Speedo/VSS input to ECM


Active Member
Jul 10, 2008
What does the ECM do with the VSS/Speedo? Is it only for lockup activation? Any error codes if it is not present?

Situation is non-lock trans, the drive/driven gears are a bit off as comparing speedometer to gps shows a difference. I could fuss with the driven gear to make it a little better, but at the moment I'm also replacing the mechanical speedometer with an electronic one that can be calibrated to display correct mph. If I don't need the VSS line to the ECM, I'll just leave what gears I have and do the correction at the speedo.
besides lockup the chip uses speed input to control when timing and fueling change from 1st-2nd to 3rd to 4th gear and without that change point you could be running higher 1st and 2nd gear timing through all gears
i dont see alky in your sig but eric incorporates a timing inhibitor on alky chips below 35mph to avoid knock so until speed goes over 35 timing will be retarded and the chip may have a first gear knock ignore and thats usually speed based so if vss isnt present in higher gears if you get knock you wont have the protection of timing retard

if plans are to not run a vss or to run one thats not accurate you should contact eric about getting a new chip that will work without VSS
Hmm, the trans came without the standard trans plug, only a electric transbrake connector in its place, so ecm isn't getting 3rd and 4th signals either. Thanks, will talk to Eric.