DTC P0412: Air Relay Control Circuit: Description

The Powertrain Control Module (PCM) controls the solenoid by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply ground for the component that is being controlled. Each driver has a fault line which the PCM monitors. When the PCM commands a component ON, the voltage of the control circuit should be low, near 0 volts. When the PCM commands the control circuit to a component OFF, the voltage potential of the circuit should be high, near the battery voltage. If the fault detection circuit senses a voltage other than what is expected, the fault line status changes, and causes the DTC to set.