Hello All, you have all been very helpful in the pastso i thought I would toss this question out there as i am getting frusterated with my new blazer AHHH!

I have a 99 blazer 2 dr 4x4 (With the auto4x4 feature)

I was recently driving down the highway when my speedometer seemed to malfunction! My airbag light came on for a few seconds then dissapeared, then my speedometer stopped working. Ever since then, when I am driving it simply JERKS to 45 when accelerating and will jerk to around 100 or so when i am doing highway speeeds, but these are the only speeds it shows, it does not slowly rise as I am accelerating. I pulled the dash and just checked the electrical connections on the harness where it attaches to the guage cluster, it looks alright, cleaned it up a little and put back together but still no go. All of my other guages seem to work okay (Or as okay as they ever did, my gas guage is off... when my low fuel light comes on the needle is below empty and I actually still have a 20-30 liters left in it! any ideas for that one???)

I have heard people talking about the VSS sensor, but i do not know exactly where to find this on the truck nor if it would be the problem. Is there anyway i can find & test the sensor??

Thanks in advance!!

-Bryce

 

i'm not sure if the VSS sensor can be tested, but it is attached to the transmission itself, usually toward the tailshaft end of the trans. it has a nut and a small clamp that holds it in place, and if you remove it you could lose some transmission fluid.

 

does that sound like the vss sensor could be the problem though??

Thanks
Bryce

 

ive never experienced one go bad but i'd think it would have to be either the VSS itself or a computer problem to cause that kind of error.

 

Until the speed can be checked at the PCM, you cannot rule out a failed instrument cluster.

My scan tool can display the speed, among all of the other sensor values that the PCM supports. I wouldn't go replacing anything until you can determine if the PCM is getting the correct signal from the VSS.

 

Take Kyle's advice here, because if the transmission is shifting properly Your PCM is probably getting a good signal from the vss ( vehicle speed is one of the inputs that the PCM uses to determine shift points for the transmission). It sounds like (based on the fact that the motor moves and sticks at certain speeds) the speedometer motor (inside the cluster) is bad, but you need to have it display the vehicle speed on a scan tool to verify the VSS signal is o.k.

 

Hey.. A thought on this just popped into my head. My cousin had a VERY similar situation in his neon (different vehicle I know) with his tach (different part of the cluster I know). His tach would not read anywhere near the right rpm. Sometimes it would be high, and sometimes it would be low. His problem was very simply from the needle not being seated properly onto the instrument stud. It is possible that vibration is allowing the needle to grab on the center stud for just a bit at certain speeds.

I would atleast try to take the cluster out (the battery should be disconnected whenever connecting or disconnecting the cluster). Remove the clear front panel. Remove the speedo needle. Now plug the cluster back in and key on the vehicle (still without the front panel or needle on). Wait until all of the other gauges have come to a rest (don't know if yours sweep through their motion or not), then press on the speedo needle at the zero position. Put the clear front panel back on and take it for a spin.

See if that works. If it works, GREAT! If not, you atleast tried something that only required your time and it's time to look for a replacement cluster.