I have an 87 Formula 350 and have been going crazy trying to fix my speedo. I have a few questions. If my VSS is bad, will it turn on my SES light? According to the original owner, it has been out for some time, so will the ses light be on or will it be stored as a code? If so, how do I check for codes? Any help woupld be greatly aprreciated.

 

It probably will not set a code.

 

The absence of a VSS signal will set a code 24, particularly when coasting and downshifting/decelerating. A bad VSS (garbled signal or otherwise) will probably not set a code.

Check the tech articles for how to pull and decipher trouble codes.