAC is what interprets the VSS signal and distributes it to ABS, cruise, ECM and Speedo, and although highly unlikely, since each output is a separate wire, it could have issues even if other components work as they should.
     
  4. rusty79beast

    rusty79beast Registered Member

    Joined:
    Sep 30, 2002
    Posts:
    64
    Likes Received:
    0
    Location:
    Houghton, MI
    The cruise control doesn't work, so do I need a scanner to check to see if the vss is working correctly or is there a simpler way to check the vss? If I was going to buy a scanner, how much could I get one for?
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,978
    Likes Received:
    189
    Location:
    Roy WA
    I don't believe there is a simpler way to test VSS. Of course if you have a labscope lying around, you could test it with that. :rolleyes:

    Autozone apparently has scanners that you can use freely, I'd check with them if you have any close by. You just need to drive with it hooked up and on "monitor" and it will indicate MPH. Without VSS signal to the ECM, problems when you let off the gas and are moving may crop up, so that might point you one way or another as well if that is or is not occurring.

    I have an OLD autoxray XP240, but it works fine. I bought mine for about $100 off ebay, it came with cables for Ford and Dodge as well as GM.
     
  6. Leper

    Leper 1/2 ton status

    Joined:
    Feb 18, 2005
    Posts:
    4,437
    Likes Received:
    0
    Location:
    Dallas Baby!!!!
    Make sure the sensor is plugged in and doesn't have a ton of oil all over it. It is located at the rear of the tcase on the slipyoke shaft housing.
     
  7. rusty79beast

    rusty79beast Registered Member

    Joined:
    Sep 30, 2002
    Posts:
    64
    Likes Received:
    0
    Location:
    Houghton, MI
    I have been reading up on the VSS and I have read that it also controls the air/fuel ratio etc. So does this mean if it runs fine/ doesn't stall that it is OK?? I am new to the electronic speedometer, so I want to learn more before I go out and buy a new VSS and find out that it isn't the problem. I guess I could always go to the junk yard and find a used one for cheap. One last question would be that my brother has a 90 silverado but it is a manual transmission, so could I swap that in to see if it worked? Also what years of pickups could I look for a VSS in a junkyard that would work with my 91 K5?

    Thanks guys :bow:
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,978
    Likes Received:
    189
    Location:
    Roy WA
    Actually missing/bad VSS will typically show up on deceleration...idle speed is tied into VSS for that, so it may stall if the VSS isn't working. Other than that, you probably would never know it wasn't working, short of the speedometer, cruise, etc.

    If you find another donor, post up. I pulled one from an S10 t-case, it's not the same. Pulled the VSS connector from a late 80's or early 90's Astro with 700R4, and the connector was the same as my '91 205 VSS. Couldn't get to the sensor to pull it though, didn't even think about it. :doah:

    ACdelco shows two different sensors for that time period, but I can't tell what the difference is. Both seem to have been used in C/K/R/V trucks for quite some time.
     
  9. HarryH3

    HarryH3 1 ton status Author

    Joined:
    May 31, 2000
    Posts:
    10,384
    Likes Received:
    2
    Location:
    Georgetown, TX
    Do yourself a BIG favor and buy a factory shop manual set for the new rig. It has great troubleshooting flow charts for all of the various sensors. You can quickly spend a LOT of cash throwing parts at phantom problems on EFI rigs. A good scanner will also help a bunch. The scanner and manuals will pay for themselves in parts that you don't have to buy. :D
     

Share This Page