Collision Avoidance Vehicle

This is what I'm trying now
I don't think Its having it though

#include <Servo.h>

Servo scanservo;     //Ping Sensor Servo

#define txPin 4
#define rxPin A4

const int motor1 = 12;
const int motor2 = 9;

const int steer1 = 13;
const int steer2 = 8;

const int PWM_M = 3;


int up = 0;
int down = 0;
int left = 0;
int right = 0;

const int a = 800;
const int turntime = 500;  //Number of milliseconds to turn when turning
const int pingPin = 6;     //Pin that the Ping sensor is attached to.
const int echoPin = 5;     //Pin that the Ping sensor is attached to.
const int scanservopin = 7;   // Pin number for scan servo
const int distancelimit = 30; 

long previousMillis = 0;       
long interval = 1000;

void setup()
{
  Serial.begin (9600);
  scanservo.attach(scanservopin); // Attach the scan servo
  pinMode(echoPin, INPUT);
  pinMode(rxPin, INPUT);
  pinMode(txPin, OUTPUT);
  
  pinMode(A0, INPUT);
  pinMode(A1, INPUT);
  pinMode(A2, INPUT);
  pinMode(A3, INPUT);

  pinMode(motor1, OUTPUT); 
  pinMode(motor2, OUTPUT); 
  pinMode(steer1, OUTPUT); 
  pinMode(steer2, OUTPUT);
  
  digitalWrite(motor1,LOW);
  digitalWrite(motor2,LOW);
  digitalWrite(steer1,LOW);
  digitalWrite(steer2,LOW);
  
}

void loop(){
  

left = analogRead(A0);
Serial.print("left:  ");
Serial.println(left);
right = analogRead(A1);
Serial.print("right:  ");
Serial.println(right);
down = analogRead(A3);
Serial.print("down:  ");
Serial.println(down);
up = analogRead(A2);
Serial.print("up:  ");
Serial.println(up);

int sensor = pingforward();
Serial.print("sensor:  ");
Serial.println(sensor);

  int leftscanval = scanleft();
  Serial.print("leftscanval:  ");
  Serial.println(leftscanval);
  int rightscanval = scanright();
  Serial.print("rightscanval:  ");
  Serial.println(rightscanval);
  int centerscanval = scancenter();
  Serial.print("centrescanval:  ");
  Serial.println(centerscanval);

  if (down < 400 && centerscanval > distancelimit){
  backward(1);
  }
  if (up < 400  && sensor > 150){
  forward(1);
    }
  if (left > 400  && leftscanval > distancelimit){
  turnleft(1);
  }
  if (right > 400  && rightscanval > distancelimit){
  turnright(1);
  }
  if (down > 400 && up > 400 && left < 400 && right < 400){
  stopmotors(1);
  }  
 
}
void turnleft(int t){
  digitalWrite (13, HIGH);                              
  digitalWrite (8, LOW);
  digitalWrite (11, HIGH);
  delayMicroseconds(t);
} 
void turnright(int t){
  digitalWrite (13, LOW);                              
  digitalWrite (8, LOW);
  digitalWrite (11, HIGH);
  delayMicroseconds(t);
}
void stopmotors(int t){
  digitalWrite (9, LOW);                              
  digitalWrite (8, LOW); 
  digitalWrite (3, LOW);
  digitalWrite (11, LOW);
  delayMicroseconds(t);
}
  void forward(int t){
  digitalWrite(12, HIGH);
  digitalWrite(9, LOW);
  digitalWrite(PWM_M, HIGH);
  delay(t);
}
void backward(int t){
  digitalWrite (9, LOW);                              
  digitalWrite (12, LOW);
  digitalWrite(PWM_M, HIGH); 
  delay(t);
}
int ping(){
  long distance, duration;
  //Send Pulse
  pinMode(pingPin, OUTPUT);
  digitalWrite(pingPin, LOW);
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pingPin, LOW);
  //Read Echo
  pinMode(echoPin, INPUT);
  duration = pulseIn(echoPin, HIGH);
  distance =(duration/2)*0.0341;
  return distance;
}
int pingforward(){
    long senseforward;
    for (int i = 0; i < 8; i++) {
    digitalWrite(txPin, LOW); // this sends out a short pulse for 10ms
    delayMicroseconds(9);
    digitalWrite(txPin, HIGH);
    delayMicroseconds(9);
    }    
    digitalWrite(txPin, LOW);
    delay(2);
    
    senseforward = analogRead(A4); // us the ping() function to see if anything is ahead.
    return senseforward;
}
int scanleft(){
  long leftscanval;
  scanservo.write(30);
  unsigned long currentMillis = millis();
 
  if(currentMillis - previousMillis > interval) {
  previousMillis = currentMillis;
  leftscanval = ping();
  } 
  return leftscanval;
}
int scanright(){
  long rightscanval;
  scanservo.write(150);
  unsigned long currentMillis = millis();
 
  if(currentMillis - previousMillis > interval) {
  previousMillis = currentMillis;
  rightscanval = ping();
  } 
  return rightscanval;
}
int scancenter(){
  long centerscanval;  
  scanservo.write(90);
  unsigned long currentMillis = millis();
 
  if(currentMillis - previousMillis > interval) {
  previousMillis = currentMillis;
  centerscanval = ping();
  } 
  
  return centerscanval;

  
 }