What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. Although generic, specific repair steps may vary by make/model.
The secondary air injection (AIR) system switching valve is the computer-controlled valve that controls air injection into the engine’s exhaust system (this valve may be integral to the AIR pump). This code deals with an issue in the SOLENOID circuit, not the operation of the AIR pump itself.
The AIR injection system reduces hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) emissions by injecting fresh air into the exhaust ports of a cold engine or the catalytic converter of a hot engine. This helps convert hydrocarbons into water vapor (H₂O) and carbon monoxide into carbon dioxide (CO₂).
Generally, the electric air pump is the most common type, though there may be belt-driven air pumps with an electric clutch. The electric air pump is controlled by the PCM (powertrain control module), which grounds the AIR pump relay control circuit and provides voltage to the AIR pump and solenoid valve (which may control a vacuum-operated shut-off valve or directly control airflow). There is a check valve in the fresh air supply tube that prevents exhaust gases from flowing back into the AIR pump.
The PCM monitors the driver that activates the AIR pump for faults. When the PCM commands the AIR pump relay on, the control circuit voltage is naturally pulled near zero. When the relay is commanded off, the control circuit should have battery voltage present. If the PCM detects a voltage that is not as expected, P0412 will be set.
Other secondary air injection system fault codes include P0410, P0411, P0413, P0414, P0415, P0416, P0417, P0418, P0419, P041F, P044F, P0491, and P0492.
Symptoms
Symptoms of a P0412 DTC may include:
• MIL (Malfunction Indicator Lamp) illuminated
• Increased exhaust emissions
• Rich running engine
Causes
Potential causes of a P0412 code include:
• Short to ground in the control circuit
• Short to voltage in the control circuit
• Open control circuit due to damage, etc.
• Open or short in the battery supply circuit to the solenoid
• Open or short in the battery supply to the relay control circuit
Possible Solutions
If you have access to a scan tool, with KOEO (Key On Engine Off), activate and deactivate the AIR pump solenoid. If the solenoid does not operate, disconnect the solenoid and use a voltmeter to check that voltage is supplied to the solenoid when commanded and also for a good ground. If there is voltage supplied and a good ground, check for a proper connection at the solenoid wiring harness connector. If the connection is good, replace the solenoid. If there is no voltage supplied to the connector when commanding the solenoid, locate the AIR pump relay and check for fused battery voltage on the switched side of the circuit that powers the AIR pump; if not, check for a blown fuse or open in the wiring. Repair and retest.
If battery voltage is present on the voltage supply side of the relay, a quick way to check proper solenoid and AIR pump operation is to use a fused jumper and manually activate it. To do this, connect battery voltage to the switched voltage supply of the AIR pump. This is typically terminals 30 and 87 in the relay diagram (not always). If the solenoid (and possibly the AIR pump) operates, then you know your wiring and solenoid are correct. If it does not activate, open the wiring harness and find the open or short in the AIR pump solenoid supply and fix it. If connecting the solenoid to battery voltage activates the solenoid, it’s time to check for voltage present with KOEO on the PCM-controlled side of the relay. If there is none, again repair the open or short in the circuit and retest.
To check the AIR pump solenoid PCM wiring, grounding the control circuit, which is normally operated by the PCM, will tell you if the wiring is intact. Grounding the circuit at the PCM connector with KOEO should activate the AIR pump relay, which in turn should activate the AIR pump and solenoid. If this does not work, there is an open or short in the PCM control circuit. If grounding the control circuit makes the AIR pump and solenoid operate, check that the PCM has good ground paths and no connector damage or water intrusion. If this checks out, suspect an open driver in the PCM.