Cant read anything from Winsen ZH03b sensor

//******************************
 //*Abstract: Read value of PM1,PM2.5 and PM10 of air quality
 //*Product Link: http://www.dfrobot.com.cn/goods-1113.html
 //*
 //8
 //*The RX pin on the sensor connects to pin 10 on the Arduino
 //*The TX pin on the sensor connects to pin 11 on the Arduino
 //
 //*Version：V3.1
 //*Author：Zuyang @ HUST
 //*Date：March.25.2016
 //******************************
#include <Arduino.h>
#include <SoftwareSerial.h>
#define LENG 31   //0x42 + 31 bytes equal to 32 bytes
unsigned char buf[LENG];
 
int PM01Value=0;          //define PM1.0 value of the air detector module
int PM2_5Value=0;         //define PM2.5 value of the air detector module
int PM10Value=0;         //define PM10 value of the air detector module
 
SoftwareSerial PMSerial(10, 11); // RX, TX
 
void setup()
{
  PMSerial.begin(9600);
  PMSerial.setTimeout(1500);
  Serial.begin(9600);
}
 
void loop()
{
  if(PMSerial.find(0x42)){
    PMSerial.readBytes(buf,LENG);
 
    if(buf[0] == 0x4d){
      if(checkValue(buf,LENG)){
        PM01Value=transmitPM01(buf); //count PM1.0 value of the air detector module
        PM2_5Value=transmitPM2_5(buf);//count PM2.5 value of the air detector module
        PM10Value=transmitPM10(buf); //count PM10 value of the air detector module
      }
    }
  }
 
  static unsigned long OledTimer=millis();
    if (millis() - OledTimer >=1000)
    {
      OledTimer=millis();
 
      Serial.print("PM1.0: ");
      Serial.print(PM01Value);
      Serial.println("  ug/m3");
 
      Serial.print("PM2.5: ");
      Serial.print(PM2_5Value);
      Serial.println("  ug/m3");
 
      Serial.print("PM1 0: ");
      Serial.print(PM10Value);
      Serial.println("  ug/m3");
      Serial.println();
    }
 
}
char checkValue(unsigned char *thebuf, char leng)
{
  char receiveflag=0;
  int receiveSum=0;
 
  for(int i=0; i<(leng-2); i++){
  receiveSum=receiveSum+thebuf[i];
  }
  receiveSum=receiveSum + 0x42;
 
  if(receiveSum == ((thebuf[leng-2]<<8)+thebuf[leng-1]))  //check the serial data
  {
    receiveSum = 0;
    receiveflag = 1;
  }
  return receiveflag;
}
 
int transmitPM01(unsigned char *thebuf)
{
  int PM01Val;
  PM01Val=((thebuf[3]<<8) + thebuf[4]); //count PM1.0 value of the air detector module
  return PM01Val;
}
 
//transmit PM Value to PC
int transmitPM2_5(unsigned char *thebuf)
{
  int PM2_5Val;
  PM2_5Val=((thebuf[5]<<8) + thebuf[6]);//count PM2.5 value of the air detector module
  return PM2_5Val;
  }
 
//transmit PM Value to PC
int transmitPM10(unsigned char *thebuf)
{
  int PM10Val;
  PM10Val=((thebuf[7]<<8) + thebuf[8]); //count PM10 value of the air detector module
  return PM10Val;
}