crazy speedometer

My 95 Astro's speedometer suddenly started behaving very eradically. It climbed to 90 mph when I was only doing around 50 mph. Even at a stoplight it would be moving up and down between 0 and 20 mph. The van seems to drive ok...just don't know my actual speed. I've done some research and figure it may be the speed sensor but not sure if it is that or the PCM or something else?? Hoping someone can help. Thanks!

My 95 Astro's speedometer suddenly started behaving very eradically. It climbed to 90 mph when I was only doing around 50 mph. Even at a stoplight it would be moving up and down between 0 and 20 mph. The van seems to drive ok...just don't know my actual speed. I've done some research and figure it may be the speed sensor but not sure if it is that or the PCM or something else?? Hoping someone can help. Thanks!


Its your alternator. I just had same prob, replaced Alternator and everything is great!