ABS wheel sensor?

Your vehicle has 4 wheel speed sensors (as part of the hub and bearing assemblies) One at each wheel and a corrosponding harness for each.
First you would need to diagnose the faulty one to know which to replace. Hub & bearing assemblies with the sensor bult in (not serviced separately) makes it cost prohibitive to replace them untill you get the failed part.
The tools usually used to diagnose a faulty wheel speed sensor is a diagnostic computer and a digital multimeter. The ability to lift all four wheels off the ground at the same time is also helpful.
If you have these than you would scan the abs module watching live data from all four wheels, if one does not send or the signal drops out at slower speeds on one, that would be the suspect senspr. next you would check resistance of the sensor and continuity of the harness (to the sensor and to the abs module) to determine if the sensor is at fault or the harness to the module. Both parts have a know history of failure in GM "N" body vehicles, so one is no more suspect than the other.

abs and brake light on code reader says left side speed sensor no signal befor i change hub is there a way to check sensor 2001 olds alero with abs

You would need an oscilloscope to view the signal. GM has had a huge problem with their ABS sensors. The sensor isn't actually the problem. A little normal play develops in the bearing. The tone ring moves a little and causes the signal to drop out. The only fix is to replace the bearing assembly.

thanks nice to know jda