In grid.celledit.js:

Add the method:

prevCell : function (iRow,iCol) {

return this.each(function (){

var $t = this, nCol=false, tmp;

if (!$t.grid || $t.p.cellEdit !== true) {return;}

// try to find next editable cell

for (var i=iCol-1; i>=0; i–) {

if ( $t.p.colModel.editable ===true) {

nCol = i; break;

}

}

if(nCol !== false) {

$($t).saveCell(iRow,iCol);

$($t).editCell(iRow,nCol,true);

} else {

if ($t.p.savedRow.length >0) {

$($t).saveCell(iRow,iCol);

}

}

});

},