2001 Olds Silhouette- Left rear speed sensor signal erratic

[daleluce]

Hey everyone. Thanks in advance for any help.

I have a 2001 silhouette with an abs light. I went to a garage and plugged it in and got this message..

"c1227 Left rear speed sensor signal erratic"

I'm wondering if someone can point me in the right direction of troubleshooting this, I think cleaning some connections and checking for damage is probably the first step, but I'm not sure where to start. Thanks!