Error Code P0412 is defined as Secondary Air Injection System Switching Valve A Circuit Malfunction.

This code shows up when the air pump or air switching valve malfunctioned with an open or short circuit.

This code is a generic trouble code, meaning it applies to all vehicles equipped with an OBD-II system. Specifications on the definition, troubleshooting and repairs, of course, vary from one make/model to another.


The AIR or Secondary Air Injection System Switching Valve is a valve controlled by the vehicle’s computer, which also controls the air injection into the engine’s exhaust system (this valve may be integral to the AIR pump). The error code refers to a problem with the circuit of the Solenoid, and not on the operation of the valve itself.

The AIR injection system works by reducing the HC (hydrocarbon), CO (carbon monoxide) and NOx (nitrogen oxide) emission by injecting fresh air to the exhaust of a catalytic converter of a warm engine or cold engine. This is what helps the engine convert hydrocarbons into water vapor (H2O) and carbon dioxide (CO2) from carbon monoxide.

The most common type of pump is the electric air pump, though there are also belt driven air pumps with an electric clutch.  The former is controlled by the PCM (powertrain control module, also known as ECM or engine control module), which is the computer of the vehicle. The PCM grounds the AIR pump relay control circuit and provide voltage to the AIR pump and solenoid valve (which may control a vacuum operated shut off valve or directly control air flow).

The fresh air supply tube comes with a check-valve, which works by preventing exhaust gas from going back up in to the AIR pump. The PCM monitors the driver that activates the AIR pumps for faults. When the PCM commands the AIR pump relay on, the control circuit voltage would be pulled close to zero. When the relay is commanded by the PCM to be off, the control circuit would have battery voltage present. If the PCM sees an unexpected voltage, it will set the Error Code P0412.

Other related secondary air injection codes are P0410, P0411, P0413, P0414, P0415, P0416, P0417, P0418, P0419, P041F, P044F, P0491, and P0492.

Common Symptoms

As with other error code, this code activates the Check Engine light, which is also its most obvious symptom. Other common symptoms include:

  • Air injection system pump is unable to come on
  • Engine running rich
  • Increase in tailpipe emissions

In some cases, the engine may not exhibit drivability issues

Possible Causes

There are many factors that can cause this error code, some of the most common causes are:

  • Too high air injection switching valve voltage, indicating open circuit
  • Too low air injection switching valve voltage, indicating short circuit
  • Open control circuit caused by damage
  • Open or short on battery feed circuit to solenoid
  • Open or short on battery feed to relay control circuit
  • PCM sets the code from diagnostic input from air injection system driver

How to Check

As with in other error codes, technicians start their diagnosis of this code by scanning the codes and documenting the freeze frame data to verify the problem

Then, they clear the engine codes and retest the air injection system for proper operation

Next, they test the air injection switching valve which controls the air injection pump operation during tests

Then, they check the resistance of the air injection pump and air injection switching valve

Next, they check the air injection pump for proper voltage between power pins and ground.

How to Fix

Repairs for this error code are simple and straightforward, which include:

  • Replacement of air injection switch valve
  • Replacement of air injection pump and power relay
  • Repair or replacement of the wiring to air injection pump power relay connection

The job of the air injection pump system is to reduce the emission coming out of the exhaust, which will prevent the vehicle from failing emission testing. Problems with it should not cause drivability issues.

A short in the air injection pump circuit can cause short to the air injection driver in the PCM, which is why it should be considered when diagnosing the problem.