how to uncheck the checkbox using function in angular 2 typescript?

To control checkbox in typescript you have to use something like this

var element = <HTMLInputElement> document.getElementById("IDOfCheckbox");
element.checked = true;

First, you need object array which contains one string property to display and one boolean property i.e selected to check and uncheck the checkbox.

resetFilters(){
 this.vehicleClassArr.every(function(item:any) {
        return item.selected == false;
      })
}

<ul>
  <li> <input type="checkbox" [(ngModel)]="selectedAll" (change)="selectAll();"/>
  </li>
  <li *ngFor="let veh of vehicleClassArr"> 
  <input type="checkbox" [(ngModel)]="veh.selected">
  {{veh.name}}
  </li>
</ul>
<button class="filter-reset-btn" (click)="resetFilters()">Reset to Default</button>

Add an additional field "checked" to your vehicleClass-object and bind to this via ngModel

<div class="filter2">
          <label class="containe" 
          *ngFor="let veh of vehicleClassArr; let ndx=index;">
          {{veh}}
          <input id="myCheck{{ndx}}" type="checkbox" name="{{veh}}" value="{{veh}}" 
           [(ngModel)]="veh.checked" (change)="filterSearchResults($event, veh,'vehicleClass')">
              <span class="checkmark"></span>
          </label>
</div>

Then adjust your method resetFilters() as follows

private resetFilters(): void {
   this.vehicleClassArr.forEach(element => {
      element.checked = false;
   });
}