DTC P0412: Air Relay Control Circuit: Description

The secondary Air Injection (AIR) solenoid is used as a switch to 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 engine vacuum to open the shut-off valve. The PCM driver monitors the control circuit 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.