Thread: Vss reporting 1 mph while in park.

I cant say I've looked at what HPT says, but I do know that I sometimes see the HUD play catch up with the real speed. I can be going 20-25 mph and the HUD is at 18-19 and then it shoots up to 29ish and drops to my speed, but it happens so fast and like I said, it wont happen very often.

This is not too common to see but I have seen it before. If recent repair has been done I would make sure the grounds are all in tact and tight. Interference can cause the signal to twitch a bit at idle also so make sure the wires are all secured as they should be and sounds like you have already looked over the vss wires. An ohm test on the wires from the vss connector to the pcm connector will verify they are both tact and also check them to ground to make sure one isnt rubbing and causing noise in the signal. Noise on the datastream could cause this also and may be the case since your dash reads zero and hpt shows just above this. Do you have a power inverter hooked up to the car through your laptop when watching this or just using it off of the laptop battery? The dash gets its signal via datastream also so I would suspect noise or interferance between the cable and the laptop especially if your hud shows zero and scanner shows 1-3 at the same time.

I would assume he is just going off laptop battery, its not a good idea to run the laptop off the 12v power source while tuning the car. Which anyone with a tuner should know because its in the direction on HPT and posted on the site lol.

Ok no inverter. Nothing wrong with using one to scan- tuning is another story and yes should be common knowledge to not use one to avoid problems but tuning and scanning are not the same and since it was not originally posted that is why I asked. I also saw where you posted the hud will do the same but not at the same rate- hence my questioning to rule that out and also my last comment/question was misworded a bit- and since both are fed by datastream that is why I suggested possible interference which would apply the car itself causing the hud to read vss while not moving. HPT doesnt match the hud so something else is being added that is false. Not trying to run in circles I just like to know all the facts and be thorough to rule things to be true or not to eliminate the possibility.

Either way- something is causing it and going over everything is your first step especially the wiring from the sensor to the pcm. If you have access to a scope you can hook directly to the vss wires and watch the signal with it both hooked up to the pcm and unplugged to isolate it. If there is no output or noisy signal from the sensor itself and at the wires going right to the pcm then you know that is not the source and is likely interference or possible poor connection somewhere else and maybe nothing you can do about it.