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Speedo help.......

J

jester83

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Magna, Utah
I have a 1990 Sub and the speedo and odometer quit working for me. I have tried finding info but cant seem to find exactly what I am looking for.

First off, where is the vss located. I am pretty sure its on the t-case but I havent been able to find it. Also, the button on the dash to reset the trip mileage is stuck. It will not push in. So I am basically trying to narrow it down to whether or not it is the speedo itself that is bad or the vss. Does anyone know how to test the vss?

Any help would be great. Thanks
 
The VSS is located in the T-case on 90 and 91. The connector has two wires and is located on the top rear of the case. The wires lead up to the DRAC module which is mounted on the back side of the lower dash panel about where your right knee is. If you have a multimeter with a "Hz" setting, you can check the output of the VSS or DRAC. Pretty much any frequency reading that goes up and down with vehicle speed indicates a good DRAC. HAve a buddy hold the multimeter while you drive. You hate end up with an old lady or stroller under the front axle 'cause you were watching the meter. Pics of a DRAC and more info on it can be found here.
 
I am assuming he has a 241 T-case. I don't think any subs that late got 205s, but the 90 205 could be mechanical with VSS at the back of the speedo.
 
So from your guys' experience, with my trip reset button being stuck, does it souns more logical that it would be a speedo head problem or a vss or drac problem?
 
The VSS and DRAC are both pretty robust, not a lot to go wrong there. I'd suspect the speedo head myself
 
jester83 said:
So from your guys' experience, with my trip reset button being stuck, does it souns more logical that it would be a speedo head problem or a vss or drac problem?
Click to expand...
My trip meter is stuck too, yet my speedo and odometer work fine. I suggest running the tests like mentioned above.
 
I quit messing with my trip mileage.. it's always off by 10%-20% but the speedo and odometer are both dead on.
 
jester83 said:
So from your guys' experience, with my trip reset button being stuck, does it souns more logical that it would be a speedo head problem or a vss or drac problem?
Click to expand...


AFAIK trip has no bearing on the speedometer/odometer functions. So should be separate. Might as well find a replacement speedo to fix the trip, see if that solves your other issue as well. You can try fixing the trip, but I'd expect them to be a fragile setup and probably already has broken parts.

You can tell if your VSS is working with a scanner. If the ECM is registering vehicle speed while the rear wheels are turning, the VSS/DRAC is working, at least the circuit of the DRAC that is feeding the ECM portion. Two wires off of the DRAC that we are concerned with here, one to the ECM, one to speedo.

Autozones (at least some) will "scan" your vehicle for free.
 
So the weirdest thing happened last night. Just a little background here, my speedo/odo was not working and my brake pressure light has been on and my blower motor has not worked since I have had this suburban. Last night I started digging into the blower motor problem and found what I thought to be a bad blower motor relay. Replaced the relay and it still didnt work. did some hunting and tested fuses and found i missed one of the heater fuses which ended up being bad. replaced it. blower motor worked great. went to bed.

Well I got up for work and started driving when I realized that my brake light was not on anymore and my speedo is now working. Are these somehow tied in with the blower motor relay?

Either way I am happy it works. One less thing I need to fix now :-)
 
My guess is a bad connection got bumped while you were checking other things under the dash.
 
The '90 may have ABS, in which case a bad VSS signal should turn on the brake light in addition to having a dead speedo.

x2 on the "bumped" connection, there should not be a relay in that circuit.
 
I believe it does have abs, looks like an ecu attached to the master cyl.

Whatever happened it is working now so I am happy either way
 
BGKYK5 said:
The '90 may have ABS, in which case a bad VSS signal should turn on the brake light in addition to having a dead speedo.

x2 on the "bumped" connection, there should not be a relay in that circuit.
Click to expand...

IIRC, all 1990-91 R/V trucks had that awful rear-wheel-only ABS; the only one I've personally owned never worked so I just left it disconnected. :dunno:

-- A
 
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