Circuit Description

The PCM controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of driver is to supply ground for the controlled component. Each driver has a fault line which PCM monitors. When PCM commands a component on, voltage of control circuit should be low, near zero volts. When PCM commands control circuit to a component off, the voltage potential of the circuit should be high, about battery voltage. If fault detection circuit senses a voltage other than what the PCM expects, the fault line status changes causing DTC to set.

The relay controls the high current flow to the Secondary Air Injection (AIR) pump and AIR solenoid. This allows PCM driver to only have to control the relatively low current used by the relay.