This may be a stupid question, but I'm going nuts trying to find out what is wrong with my speedo and was informed that my check engine/service engine light would be on if my VSS is bad. Does this mean it will be on while the car is running or just when it is started? It's not on when it is running. Also, how do you check your codes? Are codes thrown only when a problem exists? I'd love to see what is going on.

Sorry for all the questions, I just don't want to rule out the VSS until I am sure about this stuff.

 

One more question, are codes only thrown when the check engine/SES light is on?

 

Sorry i'll elaborate. When the computer sense a fault when the car is running, it will throw the code and cause the SES light to come on while running. If the condition goes away, the light will turn off when running but the code will still be stored in the computer, hence when you initially put the key in the ignition to the "ON" position (but don't start it), the SES light will illuminate because the code is still in the computer. To check the codes just get a paper clip or wire and connect the two terminals in the top right hand corner of the ALDL while the engine is off but when ignition is on. The computer will then transmit codes via SES light. It will first flash once, pause, and then flash twice, and do this cycle 3 times (a code 12) to indicate the computer is functioning. After that it will read all the trouble codes in the same fashion 3 times as well, after which it will go back to indicating a code 12 after all codes have been read. The ECM will throw a code if it doesn't getting pulses from the VSS. The VSS, as i explained to you earliers, shares the speed information with the computer as well controlling the speedometer. If the ECM isn't throwing a code, the ECM is getting signals from the VSS and it means theres a lose connection or bad contact somewhere down the line from the buffer in the ecm to the cluster. The ECM is self-centered and doesn't care if the cluster is getting signals from the VSS, and will only throw a code if it isn't getting any info from the VSS. Now if the ECM or the speedo buffer is bad, then it could quite possibly be the VSS as well. I'm no expert but maybe Vader or someone else of higher-car intelligence can chime in...........

 

I can't thank you enough for your help and patience. I'll check to see what codes the comp is throwing. I guess I was so confused because I cannot find a good diagram of the wiring. I figured that if my SES light wasn't on when running that my VSS should be fine and the problem lies between the ECM and the speedo somewhere. I would assume that if my ECM was bad, I'd be experiancing serious problems elswhere, which I am not. Once again, thanks for all your help and I'm just dig around until I find where the problem lies. I know the speedo hasn't worked for a long period of time, so maybe the comp has the codes stored and this will lead me to my problem. I'm starting to wish that it is the VSS and not some hidden wiring problem. I pulled the cluster and all the internal connections look good. No corrosion and nothing disconected. Once again, thank you for your help and patience.