Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
P0412: Secondary Air Injection Solenoid Relay Control Circuit: Description
The secondary air injection (AIR) vacuum control solenoid is used as a switch to direct and control engine vacuum to the AIR shut-off valve.
Voltage is supplied to the AIR solenoid by the ignition 1 voltage circuit. The Powertrain Control Module (PCM) commands the AIR solenoid ON by supplying a ground on the control circuit by an internal switch called a driver. This action completes the circuit and energizes the AIR solenoid allowing vacuum to open the shut-off valve. The PCM driver monitors the control circuit voltage constantly for proper voltage conditions. When the PCM commands the AIR solenoid ON, the circuit voltage should be low, near 0 volts. When the PCM commands the control circuit OFF, the voltage potential of the circuit should be high, near the battery voltage. If the PCM detects a voltage other than what is expected, DTC P0412 sets.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.