Okay it seems that the PH_WHEEL does not like to be overly constrained. I am getting the same problem with 6.40.5 but it goes away when I change the code to this:

phcon_setparams2(my.wheelFL, vector(my.targetSteer-2,my.targetSteer+2,0), nullvector, vector(my.suspensionERP, my.suspensionCFM,0));
phcon_setparams2(my.wheelFR, vector(my.targetSteer-2,my.targetSteer+2,0), nullvector, vector(my.suspensionERP, my.suspensionCFM,0));