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P0412 Code: Causes, Symptoms, and Ways to Repair It! 

  • Cars Explained
  • Gerard Stevens
  • 5 minutes

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The Check Engine Light turning on while you drive can cause quite confusion. We know that the Check Engine Light illuminates various diagnostic trouble codes (DTCs). But, is there increased emission from the taillight? When you diagnose the issue, it identifies that your car activated a P0412 code. What does that engine error code imply? 

The code denotes your car has a ‘Secondary Air Injection System Switching Valve A Circuit Malfunction. Numerous things can cause this, so a technician must identify the precise cause in your case to clear the code. The code usually appears on car brands like BMW, Cadillac, Chevrolet, Ford, Lexus, and Toyota, to name a few.  

So, what all can cause the P0412 code to activate? What all symptoms show up in your car when this DTC activates? How can you fix it? Continue reading to know in detail about this error code! 

What is a P0412 code? 

The computer in the car, which also controls the air injection into the exhaust system, is in charge of the Secondary Air Injection System Switching Valve. Unfortunately, the OBD P0412 error code refers to an issue with the solenoid’s circuit rather than the valve’s functionality. 

A check valve is built into the fresh air supply tube, preventing exhaust gas from returning to the air injection pump. The powertrain control module (PCM) checks for errors in the driver that turns on the air injection pumps. The control circuit voltage will nearly become zero when the PCM instructs the air injection pump relay to turn on.  

The control circuit would have battery voltage when the PCM instructs the relay to be off. A sudden voltage will cause the PCM to set the P0412 code in the system. 

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How serious is the P0412 code? 

These can be the consequences if the code activates. 

  • The air injection pump system tends to reduce exhaust emissions. Still, it also has the potential to make the car fail in emission tests. 
  • The car fails emission testing when the Check Engine Light illuminates. 
  • The air injection pump shouldn’t lead to drive symptoms other than the Check Engine Light illuminating.  

What is the P0418 code? Here’s more info! 

What causes a P0412 code? 

These are some of the reasons why the code activates in your car. 

  • The excessive voltage at the air injection switching valve suggests an open circuit 
  • Too low voltage at the air injection switching valve, signifying a short circuit 
  • The control circuit is open 
  • The battery feed circuit to the solenoid is open or shorted 
  • Battery feed to the relay control circuit gets open/short 
  • PCM will be faulty 
  • Carbon gets accumulated in the hoses, ducts, and other parts 

What are the symptoms of the P0412 code? 


These are common symptoms you can observe while the code activates in your car.  

  • The Check Engine Light turns on. It is the most common symptom of the P0412 code. 
  • The tailpipe emission increased greatly.  
  • Engine running rich.  
  • There’s a chance the air injection system pump won’t turn on. 
  • The engine has poor acceleration.  
  • A check engine light may be the only drive symptom the engine exhibits. 

How does the mechanic diagnose the P0412 code? 

A mechanic will perform the following steps while diagnosing the code. 

  • Verify the issue by scanning the OBD codes and paperwork, then freezing the data. 
  • Reset the engine’s codes and check the air injection system’s working again. Diagnose first if the code reappears. 
  • To regulate the operation of the air injection pump, test the air injection switching valve. 
  • Then they will examine the resistance of the air injection pump and the air injection switching valve. 
  • Then check if there is a proper voltage between the power and ground pins on the air injection pump. 
  • Check for PCM issues and make any necessary repairs or replacements. 

Common mistakes that happen while diagnosing the code 

  • Not verifying that the air injection pump’s battery voltage is above eight volts before replacing the pump since no air pumps out from it.  
  • Not repairing a defective air injection pump or air switching valve before examining the air injection pump power relay for burnt wire connections.

What repairs can fix the P0412 code? 

How do I fix code P0412? These are some fixes you can do to clear the issue. 

  • Replacement of the air injection pump and power relay. 
  • Changing the air injection switch valve. 
  • Fixing the wiring to the air injection pump power relay. 
  • Replacement of the air injection solenoid. 

The bottom line 

  • P0412 code means ‘Secondary Air Injection System Switching Valve A Circuit Malfunction.’ 
  • The Check Engine Light illuminates when the code activates in your car. 
  • The engine will run rich, and the acceleration becomes poor.  
  • You can repair the code by replacing the air injection pump and power relay, air injection switch valve, and air injection solenoid.  

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