Rxjs subject switchmap http error

Question

I use Subject, switchMapand .next()to cancel previous pending http calls when starting a new request http.get().

The problem is that I am processing an HTTP error (for example, timeout), the method _postMPCHC.next(...)called in html no longer works ... Do I need to recreate the error subscription? How?

import {Component} from '@angular/core';
import {NavController, NavParams, Toast} from 'ionic-angular';
import {Http, URLSearchParams} from '@angular/http';
import {AppSettings} from '../../appSettings';
import {Subject} from 'rxjs/Subject';


@Component({
  templateUrl: 'build/pages/video/video.html'
})
export class VideoPage {
  _postMPCHC: any= new Subject();

  constructor(private http: Http, private nav: NavController) {
    this.defineHttp();
  }

  defineHttp() {

    var sub = this._postMPCHC.switchMap((x: string) => {
      let params: URLSearchParams = new URLSearchParams();
      params.set('token', AppSettings.API_TOKEN);
      params.set('prog', 'mhz');
      params.set('prog', 'mpchc');
      params.set('action', x);

      return this.http.get(AppSettings.API_ENDPOINT, { search: params })

    }).timeout(5000, new Error('timeout exceeded')).subscribe(x => { },
      error => {
        let toast = Toast.create({
          message: 'Server response: ' + <any>error,
          duration: 3000,
          position: 'middle'
        });
        this.nav.present(toast);
      })

  }
}