user55701: int scvVal = 6;
int drvVal = 9;
int sensorVal = A1;
void setup() { 
    Serial.begin(9600);
    pinMode(6, OUTPUT);
    pinMode(9, OUTPUT);   
 }
void loop(){
 sensorVal = analogRead(A1);


 Serial.print("Sensor Value: ");
 Serial.print(sensorVal);

 float voltage = (sensorVal*5.0)/1024.0; 
    Serial.print("Volts: ");
    Serial.print(voltage);

 float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0;
 float pressure_bar = pressure_pascal/10e5;
   Serial.print("Pressure = ");
   Serial.print(pressure_bar); 
   Serial.println(" bars");
   Serial.print("Pressure = ");
   {
 for(int a = 255; a>=0;a--)
 {
   analogWrite(6,a); 
 if (pressure_bar = 1600){
   analogWrite (6, a);
 if (pressure_bar > 1600){
   analogWrite (6, a);
 }
 for(int a = 0; a<256; a++)
 {
  analogWrite(6, a);
 {
 if(pressure_bar < 1600){
  analogWrite (6, a); 
 }
 for(int b = 255; b>=0;b--)
 {
 analogWrite(9, b);
 {
 if (pressure_bar == 1600){
   analogWrite (9, b);
 if(pressure_bar < 1600){
   analogWrite (9, b);
}
 for(int b = 0; b<256; b++)
 {
   analogWrite(9, b);
 { 
if (pressure_bar > 1600){
   analogWrite (9, b);  
   }
  }


user42539: Look at your open brackets { vs closing brackets, }. You need the same number of each. If have this in the Arduino IDE and use CTRL-T, they are somewhat easy to find.  I just looked, and I can spot them pretty easily.
int scvVal = 6; 
int drvVal = 9; 
int sensorVal = A1; 
void setup() 
{ 
Serial.begin(9600); 
pinMode(6, OUTPUT); 
pinMode(9, OUTPUT);
} 
void loop()
{ 
sensorVal = analogRead(A1);
Serial.print("Sensor Value: "); 
Serial.print(sensorVal);
float voltage = (sensorVal*5.0)/1024.0; 
Serial.print("Volts: "); 
Serial.print(voltage);
float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0; 
float pressure_bar = pressure_pascal/10e5; 
Serial.print("Pressure = "); 
Serial.print(pressure_bar); 
Serial.println(" bars"); 
Serial.print("Pressure = "); 
{                            << bracket for what?
for(int a = 255; a>=0;a--) { << missing closing bracket
  analogWrite(6,a); 
  if (pressure_bar = 1600){   << missing closing bracket
   analogWrite (6, a); 
     if (pressure_bar > 1600){ 
     analogWrite (6, a); 
     } 
  for(int a = 0; a<256; a++) { 
    analogWrite(6, a); 
    {                      << wrong direction
    if(pressure_bar < 1600){ 
       analogWrite (6, a); 
    } 
  for(int b = 255; b>=0;b--) { 
    analogWrite(9, b); 
   {                           << wrong direction
    if (pressure_bar == 1600){ << missing closing bracket
      analogWrite (9, b); 
      if(pressure_bar < 1600){ << missing closing bracket
        analogWrite (9, b); 
    } 
   for(int b = 0; b<256; b++) { 
     analogWrite(9, b); 
   {                            << wrong direction
   if (pressure_bar > 1600){ 
     analogWrite (9, b);
   } 
}  << closing bracket for loop


user31105: Some guidelines for programming:
Start each statement on a new line
int scvVal = 6; 
int drvVal = 9; 
int sensorVal = A1; 
void setup() { 
Serial.begin(9600); 
pinMode(6, OUTPUT); 
pinMode(9, OUTPUT);
} void loop(){ 
sensorVal = analogRead(A1);

Serial.print("Sensor Value: "); Serial.print(sensorVal);

float voltage = (sensorVal*5.0)/1024.0; Serial.print("Volts: "); Serial.print(voltage);

float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0; 
float pressure_bar = pressure_pascal/10e5; 
Serial.print("Pressure = "); 
Serial.print(pressure_bar); 
Serial.println(" bars"); 
Serial.print("Pressure = "); { 
for(int a = 255; a>=0;a--) { 
analogWrite(6,a); 
if (pressure_bar = 1600){ 
analogWrite (6, a); 
if (pressure_bar > 1600){ 
analogWrite (6, a); } 
for(int a = 0; a<256; a++) { 
analogWrite(6, a); { 
if(pressure_bar < 1600){ 
analogWrite (6, a); } 
for(int b = 255; b>=0;b--) { 
analogWrite(9, b); { 
if (pressure_bar == 1600){ 
analogWrite (9, b); 
if(pressure_bar < 1600){ 
analogWrite (9, b); } 
for(int b = 0; b<256; b++) { 
analogWrite(9, b); { 
if (pressure_bar > 1600){ 
analogWrite (9, b);
} }

Use brackets and align them
.. so each pair of { and } is on the same column and align code with brackets to be indented 2, 3 or 4 spaces
int scvVal = 6; 
int drvVal = 9; 
int sensorVal = A1; 
void setup() 
{ 
  Serial.begin(9600); 
  pinMode(6, OUTPUT); 
  pinMode(9, OUTPUT);
} 
void loop()
{ 
  sensorVal = analogRead(A1);

  Serial.print("Sensor Value: "); 
  Serial.print(sensorVal);

  float voltage = (sensorVal*5.0)/1024.0; Serial.print("Volts: "); 
  Serial.print(voltage);

  float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0; 
  float pressure_bar = pressure_pascal/10e5; 
  Serial.print("Pressure = "); 
  Serial.print(pressure_bar); 
  Serial.println(" bars"); 
  Serial.print("Pressure = "); 
  { 
    for(int a = 255; a>=0;a--) 
    { 
      analogWrite(6,a); 
      if (pressure_bar = 1600)
      { 
        analogWrite (6, a); 
        if (pressure_bar > 1600)
        { 
          analogWrite (6, a);  
        }   
        for(int a = 0; a<256; a++) 
        { 
          analogWrite(6, a); 
          {   
            if(pressure_bar < 1600)
            {   
              analogWrite (6, a); 
            } 
            for(int b = 255; b>=0;b--) 
            { 
              analogWrite(9, b); 
              {  
                if (pressure_bar == 1600)
                { 
                  analogWrite (9, b); 
                  if(pressure_bar < 1600)
                  {  
                    analogWrite (9, b); 
                  } 
                  for(int b = 0; b<256; b++) 
                  { 
                    analogWrite(9, b); 
                    { 
                      if (pressure_bar > 1600)
                      {    
                        analogWrite (9, b);
                      }
                    }

Remove superfluous brackets
As you can see, you are having some superfluous/missing brackets. What you want is probably something like:
int scvVal = 6; 
int drvVal = 9; 
int sensorVal = A1; 
void setup() 
{ 
  Serial.begin(9600); 
  pinMode(6, OUTPUT); 
  pinMode(9, OUTPUT);
} 
void loop()
{ 
  sensorVal = analogRead(A1);

  Serial.print("Sensor Value: "); 
  Serial.print(sensorVal);

  float voltage = (sensorVal*5.0)/1024.0; Serial.print("Volts: "); 
  Serial.print(voltage);

  float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0; 
  float pressure_bar = pressure_pascal/10e5; 
  Serial.print("Pressure = "); 
  Serial.print(pressure_bar); 
  Serial.println(" bars"); 
  Serial.print("Pressure = "); 

  for(int a = 255; a>=0;a--) 
  { 
    analogWrite(6,a); 
    if (pressure_bar = 1600)
    { 
      analogWrite (6, a);
    }
    if (pressure_bar > 1600)
    { 
      analogWrite (6, a);  
    } 
  }
  for(int a = 0; a<256; a++) 
  {
    analogWrite(6, a); 
    if(pressure_bar < 1600)
    {   
      analogWrite (6, a); 
    }
  } 
  for(int b = 255; b>=0;b--) 
  { 
    analogWrite(9, b); 
    if (pressure_bar == 1600)
    { 
      analogWrite (9, b); 
    }
    if(pressure_bar < 1600)
    {  
      analogWrite (9, b); 
    } 
  }
  for(int b = 0; b<256; b++) 
  { 
    analogWrite(9, b); 
    if (pressure_bar > 1600)
    {    
      analogWrite (9, b);
    }
  }
}

Remove duplicate code
In the if statement, you perform twice the same code (both you send an analogWrite with the same value, so the code (from the for loops can be reduced to:
  for(int a = 255; a>=0;a--) 
  { 
    analogWrite(6,a); 
    if (pressure_bar >= 1600)
    { 
      analogWrite (6, a);
    }
  }
  for(int a = 0; a<256; a++) 
  {
    analogWrite(6, a); 
    if(pressure_bar <= 1600)
    {   
      analogWrite (6, a); 
    }
  } 
  for(int b = 255; b>=0;b--) 
  { 
    analogWrite(9, b); 
    if (pressure_bar <= 1600)
    { 
      analogWrite (9, b); 
    } 
  }
  for(int b = 0; b<256; b++) 
  { 
    analogWrite(9, b); 
    if (pressure_bar >= 1600)
    {    
      analogWrite (9, b);
    }
  }
}

Unclear
What is unclear why you first write an analog value, and directly afterward (in each if) you write the same value. I'm not sure what you really want here. Either you want to write to a different pin, or you want a delay (to have the value having some effect), I'm just not sure.

55701: <pre><code>int scvVal = 6;
int drvVal = 9;
int sensorVal = A1;
void setup() { 
    Serial.begin(9600);
    pinMode(6, OUTPUT);
    pinMode(9, OUTPUT);   
 }
void loop(){
 sensorVal = analogRead(A1);


 Serial.print("Sensor Value: ");
 Serial.print(sensorVal);

 float voltage = (sensorVal*5.0)/1024.0; 
    Serial.print("Volts: ");
    Serial.print(voltage);

 float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0;
 float pressure_bar = pressure_pascal/10e5;
   Serial.print("Pressure = ");
   Serial.print(pressure_bar); 
   Serial.println(" bars");
   Serial.print("Pressure = ");
   {
 for(int a = 255; a&gt;=0;a--)
 {
   analogWrite(6,a); 
 if (pressure_bar = 1600){
   analogWrite (6, a);
 if (pressure_bar &gt; 1600){
   analogWrite (6, a);
 }
 for(int a = 0; a&lt;256; a++)
 {
  analogWrite(6, a);
 {
 if(pressure_bar &lt; 1600){
  analogWrite (6, a); 
 }
 for(int b = 255; b&gt;=0;b--)
 {
 analogWrite(9, b);
 {
 if (pressure_bar == 1600){
   analogWrite (9, b);
 if(pressure_bar &lt; 1600){
   analogWrite (9, b);
}
 for(int b = 0; b&lt;256; b++)
 {
   analogWrite(9, b);
 { 
if (pressure_bar &gt; 1600){
   analogWrite (9, b);  
   }
  }
</code></pre>
 42539: <p>Look at your open brackets { vs closing brackets, }. You need the same number of each. If have this in the Arduino IDE and use CTRL-T, they are somewhat easy to find.  I just looked, and I can spot them pretty easily.</p>

<pre><code>int scvVal = 6; 
int drvVal = 9; 
int sensorVal = A1; 
void setup() 
{ 
Serial.begin(9600); 
pinMode(6, OUTPUT); 
pinMode(9, OUTPUT);
} 
void loop()
{ 
sensorVal = analogRead(A1);
Serial.print("Sensor Value: "); 
Serial.print(sensorVal);
float voltage = (sensorVal*5.0)/1024.0; 
Serial.print("Volts: "); 
Serial.print(voltage);
float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0; 
float pressure_bar = pressure_pascal/10e5; 
Serial.print("Pressure = "); 
Serial.print(pressure_bar); 
Serial.println(" bars"); 
Serial.print("Pressure = "); 
{                            &lt;&lt; bracket for what?
for(int a = 255; a&gt;=0;a--) { &lt;&lt; missing closing bracket
  analogWrite(6,a); 
  if (pressure_bar = 1600){   &lt;&lt; missing closing bracket
   analogWrite (6, a); 
     if (pressure_bar &gt; 1600){ 
     analogWrite (6, a); 
     } 
  for(int a = 0; a&lt;256; a++) { 
    analogWrite(6, a); 
    {                      &lt;&lt; wrong direction
    if(pressure_bar &lt; 1600){ 
       analogWrite (6, a); 
    } 
  for(int b = 255; b&gt;=0;b--) { 
    analogWrite(9, b); 
   {                           &lt;&lt; wrong direction
    if (pressure_bar == 1600){ &lt;&lt; missing closing bracket
      analogWrite (9, b); 
      if(pressure_bar &lt; 1600){ &lt;&lt; missing closing bracket
        analogWrite (9, b); 
    } 
   for(int b = 0; b&lt;256; b++) { 
     analogWrite(9, b); 
   {                            &lt;&lt; wrong direction
   if (pressure_bar &gt; 1600){ 
     analogWrite (9, b);
   } 
}  &lt;&lt; closing bracket for loop
</code></pre>
 31105: <p>Some guidelines for programming:</p>

<p><strong>Start each statement on a new line</strong></p>

<pre><code>int scvVal = 6; 
int drvVal = 9; 
int sensorVal = A1; 
void setup() { 
Serial.begin(9600); 
pinMode(6, OUTPUT); 
pinMode(9, OUTPUT);
} void loop(){ 
sensorVal = analogRead(A1);

Serial.print("Sensor Value: "); Serial.print(sensorVal);

float voltage = (sensorVal*5.0)/1024.0; Serial.print("Volts: "); Serial.print(voltage);

float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0; 
float pressure_bar = pressure_pascal/10e5; 
Serial.print("Pressure = "); 
Serial.print(pressure_bar); 
Serial.println(" bars"); 
Serial.print("Pressure = "); { 
for(int a = 255; a&gt;=0;a--) { 
analogWrite(6,a); 
if (pressure_bar = 1600){ 
analogWrite (6, a); 
if (pressure_bar &gt; 1600){ 
analogWrite (6, a); } 
for(int a = 0; a&lt;256; a++) { 
analogWrite(6, a); { 
if(pressure_bar &lt; 1600){ 
analogWrite (6, a); } 
for(int b = 255; b&gt;=0;b--) { 
analogWrite(9, b); { 
if (pressure_bar == 1600){ 
analogWrite (9, b); 
if(pressure_bar &lt; 1600){ 
analogWrite (9, b); } 
for(int b = 0; b&lt;256; b++) { 
analogWrite(9, b); { 
if (pressure_bar &gt; 1600){ 
analogWrite (9, b);
} }
</code></pre>

<p><strong>Use brackets and align them</strong></p>

<p>.. so each pair of { and } is on the same column and align code with brackets to be indented 2, 3 or 4 spaces</p>

<pre><code>int scvVal = 6; 
int drvVal = 9; 
int sensorVal = A1; 
void setup() 
{ 
  Serial.begin(9600); 
  pinMode(6, OUTPUT); 
  pinMode(9, OUTPUT);
} 
void loop()
{ 
  sensorVal = analogRead(A1);

  Serial.print("Sensor Value: "); 
  Serial.print(sensorVal);

  float voltage = (sensorVal*5.0)/1024.0; Serial.print("Volts: "); 
  Serial.print(voltage);

  float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0; 
  float pressure_bar = pressure_pascal/10e5; 
  Serial.print("Pressure = "); 
  Serial.print(pressure_bar); 
  Serial.println(" bars"); 
  Serial.print("Pressure = "); 
  { 
    for(int a = 255; a&gt;=0;a--) 
    { 
      analogWrite(6,a); 
      if (pressure_bar = 1600)
      { 
        analogWrite (6, a); 
        if (pressure_bar &gt; 1600)
        { 
          analogWrite (6, a);  
        }   
        for(int a = 0; a&lt;256; a++) 
        { 
          analogWrite(6, a); 
          {   
            if(pressure_bar &lt; 1600)
            {   
              analogWrite (6, a); 
            } 
            for(int b = 255; b&gt;=0;b--) 
            { 
              analogWrite(9, b); 
              {  
                if (pressure_bar == 1600)
                { 
                  analogWrite (9, b); 
                  if(pressure_bar &lt; 1600)
                  {  
                    analogWrite (9, b); 
                  } 
                  for(int b = 0; b&lt;256; b++) 
                  { 
                    analogWrite(9, b); 
                    { 
                      if (pressure_bar &gt; 1600)
                      {    
                        analogWrite (9, b);
                      }
                    }
</code></pre>

<p><strong>Remove superfluous brackets</strong></p>

<p>As you can see, you are having some superfluous/missing brackets. What you want is probably something like:</p>

<pre><code>int scvVal = 6; 
int drvVal = 9; 
int sensorVal = A1; 
void setup() 
{ 
  Serial.begin(9600); 
  pinMode(6, OUTPUT); 
  pinMode(9, OUTPUT);
} 
void loop()
{ 
  sensorVal = analogRead(A1);

  Serial.print("Sensor Value: "); 
  Serial.print(sensorVal);

  float voltage = (sensorVal*5.0)/1024.0; Serial.print("Volts: "); 
  Serial.print(voltage);

  float pressure_pascal = (400.0*((float)voltage-0.5))*1000000.0; 
  float pressure_bar = pressure_pascal/10e5; 
  Serial.print("Pressure = "); 
  Serial.print(pressure_bar); 
  Serial.println(" bars"); 
  Serial.print("Pressure = "); 

  for(int a = 255; a&gt;=0;a--) 
  { 
    analogWrite(6,a); 
    if (pressure_bar = 1600)
    { 
      analogWrite (6, a);
    }
    if (pressure_bar &gt; 1600)
    { 
      analogWrite (6, a);  
    } 
  }
  for(int a = 0; a&lt;256; a++) 
  {
    analogWrite(6, a); 
    if(pressure_bar &lt; 1600)
    {   
      analogWrite (6, a); 
    }
  } 
  for(int b = 255; b&gt;=0;b--) 
  { 
    analogWrite(9, b); 
    if (pressure_bar == 1600)
    { 
      analogWrite (9, b); 
    }
    if(pressure_bar &lt; 1600)
    {  
      analogWrite (9, b); 
    } 
  }
  for(int b = 0; b&lt;256; b++) 
  { 
    analogWrite(9, b); 
    if (pressure_bar &gt; 1600)
    {    
      analogWrite (9, b);
    }
  }
}
</code></pre>

<p><strong>Remove duplicate code</strong></p>

<p>In the if statement, you perform twice the same code (both you send an <code>analogWrite</code> with the same value, so the code (from the for loops can be reduced to:</p>

<pre><code>  for(int a = 255; a&gt;=0;a--) 
  { 
    analogWrite(6,a); 
    if (pressure_bar &gt;= 1600)
    { 
      analogWrite (6, a);
    }
  }
  for(int a = 0; a&lt;256; a++) 
  {
    analogWrite(6, a); 
    if(pressure_bar &lt;= 1600)
    {   
      analogWrite (6, a); 
    }
  } 
  for(int b = 255; b&gt;=0;b--) 
  { 
    analogWrite(9, b); 
    if (pressure_bar &lt;= 1600)
    { 
      analogWrite (9, b); 
    } 
  }
  for(int b = 0; b&lt;256; b++) 
  { 
    analogWrite(9, b); 
    if (pressure_bar &gt;= 1600)
    {    
      analogWrite (9, b);
    }
  }
}
</code></pre>

<p><strong>Unclear</strong></p>

<p>What is unclear why you first write an analog value, and directly afterward (in each if) you write the same value. I'm not sure what you really want here. Either you want to write to a different pin, or you want a delay (to have the value having some effect), I'm just not sure.</p>
