Go get the latest 'Release' version of Marlin from GitHub:
https://github.com/MarlinFirmware/Marlin (Do not grab the development version which is more 'current' than the last Release version!)
Go find this code in Marlin_main.cpp. This code controls the probing across both the X and Y axis. Change it to be what ever you desire it does:
Code:
for (int yProbe = front_probe_bed_position; yProbe <= back_probe_bed_position; yProbe += yGridSpacing) {
int xProbe, xInc;
if (zig)
xProbe = left_probe_bed_position, xInc = xGridSpacing;
else
xProbe = right_probe_bed_position, xInc = -xGridSpacing;
// If topo_flag is set then don't zig-zag. Just scan in one direction.
// This gets the probe points in more readable order.
if (!topo_flag) zig = !zig;
for (int xCount = 0; xCount < auto_bed_leveling_grid_points; xCount++) {
// raise extruder
float measured_z,
z_before = probePointCounter == 0 ? Z_RAISE_BEFORE_PROBING : current_position[Z_AXIS] + Z_RAISE_BETWEEN_PROBINGS;