Put this under OnPlayerText callback:
if(strcmp(text,"!pcj",true) == 0)
{
new Float:x,
Float:y,
Float:z,
Float:angle,
string[64],
pveh[MAX_PLAYERS] = 0;
GetPlayerPos(playerid,x,y,z);
GetPlayerFacingAngle(playerid,angle);
pveh[playerid] = CreateVehicle(191,x,y,z,angle,-1,-1);
PutPlayerInVehicle(playerid,pveh[playerid]);
SendClientMessage(playerid,0xFFFFFFFF,"Spawned a PCJ-600!");
return 0;
}
In-game type !pcj.